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Polymer (v.46, #25)

Editorial board (pp. co2).
Calendar (pp. i-ii).

Characterization of the thermal properties of PLA fibers by modulated differential scanning calorimetry by S. Solarski; M. Ferreira; E. Devaux (pp. 11187-11192).
Polylactide (PLA) has been melt spun to produce multifilament continuous yarns. The thermal characteristics of PLA filaments have been investigated using modulated differential scanning calorimetry (MDSC). With MDSC, it is possible to separate the different thermal events and to analyze them more precisely. The influence of hot drawing on thermal properties of PLA filaments has been studied. Hot drawing promotes an increase of glass transition temperature ( Tg) and a decrease of heat capacity. The cold crystallization spreads on a larger range of temperature and the peak occurs at a lower temperature. The initial degrees of cristallinity of PLA filaments have been calculated thanks to the reversing and non reversing curves of MDSC. Tensile properties of PLA filaments are also investigated.

Keywords: Modulated differential scanning calorimetry (MDSC); Fibers; PLA

Gel-spinning and drawing of gelatin by Ryohei Fukae; Asuka Maekawa; Osamu Sangen (pp. 11193-11194).
Gelatin fibers can be prepared by the gel-spinning method using dimethyl sulfoxide as a solvent. The use of the method and the drawing in a gel state were effective in inducing segmental orientation in gelatin fiber. The fibers showed high values for the mechanical properties of tensile strength of 180MPa and Young's modulus of 3.4GPa.

Keywords: Gelatin; Fiber; Gel-spinning

Cross-sectional analysis of hollow latex particles by focused ion beam–scanning electron microscopy by Elvin Beach; Melinda Keefe; William Heeschen; Deborah Rothe (pp. 11195-11197).

Green–blue luminescence dichroism of cyano-containing poly[( m-phenylene ethynylene)- alt-( p-phenylene ethynylene)] aggregates dispersed in oriented polyethylene by Andrea Pucci; Tarita Biver; Giacomo Ruggeri; L. Itzel Meza; Yi Pang (pp. 11198-11205).
A new highly luminescent cyano-containing poly[( m-phenylene ethynylene)- alt-( p-phenylene ethynylene)] derivative (CN-PPE) has been prepared and blended in micro/nano-sized dispersions into linear low density polyethylene (LLDPE) films by melt-processing. CN-PPE macromolecules show pronounced tendency to form molecular aggregates in the excited state when dispersed in the polymer matrix with emission characteristics depending on the structural order of the luminescent chromophores. In CN-PPE/LLDPE films, the polymer matrix orientation induces effective anisotropic arrangements of the π–π staking interactions between luminescent guest aggregates, thereby generating a pronounced green–blue dichroic emission. The capability to easily modulate the luminescent properties of polyethylene films (from green to blue reversibly) simply by varying CN-PPE concentration or by stretching the polymer matrix, suggests various technological applications in the field of smart and intelligent films from thermoplastic materials.

Keywords: Luminescent polymeric chromophores; Polyethylene orientation; Smart dichroic materials

Crosslinking of cellulose derivatives and hyaluronic acid with water-soluble carbodiimide by A. Sannino; S. Pappad; M. Madaghiele; A. Maffezzoli; L. Ambrosio; L. Nicolais (pp. 11206-11212).
Hydrogels with good mechanical stability are generally obtained by chemical crosslinking. However, the compounds used as crosslinking agents are often highly toxic, and thus they are not recommended as starting materials in view of an environmentally safe production process and a biocompatible product.In this work chemically crosslinked superabsorbent hydrogels have been synthesized from water solutions of hydroxyethylcellulose (HEC), carboxymethylcellulose sodium salt (CMCNa) and hyaluronic acid (HA), using a non-toxic water-soluble carbodiimide (WSC) as crosslinking agent. Sorption capacity both in water and in water solutions at different ionic strength has been investigated, taking into account the effect of different chemical compositions. Moreover, uniaxial compression tests and dynamic-mechanical measurements on water swollen samples have been performed to probe the elastically effective degree of crosslinking of the polymeric network.In vivo tests on humans for the application of this material as a bulking agent in dietary regimes are in process and preliminary results are encouraging.

Keywords: Hydrogel; Crosslinking; Carbodiimmide

Cationic polymerization of 2,4,6,8-tetramethylcyclotetrasiloxane processed by tuning the pH of the miniemulsion by Guillaume Palaprat; Franois Ganachaud; Monique Mauzac; Patrick Hmery (pp. 11213-11218).
The preparation of 2,4,6,8-tetramethylcyclotetrasiloxane (D4H) miniemulsions stabilized by commercial surfactants, i.e. sodium dodecylbenzenesulfonate (NaDBSA) and sodium laurate/lauric acid mixture, was studied and is first reported. Then, the pH was tuned in order to process polymerization through interfacial protonic initiation. With lauric acid, no polymerization was observed, even at high temperature or large acid contents. Such effect is ascribed to the poor dissociation and reactivity of high pKa's carboxylic acids. With NaDBSA, acidification by HCl was enough to initiate the polymerization, but the pH of the continuous phase was shown to have a strong effect on the polymerization process. Optimal conditions (at pH 5) gave chains with average number molar masses around 16,000gmol−1 and polydispersity index close to 1.6, for a total conversion in polymer of about 60% after 2h reaction. Lower pH (4.2) quickly led to a cross-linked network whereas at higher pH (6.1), conversions were too slow (around 10% after 350min).

Keywords: Cationic polymerization; Emulsion; Poly(methylhydrogenosiloxane)

Telechelic polyesters of ethane diol and adipic or sebacic acid by means of bismuth carboxylates as non-toxic catalysts by Hans R. Kricheldorf; Gesa Behnken; Gert Schwarz (pp. 11219-11224).
Dimethyladipate or dimethylsebacate were polycondensed with an excess of 1,2-ethane diol in bulk using two different temperature/time programs. Bismuth(III) n-hexanoate (BiHex3), tin(II)2-ethylhexanoate (SnOct2) and titanium tetrabutoxide were used as catalysts. Only the bismuth catalyst yielded clean telechelic polyesters having two ethylene glycol endgroups. With SnOct2 cyclic oligoesters were obtained as byproducts. Ti(OBu)4 yielded OH-terminated linear chains containing large amounts of diethylene glycol units (detectable up to three ether groups per chain). Furthermore, small amounts of cycles were also formed. Acid-catalyzed polycondensations of ethylene glycol with sebacic acid gave low yields of low oligomers, part of which contained diethylene glycol units.

Keywords: Biodegradable polyesters; Telechelics; Bismuth hexanoate

High performance poly(urethane-imide) prepared by introducing imide blocks into the polyurethane backbone by Tsutomu Takeichi; Koichi Ujiie; Kazuto Inoue (pp. 11225-11231).
A series of novel linear poly(urethane-imide)s were synthesized by the reaction between isocyanate-terminated polyurethane (PU) prepolymer and amine- or anhydride-terminated oligoimide. PU prepolymer was synthesized by reacting polyethylene adipatediol of molecular weight 1000 with tolylene-2,4-diisocyanate at the molar ratio of 2:3 or 1:2. Oligoimide was synthesized from the reaction of 4,4′-(hexafluoroisopropylidene)diphthalic acid with 4,4′-oxydianiline at various molar ratios. Equimolar amounts of PU prepolymer and oligoimide were reacted in N-methyl-2-pyrrolidone, followed by casting on glass plates and heat treatment at 100 and 150°C for 1h each to give linear poly(urethane-imide)s as transparent yellowish brown films. Poly(urethane-imide) films with less of 30% of imide component became elastomer, and films with more than 36% imide component became plastic. The effects of end-groups of oligoimide, molecular weight of oligoimide, and molecular weight of PU prepolymer on the solvent resistance, the tensile properties, viscoelastic properties, and thermogravimetric properties of poly(urethane-imide) films were systematically examined. Solvent resistance and tensile modulus of poly(urethane-imide) films from amine-terminated oligoimides were better than those from anhydride-terminated oligoimides. On the other hand, thermal stability and elongation at break for the poly(urethane-imide) films from anhydride-terminated oligoimides were higher than those from amine-terminated oligoimides.

Keywords: Poly(urethane-imide)s; PU prepolymer; Oligoimide

Organization in sol–gel polymerization of methacrylate co-oligomers containing trimethoxysilylpropyl methacrylate by Josef Vraštil; Libor Matějka; Vladimír Špa?ek; Miroslav Ve?eřa; Luboš Prokůpek (pp. 11232-11240).
The sol–gel polymerization and resulting structures of organic-inorganic systems based on hybrid methacrylate oligomers have been studied using SEC, DSC, and SAXS. The block and random oligomers with narrow polydipersity were prepared by group transfer polymerization. All the oligomers contain 3-(trimethoxysilyl)propyl methacrylates in the chain and form silsesquioxane (SSQO) clusters by hydrolytic polycondensation, serving as cross-linking domains of the organic-inorganic network. The water miscibility and gelation of synthesized oligomers were evaluated. The systems studied can be divided into two groups—gelling and non-gelling oligomers as a result of the competition between cyclization and intermolecular reaction. The extent of cyclization and intermolecular polycondensation depends on the oligomer structure, i.e. position and number of the functional trimethoxysilyl-monomer units, and on molecular weight of the oligomeric chains. Due to the incompatibility of the SSQO framework and organic chains, microphase separation and structure ordering occur during polymerization.

Keywords: Organic–inorganic hybrid; Sol–gel process; Oligomers

Preparation and characterization of hybrid nanocomposite coatings by photopolymerization and sol–gel process by E. Amerio; M. Sangermano; G. Malucelli; A. Priola; B. Voit (pp. 11241-11246).
Organic–inorganic nanocomposite hybrid coatings were prepared through a dual-cure process involving cationic photopolymerization of epoxy groups and subsequent condensation of alkoxysilane groups. The kinetics of the photopolymerization and condensation reactions were investigated; suitable conditions for obtaining a complete conversion of both reactive groups were found. The obtained films are transparent to visible light. The Tg values of the hybrids increase by increasing the TEOS content in the photocurable formulation. Also, a significant increase in surface hardness could be obtained for the hybrid systems. AFM analysis gave evidence of a strong interaction between the organic and inorganic phase with the formation of silica domains in the nanoscale range.

Keywords: Hybrid nanocomposites; Cationic photopolymerization; Sol–gel process

Synthesis and properties evaluation of novel halogenated polyimides designed to prepare functional polymers by Eva M. Maya; Angel E. Lozano; Javier de Abajo; Jose G. de la Campa (pp. 11247-11254).
Three new aromatic polyimides containing one or two replaceable halogen atoms in the repeat unit have been prepared by one-pot polycondensation at high temperature from dianhydrides and diamines containing halogen atoms. The halogenated polyimides exhibited good thermal properties and great solubility in a wide range of organic solvents, which make them good candidates to prepare functional polymers. They also showed film-forming capabilities, good mechanical properties, and a very low ability to take water, with values of only around 1% water uptake. To show the usefulness of these polyimides as functional polymers, the halogen group of two of them was successfully replaced by 4- tert-butyl phenyl or 4- tert-butyl phenyl ethynyl groups by a Suzuki or a Sonogashira reaction, respectively.

Keywords: Polyimides; Halogen; Modification

The influence of clay and elastomer concentration on the morphology and fracture energy of preformed acrylic rubber dispersed clay filled epoxy nanocomposites by S. Balakrishnan; P.R. Start; D. Raghavan; S.D. Hudson (pp. 11255-11262).
The influence of toughener and clay concentration on the morphology and mechanical properties of three-phase, rubber-modified epoxy nanocomposites was studied. Nanocomposite samples were prepared by adding octadecyl ammonium ion exchanged clay to a dispersion of pre-formed acrylic rubber particles in liquid epoxy, so as to minimize alteration to the rubber morphology in the final cured specimen. The state of clay platelet exfoliation and rubber dispersion in the cured nanocomposites was studied using transmission electron microscopy. The amounts of clay platelet separation and dispersion of clay aggregates in the epoxy matrix were found to be sensitive to clay and toughener concentration, and clay platelets preferentially adsorb to the rubber particles. Tensile modulus and strength increase and ductility decreases with increasing organoclay content, while rubber has the opposite effects on the properties of epoxy resin. When both additives are present in epoxy resin, a favorable combination is produced: ductility is enhanced without compromising modulus and strength. Modulus and strength are improved by nano and micro dispersion of nanoclay in the epoxy matrix, whereas elongation and toughness are improved by clay adsorption to the rubber particle surface, which promotes cavitation. The glass transition temperature of epoxy resin remains relatively unchanged with clay addition.

Keywords: Preformed acrylic rubber; Epoxy; Nanocomposite

Synthesis of new versatile functionalized polyesters for biomedical applications by Vronique Nadeau; Grgoire Leclair; Shilpa Sant; Jean-Michel Rabanel; Richard Quesnel; Patrice Hildgen (pp. 11263-11272).
A new family of branched polymers was synthesized for different biomedical applications such as the preparation of targeted nanoparticulate drug carriers. They are new copolymers of hydroxy-acids and allyl glycidyl ether. The functional groups (allyl-, hydroxyl- and carboxyl-) to which various groups will be grafted are linked to the polymer backbone. The resulting polymers were characterized by1H NMR,13C NMR, size exclusion chromatography (SEC), elemental analysis and differential scanning calorimetry (DSC). In vitro cytotoxicity assays were also conducted to ensure biocompatibility of the polymers. In order to obtain some structural evidences, different molecules have been grafted on the pendant groups. The method allows a rapid and easy synthesis of allyl-, hydroxyl- and carboxyl-branched degradable polymers for grafting various bioactive molecules.

Keywords: Branched polymer; Biocompatible; Bioadhesive

Photopolymerization of butyl acrylate-in-water microemulsions: Polymer molecular weight and end-groups by Kaveri Jain; John Klier; Alec B. Scranton (pp. 11273-11278).
Solubilization of butyl acrylate in water using sodium dodecyl sulfate (SDS) and 1-pentanol produced transparent oil-in-water microemulsions stable at room temperature. These microemulsions were polymerized using a two-component water-soluble initiator system comprising of Rose Bengal (RB) and methyldiethanolamine (MDEA). These compounds undergo photo-induced electron transfer upon absorption of visible light to produce amine radicals active in free radical polymerization. Analysis of the NMR spectra of polymers revealed only monomer peaks and amine fragments which were incorporated as the polymer ends. Effect of initiator composition on polymer length was also investigated using GPC. When RB concentration was increased with constant concentration of excess MDEA, the average chain length decreased up to a specific concentration where after the polymer length reached an asymptotic value. Experiments were performed to identify this asymptotic value and it was observed that as the MDEA concentration was increased, the asymptotic values of number average degree of polymerization decreased.

Keywords: Microemulsion; Photopolymerization; Acrylates

A comparative structure–property study of methylphenylated and fluoromethylphenylated poly(aryl ethers) and their gas permeabilities and permselectivities by Baijun Liu; Ying Dai; Gilles P. Robertson; Michael D. Guiver; Wei Hu; Zhenhua Jiang (pp. 11279-11287).
Two novel poly(aryl ether)s, dimethylphenylated poly(ether nitrile) (6H-PEN) and dimethylphenylated poly(ether ether ketone) (6H-PEEK), derived from (3,5-dimethylphenyl)hydroquinone monomer, were synthesized via aromatic nucleophilic substitution polycondensation. They showed high glass transition temperatures and were soluble in common solvents. A comparison of gas permeabilities and permselectivities among methylphenylated (3H-PEEK and 3H-PEN), trifluoromethylphenylated (3F-PEEK and 3F-PEN), dimethylphenylated (6H-PEEK and 6H-PEN) and 3,5-ditrifluoromethylphenylated (6F-PEEK and 6F-PEN) poly(aryl ether)s were studied. Compared with the methylated polymers, the corresponding fluoromethylated polymers had generally higher permeabilities. The 3F and 6F polymers had combined permeabilities and permselectivity properties attractive for O2/N2 separation. 6F-PEN exhibited the best gas separation properties for the O2/N2 pair, and P(O2), and P(O2)/ P(N2) values were 6.6 and 5.9, respectively.

Keywords: Gas permeability; Poly(ether ketone)s; Fluoropolymers

Preparation and characterization of manganese, nickel and cobalt ferrites submicron particles in sulfonated crosslinked networks by L.C. Santa Maria; M.A.S. Costa; J.G.M. Soares; S.H. Wang; M.R. Silva (pp. 11288-11293).
Magnetic submicron particles of MnFe2O4, NiFe2O4 or CoFe2O4 were created in or around the porous sulfonated beads based on poly(styrene- co-divinylbenzene) using an in situ inorganic precipitation procedure. The copolymer beads were treated with a mixed iron/cobalt chloride electrolyte and the doped copolymer networks were converted to their oxides by reaction with sodium hydroxide and potassium nitrate in aqueous solution. Energy dispersive X-ray spectroscopy (EDS) coupled to scanning electron microscopy (SEM) allowed the observation of the presence of submicron particles in the 0.1–0.5μm size range, which chemical microanalysis of emitted X-rays revealed the presence of metal oxide particle, such as nickel, manganese or cobalt iron oxide. The morphological features of the binary material particles have depended on the ferrite type. All beads have presented dispersed and agglomerated submicron particles of ferrite located on their surface and inner part as well. Magnetization data of the microbeads showed good ferromagnetic behavior.

Keywords: Polymer; Magnetic properties; Ferrite

Preparation of stable polyurethane–polystyrene copolymer emulsions via RAFT polymerization process by Yu-Zi Jin; Yoon Bong Hahn; Kee Suk Nahm; Youn-Sik Lee (pp. 11294-11300).
Stable polyurethane–polystyrene (PU–PS) copolymer emulsions were prepared by the polymerization of 2-hydroxyethyl acrylate (HEA)-capped PU macromonomer and styrene, using azobis(isobutyronitrile) (AIBN), a radical initiator, and 4-((benzodithioyl)methyl)benzoic acid, a reversible addition–fragmentation chain transfer (RAFT) agent. As the molar ratio of the RAFT agent to AIBN increased, the zeta potential of the resulting copolymer emulsion increased, but the average size and size distribution of the emulsion droplets decreased. A living polymerization of HEA end-capped PU macromonomer and styrene was characterized by a linear increase in the molecular weight and decrease in the molecular weight distribution with consumption of monomers. The tensile strength, hardness and water-resistance of the copolymer films, prepared from the PU–PS copolymer emulsions, were much greater than those of the films prepared from the pure PU emulsion. The copolymer emulsions, prepared via the RAFT polymerization process, are expected to exhibit better storage stability than those prepared via the conventional free radical polymerization process, due to the presence of carboxyl groups derived from the RAFT agent at the PS block termini.

Keywords: Living polymerization; PU macromonomer; RAFT process

Effects of tris(pentafluorophenyl)borane on the activation of zerovalent-nickel complex in the addition polymerization of norbornene by Youngchan Jang; Hyun-Kyung Sung; Seunghwa Lee; Cheolbeom Bae (pp. 11301-11310).
The effects of B(C6F5)3 on the activation of the Ni(0) and Ni(II) complexes were studied in the polymerization of norbornene. The Ni(0) complex, such as bis(1,5-cyclooctadiene)nickel (Ni(COD)2 (1), biacetylbis(2,6-diisopropylphenylimmine)(1,3-butadiene)nickel (2), or tetrakis(triphenylphosphine)nickel (5), in combination with B(C6F5)3, was determined to have high activity in the polymerization of norbornene. On the other hand, the Ni(II) complex with B(C6F5)3 did not provide any activity at all under analogous conditions regardless of the structure of the Ni(II) complex. The use of other borane compounds, such as B(C6H5)3, BEt3, and BF3 etherate, with Ni(COD)2 (1) in place of B(C6F5)3 clearly showed the main functions of B(C6F5)3. The high Lewis acidity of B(C6F5)3 enabled it to activate catalytic complexes, thus inducing polymerization. The study of the1H,13C, and19F NMR spectra of the polynorbornene produced with Ni(COD)2 (1) and B(C6F5)3, in the presence or absence of ethylene, showed that the initiation of addition polymerization occurred through the insertion of the exo face of the norbornene into the Ni–C bond of the C6F5 ligand. A new polymerization mechanism was proposed in norbornene polymerization, wherein the active complex formed from Ni(COD)2 (1) and B(C6F5)3 acts as a catalyst.

Keywords: Norbornene polymerization; Zerovalent-nickel complex; Tris(pentafluorophenyl)borane

Surface energy inducing asymmetric phase distribution in films of a bynary polymeric blend by Monica Bertoldo; Maria Beatrice Coltelli; Lidia Miraglia; Piero Narducci; Simona Bronco (pp. 11311-11321).
The phase morphology of blends of low density polyethylene (PE) with low molecular weight copolyamide (CPA) was investigated in films having 50–100μm thickness. Films were prepared by compression moulding between two surfaces with different polarity, namely teflon and aluminium sheets, in a parallel plate heating press. The film surface characterization and surface energy deduction were performed by FT-IR/ATR spectroscopy and contact angle measurements, respectively. Moreover, the morphology and phase distribution were investigated by scanning electron microscopy both on the surfaces and on the cryogenic section of the films.The copolyamide resulted to be the dispersed phase in all compositions (90/10, 95/5, 97.5/2.5 and 99/1 PE/CPA) and the shape, dimension and distribution of the domains depending on temperature, pressure, time and nature of the surfaces used during the compression stage.The experimental evidences were discussed with respect to the different surface energies of the type of moulding material during the film preparation and related compatibility of the components.

Keywords: Polyethylene blends; Surface energy; Polyethylene/copolyamide films

Synthesis, characterization and thermodynamic properties of poly(3-mesityl-2-hydroxypropyl methacrylate- co- N-vinyl-2-pyrrolidone) by Aslışah Açıkses; İsmet Kaya; Ülkü Sezek; Cumhur Kırılmış (pp. 11322-11329).
Poly(3-mesityl-2-hydroxypropyl methacrylate- co- N-vinyl-2-pyrrolidone) P(MHPMA- co-VP) was synthesized in 1, 4-dioxane solution using benzoyl peroxide (BPO) as initiator at 60°C. The copolymer was characterized by1H13C NMR, FT-IR, DSC, TGA, size exclusion chromatography analysis (SEC) and elemental analysis techniques. According to SEC, the number-average molecular weight ( Mn), weight-average molecular weight ( Mw) and polydispersity index (PDI) values of PMHPMA- co-VP were found to be 58,000, 481,000g/mol and 8.26, respectively. According to TGA, carbonaceous residue value of PMHPMA- co-VP was found to be 6% at 500°C. Also, some thermodynamic properties of PMHPMA- co-VP such as the adsorption enthalpy, Δ Ha, molar evaporation enthalpy, Δ Hv, the sorption enthalpy,ΔH1s, sorption free energy,ΔG1s, sorption entropy,ΔS1s, the partial molar free energy,ΔG1∞, the partial molar heat of mixing,ΔH1∞, at infinite dilution was determined for the interactions of PMHPMA- co-VP with selected alcohols and alkanes by inverse gas chromatography (IGC) method in the temperature range of 323–463K. According to the specific retention volumes,Vg0, the weight fraction activity coefficients of solute probes at infinite dilution,Ω1∞, and Flory–Huggins interaction parameters,χ12∞ between PMHPMA- co-VP-solvents were determined in 413–453K. According toΩ1∞ andχ12∞, selected alcohols and alkanes were found to be non-solvent for PMHPMA- co-VP at 413–453K. The glass transition temperature, Tg, of the PMHPMA- co-VP found to be 370 and 363K, respectively, by IGC and DSC techniques, respectively.

Keywords: Poly(3-mesityl-2-hydroxypropyl methacrylate-; co; -; N; -vinyl-2-pyrrolidone); Synthesis and characterization; Inverse gas chromatography

A depth-resolved look at the network development in alkyd coatings by confocal Raman microspectroscopy by Beta Marton; Leo G.J. van der Ven; Cees Otto; Natallia Uzunbajakava; Mark A. Hempenius; G. Julius Vancso (pp. 11330-11339).
The formation of molecular networks related to the consumption of unsaturated carbon–carbon double bonds (CC) during oxidative drying of alkyd coating films incorporating unsaturated fatty acids was studied. The concentration of CC bonds was measured as a function of drying time and distance from the exposed film surface (depth) using confocal Raman microspectroscopy (CRM). The change in spatial distribution of the CC double bond concentration across the film cross section provides information on the kinetics of the oxidative cross-linking process in the alkyd films. It was found that the CC bond consumption is not homogeneous across the depth of the drying film. The results obtained allowed us to quantitatively monitor the progress of the drying process and the movement of the ‘drying front’ within the coating films. The drying profiles suggest that oxygen penetration into the coating film is a rate-limiting factor in the drying process. Depth profiles during the film forming process develop due to local variations in the oxygen solubility, diffusion coefficient of oxygen, and available amount of double bonds for cross-linking. The influence of several industrially relevant factors, like oil length of the alkyd resin, thickener, solvent, and drier on the film formation process is discussed. Depth resolution of the analytical approach and spatial accuracy of confocal Raman microspectroscopy are also treated.

Keywords: Alkyd paint; Cross-linking; Confocal Raman microspectroscopy, Depth profile of curing

Chain conformational transformations in syndiotactic polypropylene/layered silicate nanocomposites during mechanical elongation and thermal treatment by Vasilis G. Gregoriou; Georgia Kandilioti; Stavros T. Bollas (pp. 11340-11350).
Polymer nanocomposites prepared by melt-mixing syndiotactic polypropylene (sPP) with a quaternary modified montmorillonite have been studied with FT-IR and XRD spectroscopic techniques. FT-IR spectroscopic analysis has shown that the addition of the nanoclay results in a higher helical content for the syndiotactic polypropylene matrix. Furthermore, FT-IR spectroscopy showed that the presence of the nanoclay hinders the polymeric chains from achieving the degree of transformation from helical to trans-planar form during the application of mechanical stress compared to the neat sPP case. Accordingly, the sPP nanocomposites show a higher tendency relative to neat sPP to return to the initial helical conformation upon either releasing the applied mechanical tension or upon exposing to heat at 120C. Additionally, XRD patterns provided evidence that the use of low concentration of nanoclay (1%) resulted in partially exfoliated nanocomposites, while only intercalated nanostructures were produced at high nanoclay contents (10%). However, the application of stress can improve the degree of exfoliation of an sPP nanocomposite. In addition, linear dichroic infrared measurements which allow the monitoring of the influence of the nanoclay on the orientation of the polymeric chains during the application of stress showed that the trans-planar infrared bands exhibit lower orientation in comparison to the same bands in neat sPP, while the addition of nanoclay has no particular influence on the orientation of the infrared bands that are related to helical conformations. Finally, dynamic mechanical analysis (DMA) verified the enhanced mechanical properties of the sPP nanocomposites relative to neat sPP, whereas differential scanning calorimetry (DSC) depicted a slight increase in the glass transition temperature of the polymeric matrix in these nanocomposites, especially for low clay concentrations.

Keywords: Nanocomposites; FT-IR; Conformational transformations

Comparative study of localized side group in poly(2,3 and 4 methyl cyclohexyl methacrylate)s. TSDC measurements by Gustavo Domnguez-Espinosa; Maria J. Sanchis; Ricardo Daz-Calleja; Claudia Pagueguy; Ligia Gargallo; Deodato Radic (pp. 11351-11358).
By means of thermal sampling techniques, the fine structure of the γ-relaxation zone of poly(methyl cyclohexyl methacrylate)s (P2MCHMA), (P3MCHMA), (P4MCHMA) were analyzed. Results reveal that in this relaxation zone, at least two peaks are present. These peaks are attributed to the cis and trans isomers. Loss permittivity of the polymers under study in this relaxation zone has been reproduced from the partial depolarization data by using the elementary relaxation times and activation energies. Results are in relatively good agreement with the experimental data previously obtained. Molecular mechanic calculations have been carried out in order to elucidate the characteristics and molecular origin of the relaxations observed in this zone. An interpretation of the height of the peaks associated to the cis- and trans-isomer in terms of strain energy (SE) have been carried out.

Keywords: Poly(methyl cyclohexyl methacrylate)s; Thermally stimulated depolarization currents; Molecular mechanics calculations

Crystallization behavior of polymer/montmorillonite nanocomposites. Part I. Intercalated poly(ethylene oxide)/montmorillonite nanocomposites by Douwe Homminga; Bart Goderis; Igor Dolbnya; Harry Reynaers; Gabriel Groeninckx (pp. 11359-11365).
The influence of montmorillonite (MMT) silicate layers on the semicrystalline morphology development of the poly(ethylene oxide) (PEO) matrix of PEO/MMT nanocomposites has been investigated by using X-ray diffraction, differential scanning calorimetry, light microscopy and time-resolved simultaneous small- and wide-angle X-ray scattering. The silicate layers act as nucleating agents for the crystallization of PEO, but at high contents also have a retarding effect on the crystal growth. In that case they are non-crystallisable barriers in the crystallization of the PEO matrix. The lamellar semicrystalline structures of pure PEO and the PEO/MMT nanocomposites are, however, identical.

Keywords: Poly(ethylene oxide); Nucleating agent; Nanocomposite

Rheological evaluation of the influence of polymer concentration and molar mass distribution on the formation and performance of asymmetric gas separation membranes prepared by dry phase inversion by Johannes C. Jansen; Marialuigia Macchione; Cesare Oliviero; Raniero Mendichi; Giuseppe A. Ranieri; Enrico Drioli (pp. 11366-11379).
Asymmetric gas separation membranes were prepared by the dry-casting technique from PEEKWC, a modified amorphous glassy poly(ether ether ketone). The phase inversion process and membrane performance were correlated to the properties of the polymer and the casting solution (molar mass, polymer concentration, solution rheology and thermodynamics). It was found that a broad molar mass distribution of the polymer in the casting solution is most favourable for the formation of a highly selective membrane with a dense skin and a porous sub-layer. Thus, membranes with an effective skin thickness of less than 1μm were obtained, exhibiting a maximum O2/N2 selectivity of 7.2 and a CO2/CH4 selectivity of 39, both significantly higher than in a corresponding thick dense PEEKWC membrane and also comparable to or higher than that of the most commonly used polymers for gas separation membranes. The CO2 and O2 permeance were up to 9.5×10−3 and 1.8×10−3m3/(m2hbar) (3.5 and 0.67 GPU), respectively.

Keywords: Gas separation membrane; Dry phase inversion; Rheology

Linear and hyperbranched liquid crystalline polysiloxanes by Tomasz Ganicz; Tadeusz Pakula; Witold Fortuniak; Ewa Białecka-Florjańczyk (pp. 11380-11388).
A series of liquid crystalline (LC) polymers having biphenyl (–C6H4C6H4R; R=H, OC11H23, OC(O)CH(Cl)CH2CH2COOCH2CH3) 4-methoxyphenyl benzoate (–C6H4C(O)OC6H4OCH3) and cholesteryl type mesogenic moieties were synthesized. They were made from respective –Si(CH3)2H terminated mesogens and vinyl functionalized linear and star shape branched polysiloxanes of comb-like and dendritic topologies and were analyzed using WAXS and SAXS techniques. Contrary to the well defined typical dendrimers, in which mesogenic groups are present in an outer sphere, the dendritic systems described here contain such groups also inside the dendritic core. It was found that star shape and dendritic LC structures exhibited various calamitic mesophases (SmA, N* and SmC*) depending on the type of mesogenic groups. On the contrary, the comb-like structures give rise to formation of hexagonal phase, even though they contain typical rod-like mesogenic moieties. For the series of 4-methoxyphenyl benzoate substituted polymers the thorough studies of the relationship between their liquid crystalline properties and topology of siloxane skeleton was determined. Mechanical properties of the LC materials were also studied.

Keywords: Liquid crystal; Hyperbranched polymer; Polysiloxane

Impact of acid containing montmorillonite on the properties of Nafion membranes by Jean-Michel Thomassin; Christophe Pagnoulle; Giuseppe Caldarella; Albert Germain; Robert Jrme (pp. 11389-11395).
The counter-ions of montmorillonite have been exchanged for ammonium cations containing either a sulfonic acid or a carboxylic acid in order to improve the performances of sulfonated membranes in direct methanol fuel cell. These layered silicates have been dispersed within Nafion by solution mixing. Comparison with conventional organo-modified montmorillonite (Cloisite 30B) shows that the incorporation of carboxylic acid in the clay galleries improves the filler dispersion and, consequently, the methanol barrier properties. Moreover, the negative impact of Cloisite 30B on the ionic conductivity is restricted.

Keywords: Fuel cell; Nafion; Montmorillonite

Morphology of PEO/PDMS blends during shear: Coexistence of two droplet/matrix structures and additive effects by Verena E. Ziegler; Bernhard A. Wolf (pp. 11396-11406).
The morphologies of blends of polyethyleneoxide (PEO 37) and poly(dimethylsiloxane)s (PDSM), with viscosity ratios, λ, of approximately one (PDMS 230) or 2.8 (PDMS 314, being the component of higher viscosity) and interfacial tensions on the order of 10mN/m, were investigated at 70°C as a function of shear rate (up to 10s−1) and of time. For the system PEO 37/PDMS 230 we have also studied the influence of the compatibilizer dimethyl–ethyleneoxide–copolymer (PDMS- co-PEO), which is only reasonably soluble in PEO. To investigate the morphologies we have used an optical shear cell in combination with a light microscope. The most important observation consists in the formation of two coexisting droplet/matrix structures for volume fractions of PDMS ranging from 0.4 to 0.6 for both λ values; the presence of the copolymer extends this region to 0.7. In the case of λ≈1 the average droplet radii are within experimental error independent of composition and morphology; for λ=2.8 they depend on the matrix phase in which they are contained and do again not vary with composition. The reduction in drop size caused by the copolymer is markedly larger if PEO forms the matrix. The present morphological observations suggest that the two coexisting droplet/matrix phases develop out of a single droplet/matrix structure via coalescence processes.

Keywords: Polymer blends; Morphology under shear; Phase inversion

Suppression of inhomogeneities in hydrogels formed by free-radical crosslinking copolymerization by Nermin Orakdogen; Mine Yener Kizilay; Oguz Okay (pp. 11407-11415).
Network microstructures of poly(acrylamide) (PAAm) and poly( N, N-dimethylacrylamide) (PDMA) hydrogels were compared by static light scattering and elasticity measurements. The hydrogels were prepared by free-radical crosslinking copolymerization of the monomers acrylamide (AAm) or N, N-dimethylacrylamide (DMA) with N, N′-methylenebis(acrylamide) as a crosslinker. During the formation of PAAm gels, the reaction time dependence of the scattered light intensity exhibits a maximum at a critical reaction time, while in case of PDMA gels, both a maximum and a minimum were observed, corresponding to the chain overlap threshold and the gel point, respectively. This difference in the time-course between the two gelling systems is due to the late onset of gelation in the DMA system with respect to the critical overlap concentration. Compared to the AAm system, no significant scattered light intensity rise was observed during the crosslinking polymerization of DMA. It was shown that, regardless of the crosslinker ratio and of the initial monomer concentration, PDMA gel is much more homogeneous than the corresponding PAAm gel due to the shift of the gelation threshold to the semidilute regime of the reaction system. The results suggest that the spatial gel inhomogeneity can be controlled by varying the gel point with respect to the critical overlap concentration during the preparation of gels by free-radical mechanism.

Keywords: Hydrogels; Gelation; Inhomogeneity

Temperature dependent elastic–plastic behaviour of polystyrene studied using AFM force–distance curves by Senthil Kumar Kaliappan; Brunero Cappella (pp. 11416-11423).
Force–displacement curves have been obtained on two polystyrene samples, having different molecular weight, at various temperatures and probe rates using an atomic force microscope. The force–displacement curves have been analysed using a novel method, which extends continuum elastic contact theories also to the plastic deformations. The Young's modulus and the yielding force of the two polystyrene samples have been determined as a function of temperature and frequency. It was also possible to calculate the Williams–Landel–Ferry coefficients for measurements above the glass transition temperature, and the viscoelastic activation energy for measurements below the glass transition temperature using the Arrhenius equation. All the calculated coefficients were in very good agreement with the literature values. The measured quantities span a wide range of temperature (85°C) and frequency (eight decades) and the shifts of all the quantities calculated from force–displacement curves obey the Williams–Landel–Ferry and Arrhenius equation with the same parameters. Quantitative and qualitative comparison of the Young's modulus, of the stiffness in the plastic region and of the yielding force of the two polystyrene samples revealed different viscoelastic behaviour because of the variation in glass transition temperature of the two samples, due to their difference in the molecular weight.

Keywords: Force–displacement curves; Viscoelastic properties; Time–temperature superposition

Microstructural characterisation of surfactant treated nylon fibres by Stephen M. King; David G. Bucknall (pp. 11424-11434).
Small-angle neutron scattering and differential scanning calorimetry have been used to probe for changes in the microstructure of nylon fibres following exposure to surfactant, acid and alkali solutions. SANS was also used to investigate fibres that had been subjected to intentional loading, environmental exposure, and natural ageing. A number of structural parameters have been derived. The data are capable of differentiating between untreated, treated, loaded, and used fibres. Mostly subtle effects are observed. Only exposure to concentrated acid solutions, or applied strain, imparted any significant structural perturbation. These findings, though relevant in a number of areas of application of nylon fibres, are discussed with particular reference to nylon ropes and the laundering of nylon textiles.

Keywords: Nylon; SANS; Fibre structure

Polymorphism and mechanical properties of syndiotactic polystyrene films by Concetta D'Aniello; Paola Rizzo; Gaetano Guerra (pp. 11435-11441).
The dynamic–mechanical behaviour and the tensile moduli of unstretched and stretched semicrystalline s-PS films, presenting different polymorphic forms (α, γ, δ and clathrate) but similar crystallinity and orientation, have been compared. The main aim is to elucidate the possible influence of different crystalline phases, being largely different in chain conformation and density, on mechanical properties of s-PS semicrystalline samples. For unstretched films presenting a preferential perpendicular orientation of the chain axes, the highest elastic modulus is observed for films with the high density γ phase while for uniaxially oriented films the highest modulus is observed for films with the trans-planar α phase. As for the clathrate films, the guest molecules when only included into the crystalline clathrate phase, have no plasticizing effect.

Keywords: Syndiotactic polystyrene; Polymorphism; Mechanical properties

Characterization on mixed-crystal structure and properties of poly(butylene adipate- co-terephthalate) biodegradable fibers by X.Q. Shi; H. Ito; T. Kikutani (pp. 11442-11450).
Biodegradable ideal random copolymer poly(butylene adipate- co-terephthalate) (PBAT), with 44mol% butylene terephthalate (BT), was melt-spun into fibers with take-up velocity up to 5km/min. The structure development and properties of the as-spun fibers were investigated through birefringence, WAXD, SAXS, DSC and tensile test. Despite of the ideal randomness and composition (1:1) of PBAT copolymer, PBAT fiber showed well-developed PBT-like crystal structure, while its melting temperature (ca. 121C) was over 100C lower than that of PBT. Based on the quantitative analyses on the lattice spacing, the crystallinity and the fraction of crystallizable BT sequences, the crystal structure of PBAT was characterized to be formed by mixed-crystallization of BT and BA units, where BA units were incorporated into BT lattice. This mixed-crystal structure was found to undergo PBT-like reversible crystal modification with the application and removal of tensile stress. This crystal modification was found to occur in a higher strain region compared with that of PBT fibers.

Keywords: Poly(butylene adipate-; co; -terephthalate) (PBAT); Mixed-crystallization; Crystallizable sequences

Bulk free radical polymerizations of methyl methacrylateunder non-isothermal conditions and with intermediate additionof initiator: Experiments and modeling by Jitendra S. Sangwai; Shrikant A. Bhat; Sanjay Gupta; Deoki N. Saraf; Santosh K. Gupta (pp. 11451-11462).
Experimental data on the monomer conversion, xm, and the weight average molecular weight, Mw, have been generated under several isothermal and non-isothermal conditions for the polymerization of methyl methacrylate in a rheometer-reactor assembly. The non-isothermal results, in particular, can be used to provide more stringent tests of kinetic models than isothermal data alone. A simple empirical model has been used to describe this system that accounts for the gel (Trommsdorff) and glass effects. The model involves only xm and the temperature, and is quite general. The model parameters are tuned using only three sets of isothermal data. Good agreement is found between the experimental results and model predictions for a whole variety of experimental conditions, including non-isothermal operation and with intermediate addition of initiator. Because of its generality, this model is quite suitable for use for on-line optimizing control as well as for describing industrial reactors.

Keywords: Bulk free radical polymerization; Kinetics; Non-isothermal polymerizations

Miscibility in blends of linear and branched poly(ethylene oxide) with methacrylate derivative random copolymers and estimation of segmental χ parameters by Hiroki Takeshita; Tomoo Shiomi; Takaki Suzuki; Tsukasa Sato; Masamitsu Miya; Katsuhiko Takenaka; Sirirat Wacharawichanant; Siriporn Damrongsakkul; Sarawut Rimdusit; Supakanok Thongyai; Varun Taepaisitphongse (pp. 11463-11469).
Miscibility in the blends of poly(ethylene oxide) (PEO) with n-hexyl methacrylate-methyl methacrylate random copolymers (HMA-MMA) and 2-ethylhexyl methacrylate-MMA random copolymers (EHMA-MMA) was evaluated using glass transition and light scattering methods. EHMA-MMA was more miscible with PEO than HMA-MMA. Both blends of PEO with HMA-MMA and EHMA-MMA showed UCST-type miscibility although homopolymer blends PEO/PMMA were predicted to be of LCST-type. This was attributed to an increase in the exchange enthalpy with increasing HMA or EHMA composition in the random copolymer. From the copolymer composition dependence of miscibility the segmental χ parameters of HMA/MMA, EHMA/MMA, EO/HMA and EO/EHMA were estimated using the Flory–Huggins theory extended to random copolymer systems. Miscibility in the blends of branched PEO with HMA-MMA whose HMA copolymer composition was 0.16 was compared with that in the linear PEO blends. The former blends were more miscible with HMA-MMA than the latter one by about 35°C at the maximum cloud point temperature.

Keywords: Random copolymer blend; Flory–Huggins; χ; parameter; Branched polymer

Diffusion of probe polystyrenes with different molecular weights in poly(methyl methacrylate) gels and inhomogeneity of the network structure as studied by time-dependent diffusion NMR spectroscopy by Kazuhiro Kamiguchi; Shigeki Kuroki; Mitsuru Satoh; Isao Ando (pp. 11470-11475).
Poly(methyl methacrylate) (PMMA) gels have been prepared with radical polymerization by cross-linking methyl methacrylate monomer using ethylene glycol dimethacrylate as cross-linking monomer in toluene containing polystyrenes (PSs) with Mw from 4000 to 400,000. The diffusion coefficients of the PSs in the PMMA gels swollen in deuterated chloroform have been measured by pulsed field-gradient (PFG)1H NMR method with the diffusing time Δ varied. From the experimental results, it is found that the network structure of PMMA gels prepared in the presence of PSs with Mw=4000 and 400,000 are relatively homogeneous and inhomogeneous, respectively, within the Δ range from 40 to 500ms.

Keywords: Polymer gel; Diffusion; Field gradient NMR

Autoacceleration/degradation of electrochemical polymerization of substituted anilines by M.R. Nateghi; M. Zahedi; M.H. Mosslemin; S. Hashemian; S. Behzad; A. Minnai (pp. 11476-11483).
A comparative study was conducted on the kinetic of electropolymerization of ortho, meta and N-alkyl and alkoxy substituted anilines in 1.0M HCl using cyclic voltammetry. The results show that the net rate of polymer formation was strongly dependent upon the steric hindrance, stability of the radical cations, reactivity of the monomers as well as switch potential. Substituents determine the relative importance of the pathways that lead to formation of polymer or soluble products. The results also indicate that the mutual effect of switch potential on the growth of polymer and its degradation is closely related to the electronic effect of substituent groups. A kinetic expression for the autoacceleration process in the electrochemical polymerization of these aniline derivatives is expressed asν=k[p]n[M]n′+k′[M]n′−k″[p]n″ in which k, k′, [ M], [ p], and k″ are the initiation (nucleation process) rate constant, the rate constant when the polymer is deposited on the electrode, monomer concentration, the total amount of polymer, and the rate constant of degradation process, respectively.

Keywords: Polyaniline; Degradation; Kinetics

Shear stress analysis of a semiconducting polymer based electrorheological fluid system by M.S. Cho; H.J. Choi; M.S. Jhon (pp. 11484-11488).
The electrorheological characteristics of a fluid system with semiconducting poly(naphthalene quinone) (PNQR) particles, synthesized from a Friedel–Craft acylation, were investigated via a rotational rheometer equipped with a high voltage generator. The flow curves of these ER fluids under several applied electric field strengths and particle concentrations were constructed and their flow characteristics were examined via three different rheological constitutive equations of Bingham model, De Kee–Turcotte model and our proposed model. Our proposed equation was found to fit the data very accurately.

Keywords: Semiconducting polymer; Electrorheological fluid; Yield stress

Processing and characterization of epoxy nanocomposites reinforced by cup-stacked carbon nanotubes by Young-Kuk Choi; Yasuo Gotoh; Koh-ichi Sugimoto; Sung-Moo Song; Takashi Yanagisawa; Morinobu Endo (pp. 11489-11498).
The effect of the dispersion, ozone treatment and concentration of cup-stacked carbon nanotubes on mechanical, electrical and thermal properties of the epoxy/CSCNT nanocomposites were investigated. Ozone treatment of carbon fibers was found to increase the surface oxygen concentration, thereby causing the contact angle between water, epoxy resin and carbon fiber to be decreased. Thus, the tensile strength, modulus and the coefficient friction of carbon fiber reinforced epoxy resin were improved. Moreover, the dispersion of fibers in polymer was increased and the electrical resistivity was decreased with the addition of filler content. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus of the polymer was increased by the incorporation of CSCNTs. But the glass transition temperature decreased with increasing fiber loading for the ozone treated fiber composites. The ozone treatment did affect the morphology, mechanical and physical properties of the CSCNT.

Keywords: Nanocomposite; Polymer; Cup-stacked carbon nanotubes

Preparation of thermally stable polymer electrolytes from imidazolium-type ionic liquid derivatives by Hiromitsu Nakajima; Hiroyuki Ohno (pp. 11499-11504).
Thermally stable polymer electrolytes based on ionic liquids were prepared and analyzed. Mono-functional ionic liquid monomers, ionic liquid cross-linkers, and ethylimidazolium-type ionic liquid salts were mixed and polymerized. The ionic liquid-type cross-linkers were effective to prepare thermally stable polymer films. In particular, the copolymerization of cross-linker and ethylimidazolium-type ionic liquid monomers were used to make polymer electrolytes with high ionic conductivities. The copolymerization in ethylmethylimidazolium bis(trifluoromethanesulfonyl)imide gave a transparent film showing no thermal degradation up to 400C.

Keywords: Ionic liquid; Polymer electrolyte; Thermal stability

Electrochemical synthesis of melanin free-standing films by Surya Subianto; Geoffrey Will; Paul Meredith (pp. 11505-11509).
Free-standing melanin films were successfully synthesised electrochemically from dopa. The optimum synthetic conditions such as pH, concentration and current were determined, and it was found that free-standing films could only be formed when ITO glass electrodes were used. The films were analysed by solid state NMR and XPS which showed the presence of indolic moieties characteristic of melanin-type macromolecules. The film showed higher conductivity than chemically synthesised melanin previously reported in literature and also exhibited photoconductivity.

Keywords: Melanin; Polyindolequinone; Electrochemical synthesis

Enhancement of the mechanical properties of poly(styrene- co-acrylonitrile) with poly(methyl methacrylate)-grafted multiwalled carbon nanotubes by Mian Wang; K.P. Pramoda; Suat Hong Goh (pp. 11510-11516).
Poly(methyl methacrylate) (PMMA) was grafted onto multiwalled carbon nanotubes (MWNTs). Composites of PMMA-grafted MWNTs and poly(styrene- co-acrylonitrile) (SAN) were prepared by solution casting from tetrahydrofuran. Since PMMA is miscible with SAN, the two polymers mix intimately to facilitate the dispersion of PMMA-grafted MWNTs in the SAN matrix. The intimate mixing is evidenced by the transparency of the composites. The incorporation of PMMA-grafted MWNTs to SAN (effective MWNT content=0.5–2wt%) leads to increases in storage modulus at 40°C, Young's modulus, tensile strength, ultimate strain, and toughness by 90, 51, 99, 184 and 614%, respectively. Such simultaneous increases in stiffness, strength, ductility and toughness of a polymer by rigid fillers are rarely observed.

Keywords: Poly(styrene-; co; -acrylonitrile); Multiwalled carbon nanotubes; Mechanical properties

New local composition model for polymer solutions by Rahmat Sadeghi (pp. 11517-11526).
A new segment-based local composition model is presented for the excess Gibbs energy of polymer solutions. The excess Gibbs energy of a polymer solution is expressed as a sum of contributions of a combinatorial and a residual excess Gibbs energy term. The truncated Freed correction to Flory–Huggins expression as first correction for the configurational entropy of mixing is used as a combinatorial contribution to the excess Gibbs energy. A new expression based on the local composition concept, which is the NRF-Wilson model, is developed to account for the contribution of the residual excess Gibbs energy. The main difference between this model and the segment-based NRTL model available in the literature is in the nature of the short-range energy parameter and their references states. The utility of the model is demonstrated with the successful representation of the vapor–liquid equilibria, density and viscosity of several polymer solutions. The results show that, the model is valid for the whole range of polymer concentration, from dilute solution up to saturation. The results are compared with those obtained from the segment-based NRTL and segment-based Wilson models. The model presented in this work produces better results.

Keywords: Excess Gibbs energy; NRF-Wilson; Vapor–liquid equilibria

Comprehensive analysis of stereoregularity and sequence distribution in 2- N-carbazolylethyl acrylate and methyl methacrylate copolymers by 2D NMR spectroscopy and their thermal studies by A.S. Brar; Meghna Markanday (pp. 11527-11539).
A series of 2- N-carbazolylethyl acrylate (C) and methyl methacrylate (M) copolymers with varying compositions were prepared in toluene at 60°C using AIBN as an initiator. The molar outfeed ratio ( FC) for various compositions was determined from1H NMR spectra. Reactivity ratios calculated using Kelen–Tudos (KT) and non-linear error in variable (RREVM) methods were found to be rC=0.43±0.8 and rM=2.78±0.52. Molecular weight distribution was determined by gel permeation chromatography (GPC). The methine carbon of C unit showed splitting up to the pentad level in13C{1H} NMR spectra and was found to be sensitive to the variation in C/M copolymer compositions. The backbone methylene and carbonyl carbons of both M and C unit along with α-methyl carbon of the M unit showed both compositional and configurational sensitivity. Distortionless enhancement by polarization transfer (DEPT) helped in differentiating the methylene carbon signals from the methine and methyl carbon resonances. 2D heteronuclear single quantum coherence (HSQC) and 2D total correlation spectroscopy (TOCSY) were used in tandem to deduce all spectral assignments. 2D heteronuclear multiple bond coherence (HMBC) played an important role in studying the stereoregularity of the carbonyl carbon. The trend in variation of glass transition temperature ( Tg) of various C/M copolymer compositions was also studied.

Keywords: 2-; N; -carbazolylethyl acrylate; NMR; Microstructure

Photopolymerization of HEMA/DEGDMA hydrogels in solution by Ling Li; L. James Lee (pp. 11540-11547).
Photopolymerization is a widely used technique to synthesize polymers and hydrogels. The commonly used ultraviolet (UV)-curable mono-, di- or multifunctional vinylated monomers are often volatile, causing difficulty in kinetics analysis such as photo-differential scanning calorimetry (PhotoDSC). In this work, the DSC sample pan is chemically and physically modified such that the resin can be placed uniformly in the sample pan with minimum sample weight loss during measurement. This approach substantially improved experimental accuracy, which in turn provides a better understanding of the reaction kinetics of UV-curable polymers. Kinetic experiments were carried out for poly(2-hydroxyethyl methacrylate) (HEMA)-based hydrogels. The effects of light intensity and water concentration on the reaction kinetics and rheological change was investigated. It was found that increasing the light intensity enhances the polymerization, but too high an intensity slows down the reaction at the later stage. The addition of solvent and high light intensity facilitates the cyclization, delaying macrogelation. The viscosity rise of the resin system and the formed polymer size were also measured using a photorheometer and a particle size analyzer, respectively. The measured gel time, gel conversion and polymer size distribution agree with the kinetic analysis.

Keywords: Free radical photopolymerization; Photo-differential scanning calorimetry; Photo-rheometer

Pressure–volume–temperature dependencies of polystyrenes by L.A. Utracki (pp. 11548-11556).
The pressure–volume–temperature ( PVT) dependencies of four molten polystyrenes (PS) were determined at T=450–530K, and P=0.1–190MPa. In addition, five sets of published PVT data for PS were examined. The Simha–Somcynsky (S–S) lattice-hole equation of state (eos) was used to analyze the data. Fitting the data to eos yielded the characteristic reducing parameters, viz. P*, V*, T*, where from the Lennard–Jones measures of energetic ( ε*), and volumetric ( v*) interactions were calculated. It was found that: (1) the values of the interaction parameters for PS resins varied, viz. 27.7≤ ε*≤35.2, and 35.5≤ v*≤50.2; (2) ε* was dependent on v*, and (3) ε* and v* linearly increased with the logarithm of molecular weight. In addition, these volume-averaged interaction parameters depend on the chain configuration, as well as the presence of additives.

Keywords: Polystyrene; PVT behavior; Equation-of-state

Polystyrenes with macro-intercalated organoclay. Part I. Compounding and characterization by Maryam Sepehr; Leszek A. Utracki; Xiaoxia Zheng; Charles A. Wilkie (pp. 11557-11568).
Nanocomposites of polystyrene (PS) were prepared using a melt compounding or co-solvent method. Two commercial PS were used, and two organoclays—one prepared in this laboratory (COPS), and the other commercial Cloisite® 10A (C10A). The COPS is a product of clay intercalation with a copolymer of styrene and vinyl benzyl tri-methyl ammonium chloride. According to the XRD diffraction data, the clay platelets in COPS and its PNC with PS were relatively well dispersed, i.e. with the interlayer spacings of d001=7–8nm. By contrast, d001 in PNC prepared with C10A was only 4nm. However, the number of clay platelets per stack in PS/COPS was found to be significantly larger than that in PS/C10A, viz. m=3–12, compared to m=2–6. The scanning and transmission electron microscopy indicated that in the PS matrix COPS existed in form of large, immiscible domains.

Keywords: Polystyrene; Nanocomposites; Phase separation

Polystyrenes with macro-intercalated organoclay. Part II. Rheology and mechanical performance by Maryam Sepehr; Leszek A. Utracki; Xiaoxia Zheng; Charles A. Wilkie (pp. 11569-11581).
Polymeric nanocomposites (PNC) of polstyrene (PS) with organoclay were studied for their rheological and mechanical behavior. The organoclay (COPS) is a product of clay quaternization with a copolymer of styrene with vinyl benzyl tri-methyl ammonium chloride. PNC preparation and characterization was described in Part I of this paper. The clay platelets in COPS and its PNC's are well dispersed, i.e. with the interlayer spacings of d001=7–8nm. By contrast, d001=3–4nm for PNC with Cloisite® 10A. However, the COPS in PS formed large, deformable domains. At concentration exceeding 5.8-wt% of COPS, the domains started to form a three-dimensional network with enhanced elasticity and progressive viscoelastic non-linearity. At temperatures of 160–180°C the neat COPS did not flow; its behavior resembled that of a crosslinked elastomer. Application of the time–temperature superposition led to master curves of bending moduli vs. 19 decades of reduced frequency. The curves indicated a transition at ca. 180°C, most likely associated with the disintegration of ammonium ion clusters. With the same amount of clay the mechanical properties of PNC with COPS were slightly worse than those with Cloisite® 10A—the immiscibility of COPS, and the presence of extractable (by the matrix) low molecular weight compounds explain the behavior.

Keywords: Polystyrene; Nanocomposites; Phase separation

Syndiotactic polypropylene as potential material for the preparation of porous membranes via thermally induced phase separation (TIPS) process by Wilfredo Yave; Ral Quijada; Mathias Ulbricht; Rosario Benavente (pp. 11582-11590).
This work reports the flat sheet membrane preparation from syndiotactic polypropylene (sPP) by thermally induced phase separation (TIPS) process. sPP obtained by polymerization using metallocene catalysts and isotactic polypropylene (iPP) also obtained via metallocene catalysis with similar molecular weight were used. The phase diagrams of sPP and iPP with diphenylether as diluent were obtained. The properties of three representative membranes from sPP and three from iPP, prepared using different PP concentrations were evaluated with respect to membrane pore structure, gas flow, liquid displacement (bubble point), and water permeability. Two selected membranes, one from sPP and one from iPP were analysed with regard to polypropylene bulk morphology (X-ray diffraction) and mechanical properties (tensile strength). Under the same formation conditions, membranes with less inter-connected pores and less porous surface were obtained from sPP compared with iPP. Overall, lower permeabilities had been found for the sPP membranes, which were attributed to the difference in pore morphology. The differences between sPP and iPP were also discussed in terms of different driving forces for liquid–liquid demixing as deduced from the phase diagrams. The X-ray analysis had shown that the sPP membranes had a higher amorphous phase content than that in iPP, and the mechanical test had revealed a pronounced ductile behaviour for sPP samples. These results helped to explain the lower permeabilities of the sPP membranes, and their pressure-dependency.

Keywords: Syndiotactic polypropylene; Microfiltration membrane; TIPS process

Rheological study of carbon nanofiber induced physical gelation in polyolefin nanocomposite melt by Antonis Kelarakis; Kyunghwan Yoon; Rajesh H. Somani; Xuming Chen; Benjamin S. Hsiao; Benjamin Chu (pp. 11591-11599).
The rheological behavior of nanocomposites based on elastomeric ethylene–propylene (EP) random copolymer (84.3wt% P) and well-dispersed modified carbon nanofibers (MCNFs) with concentrations from 0.5 to 20wt% were studied by oscillatory-shear rheometry at varying temperatures. At relatively low temperatures, the entanglement density of the polymer chains appeared to increase with filler concentration, ensuring strong MCNF–polymer interactions. At elevated temperatures, pronounced deviations from the ideal melt behavior in the low frequency domain (i.e. positive slopes of the tan δ( ω) curves) were observed, indicating the formation of a three-dimensional percolated network. Following the Winter–Chambon criterion, the transition from pseudo-solid-like to liquid-like behavior (i.e. the critical gel point) upon cooling was determined. The physical gelation induced by MCNFs is a thermo-reversible phenomenon and its origin can be traced to the interactions of nanofillers, where the percolation temperature decreases with filler concentration. Abrupt changes in the critical gelation temperature, the stiffness of the gel and the relaxation exponent were observed in nanocomposites with MCNF loading above 10wt%. This behavior indicates a change of the mechanism of physical gelation at high MCNF loadings that can be explained by the concept of bridge formation of polymer segments between two adjacent nanofillers in concentrated nanocomposites.

Keywords: Ethylene–propylene elastomer; Carbon nanofiber; Nanocomposite

Investigation on the polyamide 6/organoclay nanocomposites with or without a maleated polyolefin elastomer as a toughener by Fang-Chyou Chiu; Sun-Mou Lai; Yu-Lun Chen; Tsung-Han Lee (pp. 11600-11609).
Polyamide 6 (PA 6)-based nanocomposites were prepared using a melt-mixing technique in this study. One commercial organoclay (denoted 30B) and one maleated polyolefin elastomer (denoted POEMA) served as the reinforcing filler and toughener, respectively. The X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive spectroscopy (SEM/EDS) and transmission electron microscopy (TEM) results confirmed the nano-scaled dispersion of 30B in the composites. Different mixing sequences presented similar phase morphology for the same formulated nanocomposites. XRD results also revealed that both 30B and POEMA would induce the formation of γ form PA 6 crystal, with 30B exhibiting a higher efficiency. Differential scanning calorimetry (DSC) results indicated that the addition of 30B altered the crystallization kinetics of PA 6, which was mainly attributed to the prevailing formation of γ form crystal. Complex melting behaviors were observed for neat PA 6 and the nanocomposites. These complex behaviors are associated with different polymorphs and the ‘melting-recrystallization-remelting’ phenomenon. Moderate thermal stability enhancement of PA 6 after adding 30B and/or POEMA was confirmed using thermogravimetric analysis (TGA). The storage modulus, Young's modulus and tensile strength of PA 6 were increased after adding 30B. However, these properties declined after further incorporation of POEMA. The different-processed PA 6/30B/POEMA nanocomposites displayed balanced tensile properties and toughness between those of neat PA 6 and PA 6/30B nanocomposite.

Keywords: PA 6; Organoclay; Nanocomposite

Adhesion of CPO onto high modulus TPO: Lap-shear tests in conjunction with microscopy studies of the fracture surface structure by Zhihui Yin; Yuechun Ma; Warner Chen; Neil Coombs; Mitchell A. Winnik; Rose A. Ryntz; Philip V. Yaneff (pp. 11610-11623).
A lap-shear test was employed to investigate the failure mechanism of a chlorinated polyolefin (CPO) coating on a high-modulus thermoplastic olefin (TPO) substrate fabricated as a blend of a highly crystalline Ziegler-Natta isotactic polypropylene (iPP) and a crystalline metallocene poly(ethylene–butene) (9wt% butene, EB9) impact modifier. The CPO was a chlorinated polypropylene containing 20wt% Cl. The results showed that the fracture strength increased with increasing EB9 content in TPO blends. They also showed that the presence of xylene vapor during the bake step improved the adhesion between CPO and iPP itself (by 40%), but had a much smaller effect for the TPOs. Optical and transmission electronic microscopy images revealed a well-defined skin layer approximately 230μm thick at the mold surface of the injection molded substrates. For the 25wt% EB9 blend (TPO25), this skin layer consists of thin fibers of EB trapped in a transcrystalline iPP matrix, with crystalline lamellae propagating from the matrix across the EB9 domains. Laser scanning confocal fluorescence microscopy (LCFM) and scanning electron microscopy images of iPP/CPO/iPP samples indicate that failure occurred close to the interface between the CPO and the iPP substrate, and, during fracture, the CPO layer maintained its original thickness. For the TPO/CPO/TPO sandwich samples, the fracture surfaces themselves were much rougher than that between CPO and iPP. Substantial deformation of the CPO layer was seen in the fractured samples, and failure was due primarily to cohesive fracture of the CPO in the region adjacent to the TPO substrate. From the perspective of newly introduced environmental regulations restricting aromatic hydrocarbons in automotive coatings, the most important result was the strong adhesion between CPO and TPO25, with little difference between the samples exposed to xylene vapor and those not exposed to xylene.

Keywords: TPO/CPO adhesion; Lap-shear test; Laser confocal fluorescence microscopy scanning electron microscopy

Micro- and nano-structure in polypropylene/clay nanocomposites by F. Perrin-Sarazin; M.-T. Ton-That; M.N. Bureau; J. Denault (pp. 11624-11634).
Polypropylene (PP)/clay nanocomposites prepared by melt blending using different clays and coupling agents based on maleic anhydride-grafted PP (MA-PP) were studied. Clay dispersion using field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscopy (TEM), and PP matrix morphology were characterized. Clay dispersion was improved in the presence of MA-PP, as shown by the higher particles surface density (number of particles/mm2) at all micro-, sub-micro- and nano-levels. The PP spherulite diameter was affected by both the presence of MA-PP and clay dispersion. Clay intercalation, characterized by both complementary X-ray diffraction (XRD) and TEM, was greatly influenced by the characteristics of MA-PP. The use of low molecular weight ( Mw) MA-PP led to a good and uniform intercalation but with no further possibility to exfoliation. The use of higher Mw MA-PP led to a heterogeneous intercalation with signs of exfoliation. The crystallization behavior of nanocomposites was studied by differential scanning calorimetry (DSC). When fine clay dispersion was achieved with MA-PP, clay-nucleating effect was limited and lower crystallization temperature and rates were observed. It was also shown by wide angle X-ray diffraction (WAXD) that clay induced some orientation of α-phase PP crystallites.

Keywords: Polymer nanocomposites; Microstructure; Clay dispersion

Solvent annealing thin films of poly(isoprene- b-lactide) by Kevin A. Cavicchi; Keith J. Berthiaume; Thomas P. Russell (pp. 11635-11639).
The use of solvent annealing to control the microdomain orientation and long-range ordering in poly(isoprene- b-d,l-lactide) thin films was investigated using scanning force microscopy and grazing incidence small angle X-ray scattering (GISAXS). Benzene and chloroform were used as annealing solvents. Both were found to improve the long-range order in the films. Additionally, at high concentrations of chloroform in the film, a perpendicular orientation of cylinders was observed where the solvent was able to mediate interfacial interactions sufficiently to prevent a preferential segregation of one of the blocks to the surface. In situ GISAXS measurements made during solvent swelling and evaporation allowed an examination of the film morphology over a wide range of solvent concentrations providing a efficient route to optimize conditions for morphology control by solvent annealing.

Keywords: Copolymer; Solvent; Annealing

Thermal and mechanical properties of polyhedral oligomeric silsesquioxane (POSS)/polycarbonate composites by Yiqiang Zhao; David A. Schiraldi (pp. 11640-11647).
A series of composite materials were produced incorporating polyhedral oligomeric silsesquioxane (POSS) derivatives into polycarbonate (PC), by melt blending. Significant differences in compatibility were observed depending on the nano-scale filler's specific structure: trisilanol POSS molecules generally provided better compatibility with PC than fully-saturated cage structures, and phenyl-substituted POSS grades were shown to be more compatible with PC than fillers with other functional groups. Trisilanolphenyl-POSS/PC composites possess the best overall performance among the POSS materials tested. The high compatibility between the trisilanolphenyl-POSS and polycarbonate matrix results in generation of transparent samples up to 5wt% POSS content. Slightly enhanced mechanical properties including tensile and dynamic mechanical modulus are observed with the increase of trisilanolphenyl-POSS loading at the cost of decreasing ductility of the nanocomposites. Importantly, upon orientation of the PC/POSS nanocomposite, crystallization of POSS within the oriented material results—this observation is consistent with a growing number of observations which suggest that ‘bottom-up’ formation of structures incorporating multiple POSS cages result from orientation of these nanocomposites, and that the hybrid organic–inorganic inclusions may be at the heart of observed nano-scale reinforcement.

Keywords: Nanocomposite; Blend; Polycarbonate

Use of a respirometer to measure oxidation rates of polymeric materials at ambient temperatures by Roger A. Assink; Mathew Celina; Julie M. Skutnik; Douglas J. Harris (pp. 11648-11654).
The use of a respirometer is introduced as a novel technique for measuring the oxidation rates of thermally degrading polymers. A dual channel respirometer with fuel cell detectors demonstrates sufficient sensitivity to measure the oxidation rates of low-density polymeric samples at ambient temperatures in a relatively short period of time. Samples of low-density polyurethane foam were aged for various lengths of time in sealed chambers at temperatures ranging from 23 to 110C. The extent of oxygen depletion was measured by flushing the chamber with air and comparing the oxygen concentration in the chamber flow to that of a reference flow. Oxidation rates of the 0.1g/cm3 polyurethane foam could be measured in less than 600h of aging time at 23C. This corresponds to approximately 2ppm oxidation by weight. Oxidation rates of the foam were used to calculate acceleration factors over a wide temperature range, including ambient conditions. Acceleration factors for the compressive force of the polyurethane foam were determined at elevated temperatures. Assuming that the aging behavior of compressive force of the foam is correlated to its oxidation rate, it is possible to calculate acceleration factors for the compressive force and predict the performance of the foam at ambient temperatures.

Keywords: Oxidation rate; Thermal degradation; Respirometer

Isothermal crystallization kinetics of poly(ethylene terephthalate)–poly(ethylene oxide) segmented copolymer with two crystallizing blocks by W. Li; Xiaohua Kong; Enle Zhou; Dezhu Ma (pp. 11655-11663).
The isothermal crystallization kinetics and morphology of poly(ethylene terephthalate)–poly(ethylene oxide) (PET30–PEO6) segmented copolymer, and poly(ethylene terephthalate) (PET) and poly(ethylene oxide) (PEO) homopolymers have been studied by means of differential scanning calorimetry (DSC) and a transmission electron microscope (TEM). It is found that the nucleation mechanism and growth dimension of PEO in the copolymer are different from that in the homopolymer, which is attributed to the effect of the crystallizability of PET-blocks. Furthermore, the crystallization rate of PEO-blocks in the copolymer is slower than that in the homopolymer because the PET-blocks phase is always partially solidified at the temperatures when PEO-blocks begin to crystallize. In contrast, the isothermal crystallization rate of PET-blocks in the copolymer is faster than that in the homopolymer because the lower glass transition temperature of the PEO-blocks (soft blocks) increases the mobility of the PET-blocks in the copolymer.

Keywords: PET–PEO segmented copolymer; PET; PEO

Analysis of ductile and brittle failures from creep rupture testing of high-density polyethylene (HDPE) pipes by Rajendra K. Krishnaswamy (pp. 11664-11672).
A comprehensive analysis of ductile and brittle failures from creep rupture testing of a wide spectrum of HDPE pipes was conducted. The analysis indicates that the ductile failure of such pipes is primarily driven by the yield stress of the polymer (or pipe). Examination of ductile failure data at multiple temperatures indicates a systematic improvement in performance with increasing temperature. It is proposed that testing at higher (above-ambient) temperatures leads to progressive relaxation of the residual stresses in the pipe; this causes the pipe to perform better as residual stresses are known to help accelerate the fracture process. Finally, our investigation indicates no correlation, whatsoever, between brittle failures in pressurized pipes and the PENT (Pennsylvania edge-notch tensile test; ASTM F1473) failure times. Therefore, one has to be extremely cautious in interpreting the true value of the PENT test when developing polymers and pipes for high-performance pressure pipe applications.

Keywords: Pipe; Polyethylene; Fracture

TPO based nanocomposites. Part 1. Morphology and mechanical properties by Hyuk-soo Lee; Paula D. Fasulo; William R. Rodgers; D.R. Paul (pp. 11673-11689).
The relationship between morphology and the mechanical properties of thermoplastic olefin (TPO) materials that are reinforced with organoclay fillers and prepared by melt processing is reported. Nanocomposites based on blends of polypropylene and elastomer and using an organoclay masterbatch were prepared in a twin-screw extruder. Transmission electron microscopy, atomic force microscopy and wide-angle X-ray scattering were employed to carry out a detailed particle analysis of the morphology of the dispersed clay and elastomer phases for these nanocomposites. The improvement in mechanical properties, e.g. stiffness enhancement as evaluated by stress–strain analysis and impact strength obtained from notched Izod impact tests, were successfully explained in terms of morphological changes induced by the presence of the clay and elastomer particles. Quantitative analyses of TEM micrographs and AFM images revealed a decrease in the aspect ratio of the clay particles and a reduction in the size of elastomer particles with increasing clay content. In addition, WAXD scans indicated a skin–core effect for the injection molded specimens in terms of both polypropylene crystal orientation and clay filler orientation. This information is essential for the understanding of the mechanism of mechanical property enhancement in nanocomposite materials.

Keywords: Polymer nanocomposites; Polypropylene; Elastomer

Synthesis and characterization of naphthoxazine functional poly(ε-caprolactone) by Baris Kiskan; Yusuf Yagci (pp. 11690-11697).
A novel naphthoxazine ring-containing poly(ε-caprolactone) (PCL) was synthesized and characterized. For this purpose, first hydroxyl functional naphthoxazine, namely 2-(1 H-naphtho[1,2-e][1,3]oxazin-2-yl)-ethanol (N-a-OH) was prepared by the reaction of 2-naphthol, ethanolamine and paraformaldehyde either in bulk or in dioxane as solvent at 110°C. Subsequently, N-a-OH was used as the coinitiator for the stannous-2-ethylhexanoate (Sn(Oct)2) catalyzed living ring-opening polymerization of ε-caprolactone. The GPC, IR,1H NMR, UV, and fluorescence spectroscopic studies revealed that low-polydispersity PCL with naphthoxazine functionality at the end of the chain was obtained. The resulting PCL macromonomer undergoes thermal curing in the presence of low molar mass benzoxazine (P-a) at various temperatures with the formation of thermosets having PCL segments.

Keywords: Naphthoxazine; Polybenzoxazine; Poly(ε-caprolactone)

Synthesis and characterization of copolymers of 5,6-benzo-2-methylene-1,3-dioxepane and n-butyl acrylate by Jinyu Huang; Roberto Gil; Krzysztof Matyjaszewski (pp. 11698-11706).
The ATRP copolymerization of 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) with n-butyl acrylate ( nBA) was studied by using ethyl 2-bromoisobutyrate (EBriBu) and N, N, N′, N″, N″-pentamethyldiethylenetriamine (PMDETA)/Cu(I)Br as the initiator and catalyst, respectively. The reactivity ratios of the monomers in the copolymerization were determined using the Kelen–Tüdõs method and were found to be rBMDO=0.08 and r nBA=3.7. The copolymer yield decreased with higher amounts of BMDO in the initial feed. The structure of these copolymers was thoroughly characterized by 1D and 2D NMR techniques and quantitative ring opening of BMDO in its copolymerization was demonstrated. The hydrolytic degradation behavior of the BMDO/ nBA copolymers was also studied.

Keywords: Radical ring-opening polymerization; Reactivity ratio; Hydrolytic degradation

Mechanical properties of Nafion™ electrolyte membranes under hydrated conditions by Sumit Kundu; Leonardo C. Simon; Michael Fowler; Stephen Grot (pp. 11707-11715).
Polymer electrolyte membrane fuel cells use a polymer membrane as the electrolyte to transport hydrogen ions from the anode to the cathode side. This paper reports a study of mechanical (stress–strain curves) and dynamic mechanical (temperature sweeps) properties of membranes made using Nafion™ under dry and hydrated conditions. Hydrating the membranes reduced the mechanical properties. Specifically there was significant change in the Young's modulus, yield strength, and transition temperatures of the different membranes tested. Presence of contaminant ions was studied through an ion exchange technique using selected ions (Na+, K+, Mg2+, Cu2+, Ni2+). Ion exchange in hydrated samples increased the stiffness of the material as well as the yield strength in order of increasing ionic radius. Transition onset temperatures observed on the mechanical damping of hydrated membranes also increased with the addition of ions.

Keywords: Nafion™; Mechanical testing; DMTA

Influence of montmorillonite layered silicate on plasticized poly(l-lactide) blown films by Christopher Thellen; Caitlin Orroth; Danielle Froio; David Ziegler; Jeanne Lucciarini; Richard Farrell; Nandika Ann D'Souza; Jo Ann Ratto (pp. 11716-11727).
Plasticized poly(l-lactide) (PLA) montmorillonite layered silicate (MLS) nanocomposites were compounded and blown-film processed using a co-rotating twin screw extruder. PLA was mixed with 10wt% acetyltriethyl citrate ester plasticizer and 5wt% of an organically modified montmorillonite at various screw speeds. Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) determined that the compounded pellets and the blown film PLA/MLS nanocomposites were intercalated. The effect of processing screw speeds on the barrier, thermal, mechanical, and biodegradation properties of the nanocomposites were analyzed and compared to the neat polymer. Nanocomposite films show a 48% improvement in oxygen barrier and a 50% improvement in water vapor barrier in comparison to the neat PLA. The thermogravimetric analysis (TGA) showed an overall 9C increase in the decomposition temperature for all of the nanocomposites. Differential scanning calorimetry (DSC) has determined that the glass transition, cold crystallization and melting point temperatures were not significantly influenced by the presence of MLS. Mechanical properties of the nanocomposites showed that the Young's modulus increased by 20% and the ultimate elongation of the nanocomposites were not sacrificed in comparison to the neat samples. Biodegradation rates in soil were slightly greater for the PLA/MLS nanocomposite than the pure PLA. However, none of the PLA pure and nanocomposites achieved significant biodegradation levels after 180 days.

Keywords: Polylactide; Montmorillonite; Nanocomposites; Biodegradation; Barrier properties

Effects of surface and volume modification of poly(vinylidene fluoride) by polyaniline on the structure and electrical properties of their composites by V.N. Bliznyuk; A. Baig; S. Singamaneni; A.A. Pud; K.Yu. Fatyeyeva; G.S. Shapoval (pp. 11728-11736).
The structure and electrical properties of polyaniline (PANI) modified poly(vinylidene fluoride) (PVDF) films have been studied depending on the type of modification (surface or volume) and the type of dopant (HCl or dodecylbenzenesulfonic acid). The structure was studied with differential scanning calorimetry, atomic force microscopy and Raman spectroscopy (including the surface enhanced mode—SERS) techniques. Surface modification of PVDF with PANI creates a two-dimensional (2D) conductive network on the surface of PVDF films with the thickness of approximately 8μm. The network is characterized with non-linear current voltage ( IV) characteristics and enhanced conductivity at elevated temperatures (up to 160°C), which is opposite to volume modified samples behaviour. Conductivity of the composite films varies in the range of 10−8 to 10−3S/cm depending on the preparation conditions. The observed non-linear conductivity is explained by formation of the surface conductive network of PANI alternated with β-crystalline PVDF microdomains.

Keywords: PVDF–PANI composites; Structure; Non-linear electrical properties

Two-dimensional solid-state NMR studies of crystalline poly(ethylene oxide): Conformations and chemical shifts by D.J. Harris; T.J. Bonagamba; M. Hong; K. Schmidt-Rohr (pp. 11737-11743).
The torsion angles of the OC–CO bonds in crystalline poly(ethylene oxide), PEO, were investigated by solid-state nuclear magnetic resonance (NMR). Two-dimensional double-quantum (DOQSY) spectra indicate that the OC–CO bonds are all gauche with an average torsion angle of ψ=74±4° and a narrow torsion-angle distribution, σ ψ<8°. This is contradictory to the wider range of gauche torsion angles in the distorted helical structure previously proposed based on X-ray fiber diffraction. The low-temperature magic-angle-spinning (MAS)13C NMR spectrum of unlabeled PEO contains four maxima and several shoulders, over a range of 3.1ppm. Deconvolution of this spectrum, together with two-dimensional13C INADEQUATE NMR and exchange MAS spectra, suggests a possible assignment of chemical shifts to the 14 carbons in the 72 helical repeat unit. The small line widths of the individual peaks indicate that the helical repeat unit is accurately replicated throughout the crystals. The results show that packing effects or small conformational differences can change chemical shifts by amounts that had previously been ascribed only to trans/ gauche differences.

Keywords: PEO; Torsion angles; Chemical shift

Relationship between nanoscale deformation processes and elastic behavior of polyurethane elastomers by Elizabeth M. Christenson; James M. Anderson; Anne Hiltner; Eric Baer (pp. 11744-11754).
The cyclic deformation of two polyurethane elastomers that differed in soft segment content and molecular weight was investigated. The microphase-separated morphology of the polyurethane with higher soft segment content consisted of hard segment domains dispersed in a soft segment matrix. In the polyurethane with lower soft segment content, the hard segment domains appeared to be partially cocontinuous. Following an initial ‘conditioning’ cycle, both polyurethanes exhibited reversible elastomeric behavior. Structural changes that occurred during conditioning were investigated using atomic force microscopy and Fourier transform infrared dichroism. The results provided the basis of a structural model for the deformation behavior. Yielding and reorganization of hard domains resulted in a highly oriented microfibrous morphology. Subsequent unloading and reloading were associated with reversible relaxation and reformation of the microfibrous entities. The elastic behavior of the conditioned polyurethanes was satisfactorily described by classical rubber theory with inextensibility. The structural model proposed here extended previous efforts to describe the deformation processes of polyurethanes during cyclic loading.

Keywords: Polyurethanes; Atomic force microscopy; Elastomer

A new turbidimetric approach to measuring polyethylene short chain branching distributions by Colin Li Pi Shan; Willem A. deGroot; Lonnie G. Hazlitt; David Gillespie (pp. 11755-11767).
A new instrument to analyze the short chain branching distribution of polyethylenes has been described. Turbidity analysis of ethylene/α-olefin copolymers by turbidity fractionation analysis can provide short chain branching distribution information that is similar to CRYSTAF and TREF. In these experiments, the turbidity of a polymer solution is monitored while changing its temperature at a controlled rate. The turbidimetric response is to the precipitation or dissolution of the crystallized polymer at a given temperature. With an approach similar to CRYSTAF, the differential of the turbidity profile provides valuable SCBD information for polymers with broad and narrow compositions such as Ziegler-Natta LLDPE and homogeneous polymers catalyzed by single-site catalysts.

Keywords: Polyolefin characterization; Turbidity; Short chain branching distribution

Nanoindentation behavior of ultrathin polymeric films by Kebin Geng; Fuqian Yang; Thad Druffel; Eric A. Grulke (pp. 11768-11772).
Measurement of the mechanical properties of nanoscale polymeric films is important for the fabrication and design of nanoscale layered materials. Nanoindentation was used to study the viscoelastic deformation of low modulus, ultrathin polymeric films with thicknesses of 47, 125 and 3000nm on a high modulus substrate. The nominal reduced contact modulus increases with the indentation load and penetration depth due to the effect of substrate, which is quantitatively in agreement with an elastic contact model. The flow of the nanoscale films subjected to constant indentation loads is shear-thinning and can be described by a linear relation between the indentation depth and time with the stress exponent of 1/2.

Keywords: Polymeric films; Nanoindentation; Viscoelasticity

Structural interpretation of the strain-rate, temperature and morphology dependence of the yield stress of injection molded semicrystalline polymers by J.C. Viana (pp. 11773-11785).
The yield stress of polypropylene specimens with different initial microstructural states is investigated. These latter were obtained by systematic variations of the processing conditions in injection molding, resulting in different laminated skin-core structures. The morphology of the molded specimens was characterized by polarized light microscopy (full specimen), differential scanning microscopy (core layer) and wide-angle X-ray scattering (skin region). The yield stress was evaluated at different nominal strain-rates (1.67×10−3 to 150s−1) and temperatures (23, 40 and 60°C). The experimental results are analyzed in the frame of Eyring's viscous flow and lamellar cluster models, being established the relationships between the activation volume and enthalpy upon the initial morphological state of the specimens. It is proposed that similar deformation mechanisms operate in both skin and core layers, although with distinct temperature and strain-rate sensitivities. The morphology dependence of the yield stress at different temperatures and strain-rates is established in terms of a laminate composite approach. Yielding is interpreted based on the deformation of crystalline lamellae by the pulling out action of both the molecular chains that are anchored in the inter-lamellar amorphous phase and the tie-molecules. The deformation mechanism operating at the skin and core layers are unified by an elastic-beam mechanical analogue that is able of explaining the morphology, temperature and strain-rate dependences of the yield stress.

Keywords: Yield; Morphology; Deformation mechanism

Non-linear, rate-dependent strain-hardening behavior of polymer glasses by Michael Wendlandt; Theo A. Tervoort; Ulrich W. Suter (pp. 11786-11797).
This study is concerned with the finite, large strain deformation behavior of polymeric glasses. True stress–strain curves in uniaxial compression obtained for five different polymeric glasses: polycarbonate, polystyrene, poly(2,6-dimethyl-1,4-phenylene oxide), and linear and cross-linked poly(methylmethacrylate), revealed a strain-hardening response during plastic deformation that is strain-rate dependent and deviates from neo-Hookean behavior. An empirical modification of the so-called compressible Leonov model by a strain dependent activation volume is suggested, which describes the strain-rate dependent large strain behavior of these glassy polymers in good agreement with experimental data.

Keywords: Polymer glasses; Strain?hardening; Activation volume

Rate mechanisms of plasticity in semi-crystalline polyethylene by A.S. Argon; A. Galeski; T. Kazmierczak (pp. 11798-11805).
Based on our experiments on polyethylene where we have observed a constant level of plastic resistance, independent of lamella thickness exceeding 40nm, we have fundamentally re-considered the rate controlling mechanisms of crystal plasticity in semi-crystalline polymers. In this we have not only re-examined and made modifications to the widely accepted mechanism of Young (Young RJ. Mater Forum 1988;11:210.) of monolithic nucleation of screw dislocations from edges of crystalline lamellae predicting an increase in plastic resistance with increasing lamella thickness, but we are proposing here two new modes of nucleation of both edge and screw dislocation half loops from lamella faces that are independent of lamella thickness. These two new modes of dislocation nucleation explain well the observed transition from a plastic resistance increasing with lamella thickness to one of constant resistance above a lamella thickness of ca. 35nm in polyethylene. They also provide a more satisfactory framework to explain the temperature and strain rate dependence of the plastic resistance of polyethylene and predict the observed levels of activation volumes determined by us.

Keywords: Dislocation nucleation modes; Rate dependent plasticity; Polyethylene

Thermally stimulated recovery of plastic strain in crosslinked and uncrosslinked epoxy/amine systems by Hiroshi Kawakami; Hiroshi Yamanaka; Yukuo Nanzai (pp. 11806-11813).
Effects of crosslinks on plastic strain recovery in epoxy glass was studied by means of thermally stimulated strain recovery (TSSR) and differential scanning calorimetry (DSC) techniques. Two types of samples were prepared from bisphenol-A type epoxide monomer: one had a crosslinked structure cured by 4,4′-diaminodiphenylmethane and the other had a linear uncrosslinked structure polymerized by aniline. Both specimens were compressed first in the rubbery state and subsequently compressed further in the glassy state. After compressed in the glassy state, the specimens were subjected to the TSSR and the DSC measurements. The TSSR results indicated that the amount of plastic strain recovering at temperatures below the glass transition temperature Tg was larger for the crosslinked sample than for the linear sample. On the other hand, the DSC results indicated that the amount of exothermic heat flow at temperatures below Tg was less for the crosslinked sample than for the linear sample. These results presumably indicate that, for the crosslinked epoxy glass deformed in the glassy state, glass-like strain recovers quite cooperatively with rubber-like strain at temperatures below Tg, in contrast to independent recovery of these strains in the linear epoxy glass.

Keywords: Epoxy glass; Differential scanning calorimetry; Thermally stimulated deformation recovery

Miscibility and crystallization behavior of biodegradable blends of two aliphatic polyesters. Poly(3-hydroxybutyrate- co-hydroxyvalerate) and poly(ε-caprolactone) by Zhaobin Qiu; Wantai Yang; Takayuki Ikehara; Toshio Nishi (pp. 11814-11819).
Biodegradable polymer blends of poly(3-hydroxybutyrate- co-hydroxyvalerate) (PHBV) and poly(ε-caprolactone) (PCL) blends were prepared with the ratio of PHBV/PCL ranging from 80/20–20/80 by co-dissolving the two polyesters in chloroform and casting the mixture. Differential scanning calorimetry (DSC) and optical microscopy (OM) were used to investigate the miscibility and crystallization of PHBV/PCL blends. Experimental results indicated that PHBV showed no miscibility with PCL for PHBV/PCL blends as evidenced by the existence of unchanged composition independent glass transition temperature and the biphasic melt. Crystallization of PHBV and PCL was studied with DSC and analyzed by the Avrami equation by using two-step crystallization in the PHBV/PCL blends. The crystallization rate of PHBV at 70°C decreased with the increase of PCL in the blends, while the crystallization mechanism did not change. In the case of the isothermal crystallization of PCL at 42°C, the crystallization rate increased with the addition of PHBV, and the crystallization mechanism changed, too, indicating that the crystallization of PHBV at 70°C had an apparent influence on the crystallization of PCL at 42°C.

Keywords: Poly(3-hydroxybutyrate-; co; -hydroxyvalerate)/poly(ε-caprolactone) blends; Miscibility; Crystallization

Effects of polyoxyethylene nonylphenol on dynamic mechanical properties and crystallization of polypropylene by Qing-Xin Zhang; Jian-Bin Song; Shu-Yun Wang; Zhi-Shen Mo (pp. 11820-11828).
Polypropylene (PP) was blended with polyoxyethylene nonylphenol (PN) in a twin-screw extruder and injection moulded. The dynamic mechanical properties of PP/PN blends were characterized by dynamic mechanical analyser (DMA). The glass transition temperature ( Tg) of PP showed a slight decrease with incorporation of PN. Differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarized optical microscopy (POM) were employed to investigate the effects of PN on crystallization of PP. In a study of nonisothermal crystallization of PP and PP/PN blends, crystallization parameter analysis showed the addition of PN reduced the peak temperature of crystallization. β-form crystals of PP coexisted with α-form crystals in PP/PN blends, and oriented on the surface layer of injection moulded bar as revealed by WAXD. The degree of orientation was determined using Hermans orientation function. The thermal stability of β-form crystals was evaluated using high temperature WAXD and POM.

Keywords: Polypropylene; Polyoxyethylene nonylphenol; Crystallization

Compatibilization-like effect of reactive organoclay on the poly(l-lactide)/poly(butylene succinate) blends by Guang-Xin Chen; Hun-Sik Kim; Eung-Soo Kim; Jin-San Yoon (pp. 11829-11836).
The morphology of an incompatible polymer blend composed of poly(l-lactide) (PLLA) and poly(butylene succinate) (PBS) was examined by scanning and transmission electron microscopy, X-ray scattering, and X-ray photoelectron spectroscopy before and after the incorporation of an organoclay containing reactive functional groups, namely twice functionalized organoclay (TFC). TFC was prepared by treating Cloisite® 25A with (glycidoxypropyl)trimethoxy silane. When a small amount of TFC was incorporated into the PLLA/PBS blend, the clay layers became fully exfoliated and were located mainly in the PLLA phase. At the low clay content, the dispersed phase had an almost constant domain size comparing with the PLLA/PBS blend, which decreased sharply as the clay content was further increased. When the clay content became high, the clay layers were dispersed not only in the PLLA phase but also in the PBS phase with intercalated/exfoliated coexisting morphology. The reactive TFC was found to play an important role in the blend similar to the in situ reactive compatibilizer. The specific interaction between the TFC and the polymer matrix was quantified by the Flory–Huggins interaction parameter, B, which was determined by combining the melting point depression and the binary interaction model. The morphology of the PLLA/PBS/clay composites was analyzed by considering the interaction parameter.

Keywords: Blend; Epoxy groups; Poly(; l; -lactide)

Correlation between crystallization kinetics and melt phase behavior of crystalline–amorphous block copolymer/homopolymer blends by Jen-Yung Hsu; Bhanu Nandan; Mei-Chun Chen; Fang-Choyu Chiu; Hsin-Lung Chen (pp. 11837-11843).
We show that the phase behavior of the strongly segregated blend consisting of a crystalline–amorphous diblock copolymer (C- b-A) and an amorphous homopolymer (h-A), which depends on the degree of wetting of A blocks by h-A, can be probed by the crystallization kinetics of the C block. A lamellae-forming poly(ethylene oxide)- block-polybutadiene (PEO- b-PB) was blended with PB homopolymers (h-PB) of different molecular weights to yield the blends exhibiting ‘wet brush’, ‘partially dry brush’, and ‘dry brush’ phase behavior in the melt state. The crystallization rate of the PEO blocks upon subsequent cooling, as manifested by the freezing (crystallization) temperature ( Tf), was highly sensitive to the morphology and spatial connectivity of the microdomains governed by the degree of wetting of PB blocks. As the weight fraction of h-PB reached 0.48, for instance, Tf experienced an abrupt rise as the system entered from the wet-brush to the dry-brush regime, because the crystallization in the PEO cylindrical domains in the former required very large undercooling due to a homogeneous nucleation-controlled mechanism while the process could occur at the normal undercooling in the latter since PEO domains retained lamellar identity with extended spatial connectivity. Our results demonstrate that as long as the C block is present as the minor constituent the melt phase behavior of C- b-A/h-A blends can also be probed using a simple cooling experiment operated under differential scanning calorimetry (DSC).

Keywords: Crystallization kinetics; Block copolymer blends; Melt phase behavior

Effects of crystallinity and crosslinking on the thermal and rheological properties of ethylene vinyl acetate copolymer by Y.T. Sung; C.K. Kum; H.S. Lee; J.S. Kim; H.G. Yoon; W.N. Kim (pp. 11844-11848).
Effects of crosslinking and crystallinity on the properties of the thermal and rheological properties of the EVA were studied. From the studies of storage modulus of the EVA with VA content in the solid temperature range (about −70 to 50°C), the storage modulus decreased with increasing the VA content. This result suggested that the crystallinity of the EVA affected the storage modulus of the EVA because of the weak crosslinking of the EVA by DCP. From the studies of complex viscosity of the EVA with and without DCP in the melt state, the values of the power law parameter of the EVA without DCP ranged from 0.39 to 0.50 and the EVA with DCP ranged from 0.03 to 0.12. In the measurement of the complex viscosity of the EVA in the melt state, the crosslinking affected the complex viscosity of the EVA with DCP.

Keywords: Ethylene vinyl acetate copolymer; Crystallinity; Crosslinking

Polyurethane elastomers through multi-hydrogen-bonded association of dendritic structures by Chih-Ping Chen; Shenghong A. Dai; Huey-Ling Chang; Wen-Chiung Su; Tzong-Ming Wu; Ru-Jong Jeng (pp. 11849-11857).
A series of hydrogen bonding-rich polyurea/malonamide dendrons have been utilized as building blocks for the synthesis of novel dendritic polyurethane elastomers. Based on the resulting microstructure of soft segments reinforced by the rigid dendritic domains, the hydrogen bonding enforced phase separation of segmented polyurethanes was explored. DSC and FT-IR results indicate that a certain degree of phase separation between dendritic and poly(tetramethylene oxide) (PTMO) domains. The domain size of phase separation are less than 100nm based on the results obtained from the atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). The analysis of tensile measurements indicates that the incorporation of various contents of different dendrons as the hard segments allows these polymers to exhibit drastically different mechanical properties. Furthermore, low complex viscosity is observed at medium temperatures (above 130C) via the rheological analysis. With good mechanical properties at room temperature and low melt viscosity at medium temperatures, these thermoplastic elastomeric polyurethanes are suitable for applying in hot-melt process.

Keywords: Dendrimer; Hydrogen bond; Polyurethane

Optimized species growth in epoxy polymerization with real-coded NSGA-II by Saptarshi Majumdar; Kishalay Mitra; Sasanka Raha (pp. 11858-11869).
Satisfaction of twin objectives of maximization of Mn along with minimization of PDI do not necessarily guarantee the maximization of concentration of desired species in a semibatch epoxy polymerization process. As the final product consists of a number of polymer species, a need is felt to perform an advanced optimization study to come up with such process conditions for which the selective growth of a particular polymer species is maximized in minimum possible processing time and the population of other species should be at their lowest values. These above-mentioned conflicting objectives frame the platform for a multi-objective optimization problem, which is solved here using a real-coded non-dominated sorting genetic algorithm or NSGA II and Pareto optimal solutions are obtained. The decision variables are discrete addition rates of various ingredients, e.g. the amount of addition of bisphenol-A (a monomer), sodium hydroxide and epichlorohydrin at different time steps. All species balance equations, bounds on Mn, PDI and addition amounts are treated as constraints. Results are very promising in terms of optimized operations for selective enhancement of desired polymer species for the epoxy polymerization process. Total additions are kept very close to available experimental conditions to minimize probable extrapolation errors. It has been observed that preferential oligomer production is extremely difficult for epoxy polymerization. Lower chain polymers are the only choice for a good quality, stable polymer product.

Keywords: Epoxy; Selective growth; Kinetics

Hysteretic thermal behavior of amorphous semi-aromatic polyamides by S. Moisa; G. Landsberg; D. Rittel; J.L. Halary (pp. 11870-11875).
The hysteretic thermal behavior of two amorphous semi-aromatic polyamides, subjected to cyclic loading at high stress levels, has been investigated. The two polymers, called 1I and 1.8T, were selected with regards to chain mobility and plastic deformability considerations. This work reports the exothermal response of these materials to high level cyclic stress (of the order of σy), with emphasis on the initial thermal peak, normally observed in commercial polycarbonate (PC) and not in commercial polymethylmethacrylate (PMMA). The investigated materials exhibit noticeable initial thermal peaks, which are similar, to some extent, to those observed in PC. The present results suggest that chain mobility may indeed be partially responsible for the initial exothermal peak, thus supporting the hypothesis that it may be related to the transition from shear deformation zones to chain disentanglement crazing.

Keywords: Hysteretic heating; Cyclic loading; Plastic deformation

Pressure induced order–disorder transition in a diblock copolymer by Onkar Prasad; Leena Sinha; Neeraj Misra; Govind P. Gupta; Ramesh C. Agnihotri (pp. 11876-11880).
Polymers are known to undergo order↔order and order↔disorder transitions, when subjected to a change of pressure, temperature, solvent, pH of the medium etc. The molecular processes, which alter the volume of the system, are found to be highly sensitive to the pressure. In the present communication Zimm and Bragg model of helix↔coil transition has been modified to interpret the experimental data of pressure induced phase transition in polystyrene–polybutadiene [PS–PB] at different pressurization rates, as reported by Migler and Han, utilizing the Birefringence and small angle neutron scattering technique. An expression for the degree of order is obtained from the grand partition function for the entire chain in terms of nucleation parameter, which controls the transition width. The nucleation parameter σ increases with the increase in the ODT temperatures of the system. The phenomenon of hysteresis has been discussed in relation to the pressurization rate, which increases/decreases with the corresponding increase/decrease in the pressurization rate. The theoretical transition curves are found to be in good agreement with experimental data.

Keywords: Phase transition; Pressure; Copolymer

Molecular dynamics simulation of liquid crystal formation within semi-flexible main chain LCPs by Kai Leung Yung; Lan He; Yan Xu; Yun Wen Shen (pp. 11881-11888).
Molecular dynamics simulations of a semi-flexible main chain LCP (liquid crystalline polymer) have been carried out using a newly developed model named solo-LJ-spring-GB model. The new model represents the molecular chain in the form of GB-spring-LJ-spring-…-LJ-spring-GB sections that simplifies the model and reduces the simulation computation by many times. The new model was evaluated by studying the phase behaviors of semi-flexible main chain LCPs through simulation. The results, such as the spontaneous phase transition from isotropic phase to nematic phase as the system temperature decreases and the odd–even effect of the number of flexible spacers on its thermodynamic properties agree well with other experimental results as well as simulations using the traditional GB/LJ model. The orientational and translational mobilities of mesogenic units in the new model have also been measured and compared with those in the traditional GB/LJ model with very little differences found.

Keywords: Liquid crystalline polymers; Solo-LJ-spring-GB model; Molecular dynamics simulation

Molecular modeling and synthesis of polymers for use in applications requiring a low-k dielectric by Gary W. Beall; Suresh Murugesan; Heather C. Galloway; Deborah C. Koeck; Jeremy Jarl; Francine Abrego (pp. 11889-11895).
As integrated circuits have become more and more complex and with smaller and smaller feature sizes several limitations have become apparent. One of these is the need for low-k dielectric materials as insulating layers. Recent work has reported promising materials for such insulators that include some fluorinated polymers. These dielectric materials were further improved by introducing porosity into the polymer films. One of the key factors in the dielectric constant of a material is its density. As the polarization of the material is related to the number of bonds, the dielectric constant will scale with the density. In this paper a series of molecular modeling calculations were conducted on various fluorine substituted polymers in order to predict their densities. A surprising result of these calculations was the prediction that some of the polymers would have densities less than 1g/cm3. One of these polymers was synthesized and the density determined. The calculated density was in extremely good agreement with the experimental density. This paper will present the details of the molecular modeling technique as well as the synthesis and characterization of one of the polymers of interest.

Keywords: Low-k dielectrics; Polymer densities; Molecular modeling

Constitutive modeling for mechanical behavior of PMMA microcellular foams by Choonghee Jo; Jin Fu; Hani E. Naguib (pp. 11896-11903).
Constitutive equations for nonlinear tensile behavior of PMMA foams were studied. Five viscoelastic models composed of elastic and viscous components were accounted for the modeling of the constitutive equations. The developed constitutive equations are expressed in terms of material properties and foam properties such as strain, strain rate, elastic modulus, relative density of foam, and relaxation time constant. It was found that the stress–strain behaviors by Generalized Maxwell model, Three Element model and Burgers model could be described by the constitutive equation obtained from the Maxwell model. For the verification of the constitutive model, poly(methyl methacrylate) (PMMA) microcellular foams were manufactured using batch process method, and then uniaxial tensile tests were performed. The stress–strain curves by experiment were compared with the theoretical results by the constitutive equation. It was demonstrated that nonlinear tensile stress–strain behaviors of PMMA foams were well described by the constitutive equation.

Keywords: Constitutive equation; Nonlinear viscoelastic model; PMMA microcellular foam

A unified approach to conformational statistics of classical polymer and polypeptide models by Jin Seob Kim; G regory S. Chirikjian (pp. 11904-11917).
We present a unified method to generate conformational statistics, which can be applied to any of the classical discrete-chain polymer models. The proposed method employs the concepts of Fourier transform and generalized convolution for the group of rigid-body motions in order to obtain probability density functions of chain end-to-end distance. In this paper, we demonstrate the proposed method with three different cases: the freely rotating model, independent torsion-angle energy model, and interdependent pair-wise energy model (the last two are also well-known as the rotational isomeric state model). As for numerical examples, for simplicity, we assume homogeneous polymer chains. For the freely rotating model, we verify the proposed method by comparing with well-known closed-form results for mean-squared end-to-end distance. In the interdependent pair-wise energy case, we take polypeptide chains such as polyalanine and polyvaline as examples.

Keywords: Conformational statistics; Rigid-body motion group; Non-commutative harmonic analysis

Monte Carlo simulation of chain extension using bisoxazolines as coupling agent by Li-Tang Yan; Zhen-Yu Qian; Bao-Hua Guo; Jun Xu; Xu-Ming Xie (pp. 11918-11926).
The chain extension using bisoxazolines (OO) as coupling agent was studied by means of the Monte Carlo (MC) method, focusing on the reaction kinetics. A comparison between simulated results and those calculated by an improved kinetic model was made. The coupling efficiency of the chain extender, average molecular weight and molecular weight distributions (MWDs) were investigated. The results show that the biggest coupling efficiency, the highest average molecular weight and the narrowest MWDs can be obtained when the initial concentrations of carboxyl and oxazoline groups are equal. The results indicate that higher activity difference between the oxazoline group in OO and that in blocked CA can lead to higher average molecular weight and narrower MWDs. Those results are in good agreement with the experiments. Besides above factors, diffusion effect and degradation effect are important factors for the average molecule weight and MWDs. And lower reaction kinetics constants of diffusion effect and degradation effect both result in a higher number-average molecular weight(Mn). The results also indicate that two peaks, at the different molecular weight, appear in the curve of molecular weight distributions during chain extension reaction. The variation of these two peaks corresponds to different polydispersities.

Keywords: Chain extension; Monte Carlo simulation; Kinetics

Synthesis and properties of poly(arylenevinylene)s comprising of an electron-donating carbazole unit and an electron-accepting 2,1,3-benzothiadiazole (or fluorenone) unit in the main chain by Junping Du; Qiang Fang; Xiaoyao Chen; Shijie Ren; Amin Cao; Bing Xu (pp. 11927-11933).
Two new soluble arylenevinylene-based polymers comprising of an electron-donating carbazole unit and an electron-accepting 2,1,3-benzothiadiazole (or fluorenone) unit in the main chain were synthesized by Heck polycondensation between 3,6-divinylene-9-decyl carbazole and 4,7-dibromo-2,1,3-benzothiadiazole (or 2,7-dibromofluorenone). In the toluene solution, a polymer with benzothiadiazole unit showed strong red photoluminescence, whereas the polymer with fluorenone unit showed white–yellow photoluminescence. The polymers had good thermal stability with 5wt% loss temperature of more than 430°C. Electrochemically, the polymers appeared to be reversible under reduction.

Keywords: Arylenevinylene derivatives; Poly(; p; -phenylenevinylene)s; Carbazole derivatives

Host/guest complex of Me- β-CD/2,2-dimethoxy-2-phenyl acetophenone for initiation of aqueous photopolymerization: Kinetics and mechanism by ShuJing Li; FeiPeng Wu; MiaoZhen Li; ErJian Wang (pp. 11934-11939).
Methylated- β-cyclodextrin (Me- β-CD) was used to complex the photoinitiator, 2,2-dimethoxy-2-phenyl acetophenone (DMPA), yielding a water-soluble host/guest complex. The comparative studies demonstrated that the Me- β-CD complexed DMPA exhibited a high photoreactivity identical to the uncomplexed DMPA, while the CD complex obviously influenced the products of primary photolysis of DMPA and the photopolymerization kinetics due to the steric effect of CD on the subsequent initiation reactions. The photopolymerization rate of acrylamide can be described by the equation: Rp= K[2a]0.62[M]1.37[I]0.5[Me- β-CD]0. The mechanism of polymerization was also discussed.

Keywords: Host/guest complex; Cyclodextrin; Kinetics

Synthesis of novel poly{methyl-[3-(9-indolyl)propyl]siloxane}-based nonlinear optical polymers via postfunctionalization by Zhen Li; Jianli Hua; Qianqian Li; Cheng Huang; Anjun Qin; Cheng Ye; Jingui Qin (pp. 11940-11948).
A novel series of nonlinear optical (NLO) polysiloxanes with a high density of chromophore moieties based on poly{methyl-[3-(9-indolyl)propyl]siloxane} (PMIPS) were synthesized by a post functional strategy. First, PMIPS (P1) was prepared through hydrosilylation reaction, thenP1 is partially formylated by the reaction betweenP1 and the reagents of dimethylformamide (DMF) and phosphorus oxychloride under the standard Vilsmeier reaction conditions, and these formyl groups with high reactivity are condensed with four predesigned cyanoacetylated chromophores to afford the series of chromophore functionalized polysiloxanes (P36). The most special point is the molar concentrations of chromophore moieties are the same in polymersP36, which makes it convenient to study the behavior of different chromophores in the polymeric system. The poled films ofP36 reveal the resonant d33 values in the range of 7.9–55.2pm/V by second harmonic generation (SHG) measurements.

Keywords: Polysiloxane; Synthesis; Indole

A novel aromatic polyimide with rigid biphenyl side-groups: Formation and evolution of structures in thermoreversible gel by Xiangyang Liu; Linghong Guo; Yi Gu (pp. 11949-11957).
A new thermoreversible polyimide gel was prepared and characterized. This polyimide was synthesized from 4,4′-oxydiphthalicanhydride (ODPA) and 3,5-diamino-benzonic-4′-diphenyl ester (DABBE) via a one-step polymerization procedure in m-cresol. With lowering temperature, a gel from the polyimide (PI) solution was formed due to the solvation power decrease. On heating, a gel/sol transition could be observed by an endothermic peak of DSC curve, and the gel/sol transition enthalpy and temperature went up with the increase of the solution concentration. The original aggregation structure of the gel is amorphous. While the gel was kept at 15°C, two kinds of order structure developed, which were determined by X-ray. One was layer structure which formed from aggregations of main chains with d-spacing of 15.7Å (2 θ=5.64°) or from side chains with d-spacing of 36.6Å (2 θ=2.41°); The other was crystallosolvate region formed within aggregation of main chains (2 θ=10–35°), and the kinetics of isothermal crystallosolvate was analyzed by means of the Avirami equation. At the same time, a possible chain-packing model was suggested. Based on X-ray, DSC and FTIR experiments, the evolution of the ordered structure was also investigated in detail. The results imply that the hydrogen bonding interactions exist between solvent molecule and macromolecule, which is a possible mechanism of the formation of the above gels and order structures.

Keywords: Polyimide; Gel/sol transition; Layer structure

Preparation and characterization of three-dimensionally ordered macroporous syndiotactic poly( p-methylstyrene) by Xu Zhang; Weidong Yan; Haiqing Li; Xiaoli Shen (pp. 11958-11961).
Three-dimensionally ordered macroporous(3DOM) syndiotactic poly( p-methylstyrene) (sPPMS) with pore size 170nm was fabricated by means of silica templates using (dbm)2Ti(OPh)2/MAO catalytic system. The resulting polymers were characterized by SEM,13C NMR, DSC and GPC. The results indicated that the 3DOM sPPMS were highly syndiotactic. GPC curves showed that the 3DOM sPPMS possessed lower Mn and broader MWD compared with bulk one. Meanwhile, DSC results revealed that three 3DOM sPPMS exhibited crystalline form II, and bulk sPPMS form III.

Keywords: Dimensionally ordered macroporous polymer; Syndiotactic poly(; p; -methylstyrene); Coordination polymerization

Long-tailed spherical aggregates formed from ABA triblock copolymer by changing the properties of selective solvent by Jintao Zhu; Haizhou Yu; Wei Jiang (pp. 11962-11968).
A convenient method of tuning aggregate morphologies from amphiphilic block copolymer by adding second selective solvent is introduced in this paper. Some novel aggregate morphologies, i.e. hierarchical vesicles (and compound spherical micelles) with one or more tails, were formed by introducing a second selective solvent for core-forming blocks into the poly(4-vinyl pyridine)- b-polystyrene- b-poly(4-vinyl pyridine) ABA amphiphilic block copolymer/co-solvent/water systems. Addition of selective solvent (toluene) for core-forming blocks (PS blocks) has significant effect on the aggregate morphologies from the amphiphilic triblock copolymer. The aggregate morphologies changed from spheres to rods, long tailed solid large compound spheres, and to long tailed hierarchical vesicles by adding 0.5, 10 and 30wt% of toluene to the organic solvent, respectively. There exists an aggregate morphological transition of the long tailed hierarchical vesicles to long tailed solid spheres by decreasing the content of toluene in the organic solvent mixture. The tails disappeared, and irregular vesicular and spherical structures were formed when the toluene content was 20wt%. The toluene addition is expected to increase the stretching of the core-forming blocks (PS), and to modify the interfacial tension of core–corona interface, which are the main reasons for the aggregate morphology transition. To the best of our knowledge, these tailed vesicles and spherical morphologies have not been found in block copolymer aggregates system up to now.

Keywords: Amphiphilic block copolymer; Micelles; Selective solvent

Nanoindentation and morphological studies on injection-molded nylon-6 nanocomposites by Lu Shen; Wuiwui Chauhari Tjiu; Tianxi Liu (pp. 11969-11977).
The nanoindentation behavior and morphology of the injection-molded specimens of nylon-6 (PA6)/clay nanocomposites prepared by melt-compounding have been studied in present study. The elastic and plastic properties as well as creep behavior of PA6 and its nanocomposites are comparatively evaluated as the function of clay loading by using nanoindentation technique. The anisotropic characteristics in mechanical properties are studied by indenting the injection-molded specimens in two different directions (i.e. parallel and perpendicular to the injection direction). The uneven distribution of both the clay nanofiller and the crystallinity of the polymeric matrix induced by melt-processing leads to the variation of the mechanical property of the nanocomposites in certain directions and locations within the molded specimens. The microstructural and morphological changes of PA6 upon incorporating with clay nanofiller are evidenced by transmission electron microscopy and small-angle X-ray scattering, which are closely correlated with the anisotropy of the mechanical properties observed by nanoindentation.

Keywords: Nylon-6; Nanocomposites; Nanoindentation

Isothermal crystallization of intercalated and exfoliated polyethylene/montmorillonite nanocomposites prepared by in situ polymerization by Jun-Ting Xu; Yan-Qin Zhao; Qi Wang; Zhi-Qiang Fan (pp. 11978-11985).
Polyethylene/montmorillonite (PE/MMT) nanocomposites with different dispersion states of MMT were prepared by in situ polymerization. Isothermal crystallization of the intercalated nanocomposite, in which the PE chains were confined in the MMT layers, was studied and was compared with that of the exfoliated nanocomposite. It is observed that the intercalated sample has longer induction period, longer crystallization half time and larger crystallization activation energy than the exfoliated sample, showing that crystallization of PE is retarded due to confinement of the MMT layers. Analysis of crystallization kinetics shows that Avrami exponent ( n) increases gradually with crystallization temperature. However, the maximal value of n is 2.0 for the intercalated sample, but it can reach 3.0 for the exfoliated sample. It is inferred that the stems of the PE crystals confined in the MMT layers are parallel to the MMT layers. The Hoffman–Weeks extrapolation method cannot be applied in the intercalated sample because of the small lateral surface of the PE crystals. Based on the depression of the melting temperature, the specific free energy of the PE/MMT interface was estimated, which is about 1.0mJ/cm2, much smaller than the free energy of the lateral surface of PE crystals. This is attributed to the origin of the strong nucleation effect of MMT.

Keywords: Polyethylene; Crystallization; Nanocomposite

Synthesis and properties of novel polyimides derived from 2,6-bis(4-aminophenoxy-4′-benzoyl)pyridine with some of dianhydride monomers by Shujiang Zhang; Yanfeng Li; Xiaolong Wang; Xin Zhao; Yu Shao; Daxue Yin; Shiyong Yang (pp. 11986-11993).
A new kind of aromatic diamine monomer containing pyridine unit, 2,6-bis(4-aminophenoxy-4′-benzoyl)pyridine (BABP), was synthesized successfully. The Friedel–Crafts acylation of phenyl ethyl ether with 2,6-pyridinedicarbonyl chloride formed 2,6-bis(4,4′-dihydroxybenzoyl)-pyridine (BHBP), BHBP was changed into 2,6-bis(4-nitrophenoxy-4′-benzoyl)-pyridine (BNBP) by the nucleophilic substitution reaction of it and p-chloronitrobenzene, and BNBP was reduced with SnCl2 and HCl in ethanol to form the diamine monomer BABP finally, the diamine monomer BABP could be obtained in quantitative yield. A series of novel polyimides were prepared by polycondensation of BABP with various aromatic dianhydrides in N-methy-2-pyrrolidone (NMP) via the conventional two-step method. Experimental results indicated that some of the polyimides were soluble both in strong dipolar solvents ( N-methy-2-pyrrolidone or N, N-dimethylacetamide) and in common organic solvents tetrahydrofuran. The resulting polyimides showed exceptional thermal and thermooxidative stability, no weight loss was detected before a temperature of 450°C in nitrogen, and the values of glass-transition temperature of them were in the range of 208–324°C. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.

Keywords: Pyridine-containing polyimides; Synthesis; Thermostablity

Moisture sorption–desorption–resorption characteristics and its effect on the mechanical behavior of the epoxy system by Y.C. Lin; Xu Chen (pp. 11994-12003).
Thermosetting epoxy resins are attractive materials for many engineering applications, as they are low in density, with excellent mechanical properties and easily fabricated by processes such as injection molding, extrusion and vacuum forming. However, the hostile hygrothermal environment can degrade the epoxy system. In this study, moisture sorption–desorption–resorption characteristics of the DGEBA/DDA epoxy system have been investigated by the hygrothermal aging and molecular dynamic (MD) simulation. Also, the effects of moisture on the mechanical behavior of the epoxy system have been studied by the uniaxial tensile test and a scanning electron microscopy (SEM), for the unaged, moisture saturated, completely desorbed and moisture re-saturated specimens, respectively. Results show that the moisture diffusion in epoxy system is not only dependent on the hygrothermal conditions, but also on the specimen thickness and hygrothermal history. Due to the effect of the hygrothermal aging, both the tensile elastic module and tensile strength of the studied epoxy system have been reduced, that is, the absorbed moisture has deleterious effects on the physical properties of epoxies and can, therefore, greatly compromise the performance of an epoxy-based component.

Keywords: Epoxy; Hygrothermal aging; Mechanical properties

Formation of cylindrical phase structure in PMMA/HBP polymer blend films by Li Yao; Xie Xuming; Zong Qi; Tang Liming (pp. 12004-12009).
The evolution of the phase separation was investigated for poly(methyl methacrylate)(PMMA)/hyperbranched poly(ester-amide)(HBP) blend films on glass substrate by means of phase contrast microscopy. The films with different component ratios show different phase separation processes and phase morphologies. At a film thickness of about several hundreds nanometers, a cylindrical dispersed phase was observed in the films with lower HBP content. The effects of the composition and sample thickness on the formation of the special morphology were also studied. It is found that the interaction between the substrate and HBP and the thickness of blend film are essential factors for the formation of the phase morphology and the appearance of the special cylindrical morphology depends on the component ratio and the film thickness. There is a critical film thickness, above which the special morphology could be observed. The critical thickness varies as the HBP weight percent changes. Our research provides a possible strategic way to obtain polymer films with special structure which are important for an increasing number of applications in wide fields.

Keywords: Blend films; Cylindrical structure; Hyperbranched poly(ester-amide)

Synthesis and properties of a novel water-soluble anionic polyfluorenes for highly sensitive biosensors by Fei Huang; Xiaohui Wang; Deli Wang; Wei Yang; Yong Cao (pp. 12010-12015).
A new anionic water-soluble polyfluorene—poly(9,9-bis(4′-sulfonatobutyl)fluorene- co- alt-1,4-phenylene) sodium salt (PFS) was synthesized by Suzuki-coupling reaction. The anionic polyfluorene shows bright blue photoluminescence and it was found the photoluminescence could be highly quenched by a bioactive dye (Lucifer yellow cadaverine biotin-X dipotassium salt). PFS photoluminescence quenching only occurs effectively upon addition of avidin. The photoluminescence quenching process is sensitive to even subnanomolar amount of avidin (10−10M). The avidin facilitated photoluminescence quenching opens up opportunities of new ultra-high efficiency and rapid response biosensors based on the polyfluorene electrolyte.

Keywords: Polyelectrolyte; Water-soluble; Biosensor

Epoxy nanocomposites with octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane by Yonghong Liu; Sixun Zheng; Kangming Nie (pp. 12016-12025).
The POSS-containing nanocomposites of epoxy resin were prepared via the co-curing reaction between octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane (OpePOSS) and the precursors of epoxy resin. The curing reactions were started from the initially homogeneous ternary solution of diglycidyl ether of bisphenol A (DGEBA), 4,4′-Diaminodiphenylmethane (DDM) and OpePOSS. The nanocomposites containing up to 40wt% of POSS were obtained. The homogeneous dispersion of POSS cages in the epoxy matrices was evidenced by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and atomic force microscopy (AFM). Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that at the lower POSS concentrations (<30wt%) the glass transition temperatures ( Tgs) of the nanocomposites almost remained invariant whereas the nanocomposites containing POSS more than 40wt% displayed the lower Tgs than the control epoxy. The DMA results show that the moduli of the nanocomposites in glass and rubbery states are significantly higher than those of the control epoxy, indicating the nanoreinforcement effect of POSS cages. Thermogravimetric analysis (TGA) indicates that the thermal stability of the polymer matrix was not sacrificed by introducing a small amount of POSS, whereas the properties of oxidation resistance of the materials were significantly enhanced. The improved thermal stability could be ascribed to the nanoscaled dispersion of POSS cages and the formation of tether structure of POSS cages with epoxy matrix.

Keywords: Epoxy resin; Polyhedral oligomeric silsesquioxane; Nanocomposites

States of water in partially swollen poly(vinyl alcohol) hydrogels by Wenbo Li; Feng Xue; Rongshi Cheng (pp. 12026-12031).
A poly(vinyl alcohol) hydrogel was prepared by coupling poly(vinyl alcohol) with epichlorohydrin as cross-linking agent. Various amounts of water were added into the dry hydrogel to swell it and the quantity of water in various states in the partially swollen hydrogel were determined by DSC ice-melting technique. A parameter S denoted the degree of the saturation of swelling was introduced for describing the various stages of water absorption. The analytical results indicate that there exists two critical threshold degree of saturation. At the first threshold S*, the freezable bound water starts to appear and at the second threshold S**, the free water begins to appear. In the region of S< S*, the adsorbed water exists only in the non-freezable form and increases linearly with S until reaching S*. The sum of non-freezable and freezable bound water consists of the hydration layer around the chain segments of the network. The hydration number HN of the repeating unit of PVA hydrogel increases from zero to a limiting value about 2.5 as the degree of saturation varies from zero to one.

Keywords: DSC; States of water; Saturation of swelling

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