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European Polymer Journal (v.41, #1)

Kinetic simulation of living carbocationic polymerizations. II. Simulation of living isobutylene polymerization using a mechanistic model by Judit E. Puskas; Sohel Shaikh; Kevin Z. Yao; Kim B. McAuley; Gabor Kaszas (pp. 1-14).
This paper discusses the kinetic simulation of TiCl4––coinitiated living carbocationic isobutylene (IB) polymerizations governed by dormant-active equilibria, using a mechanistic model. Two kinetic models were constructed from the same underlying mechanism: one using a commercial simulation software package (Predici®), and the other using the method of moments. Parameter estimation from experimental batch reactor data with Predici yielded a rate constant of propagation kp=4.64×108±2.75×108L/mols, with no constraints imposed. This agrees with kp data measured with diffusion clock and competition methods, but disagrees with kinetically obtained kp values. Estimation of rate constants with Predici® and the GREG parameter estimation software packages revealed that it was difficult to estimate the complete set of kinetic parameters, due to correlated effects of the parameters on model predictions. Estimability analysis confirmed that some of the strongly correlating parameters could not be estimated simultaneously using the available experimental data. Using kp=6×108±2.75×108L/mols measured by Mayr, and using starting estimates of other rate constants defined by experimentally observed correlations, yielded the set of rate constants required for the simulations. Both kinetic models yielded good agreement with experimental data, with the exception of Mw values that slightly diverged from the theoretically predicted ‘ MwMn=constant’ relationship. This may indicate the occurrence of a minor side reaction. However, the kp/ k−1=17.5L/mol average run length calculated from measured and simulated MWD data agrees well with earlier literature values.

Keywords: Living carbocationic polymerization; Isobutylene; Modeling; Kinetics; Mechanism; Run length

Characterization of poly(vinylidene fluoride–hexafluoropropylene) (PVdF–HFP) electrolytes complexed with different lithium salts by A. Manuel Stephan; S. Gopu Kumar; N.G. Renganathan; M. Anbu Kulandainathan (pp. 15-21).
Poly(vinylidene fluoride–hexafluoropropylene) (PVdF–HFP) gel electrolytes comprising a combination of plasticizers, ethylene carbonate (EC) and propylene carbonate (PC) and lithium salt LiX(X=BF4-,CF3SO3-,ClO4-) have been prepared using the solution casting technique in an argon atmosphere. The prepared electrolytes were subjected to ionic conductivity, compatibility with lithium metal anode and thermogravimetric (TG)/differential thermal analysis (DTA). The membranes, which possess lithium salt, LiBF4 exhibited maximum conductivity and on contrary it undergoes severe passivation with lithium metal. All these membranes are found to be stable thermally about 70°C.

Keywords: Polymer electrolyte; Ionic conductivity; Plasticizers; Thermal stability

Synthesis and curing studies of PPG based telechelic urethane methacrylic macromonomers by S.K. Asha; M. Thirumal; A. Kavitha; C.K.S. Pillai (pp. 23-33).
A New class of telechelic urethane methacrylic (TUMA) macromonomers were synthesized by a two-step condensation of 1, 6-hexamethylenediisocyanate (HMDI) with polypropylene glycol (PPG) of various molecular weights and capped with hydroxyl ethyl methacrylate (HEMA). A model compound based on diethylene glycol (DEG)—M-1 was synthesized as a low molecular weight analogue. Another model compound—M-2 was also synthesized by direct coupling of two equivalents of HEMA with HMDI. The structure of the telechelic urethanes were confirmed by1H,13C NMR and FTIR spectroscopy. Photopolymerization of these telechelic systems was investigated using 2,2-diethoxy acetophenone as the photoinitiator at 5 wt.%. Trihydroxymethylpropane trimethacrylate (30 parts), PPG diacrylates (25 parts), ethylhexyl acrylate (20 parts) were mixed with the various telechelic urethane methacrylates (25 parts) for curing studies. The kinetics of the curing was monitored by following the disappearance of the methacrylic double bonds at 1628 cm−1 using IR spectroscopy. TUMAPPG-425 had the fastest cure rate among the telechelic urethane methacrylates. This could be accounted for by hydrogen bonding pre-association in these systems. The thermal properties of the cured films were studied using TGA measurements. The cured films of the neat resin had a lower 50 wt.% loss temperature compared with that of the same resin in the formulation.

Keywords: Telechelic urethane methacrylates; UV-curing; Poly(propylene glycol)

Synthesis, characterization and photocrosslinking properties of polyacrylamides having bromo substituted pendant cinnamoyl moieties by P. Selvam; K. Victor Babu; S. Nanjundan (pp. 35-45).
New 3- and 4-bromocinnamoyl aniline were synthesized condensing 4-aminoacetophenone and the respective bromobenzaldehydes in the presence of sodium hydroxide. The monomers, 4-(3′-bromocinnamoyl) phenyl acrylamide (4,3′-BCPA) and 4-(4′-bromocinnamoyl) phenyl acrylamide (4,4′-BCPA) were prepared by reacting the respective chalcones and acryloyl chloride in the presence of triethylamine at 0–5°C. Homopolymers of 4,3′-BCPA and 4,4′-BCPA was carried out in methyl ethyl ketone using benzoyl peroxide (BPO) under nitrogen atmosphere at 70°C. The prepared polymers were characterized by UV, IR,1H-NMR and13C-NMR techniques. The molecular weights ( Mw and Mn) of the polymers were determined by gel permeation chromatography. The thermogravimetric analysis (TGA) of the polymers in nitrogen atmosphere reveals that they possess very good thermal stability required of a negative type photoresist. The glass transition temperature of poly(4,3′-BCPA) and poly (4,4′-BCPA) were found to be 55 and 64°C respectively. The solubility of the polymers was tested in various polar and non-polar solvents. Photocrosslinking nature of the polymer samples was carried out in the presence and absence of various triplet photosensitizers in solution phase using chloroform solvent under medium frequency UV light. For using the polymers as negative photoresist materials the rate of photocrosslinking of the polymers was measured under the influence of different solvents, concentrations and position of the substituent.

Keywords: Poly[4-(3′-bromocinnamoyl)phenyl acrylamide]; Poly[4-(4′-bromo cinnamoyl)phenyl acrylamide]; Photocrosslinking; Cinnamoyl group; Negative photoresist

Statistical copolymers of styrene and 2-vinylpyridine with trimethylsilyl methacrylate and trimethylsilyloxyethyl methacrylate by Garifalia Makrikosta; Dimitrios Georgas; Ekaterini Siakali-Kioulafa; Marinos Pitsikalis (pp. 47-54).
Statistical copolymers of styrene with trimethylsilyl methacrylate, STMS, and trimethylsilyloxyethyl methacrylate, STME, and of 2-vinylpyridine with trimethylsilyloxyethyl methacrylate, VTME were prepared by free radical copolymerization in benzene with 2,2′-azobisisobutyronitrile, AIBN. The reactivity ratios of the different monomers were estimated using the Finemann–Ross, the inverted Finemann–Ross, and the Kelen–Tüdos or the extended Kelen–Tüdos graphical methods. Structural parameters of the copolymers were obtained by calculating the diad sequence fractions, which were derived using the monomer reactivity ratios. The results were compared with those obtained from the copolymerization of styrene and 2-vinylpyridine with methacrylic acid and 2-hydroxyethyl methacrylate.

Keywords: Statistical copolymers; Styrene; 2-Vinylpyridine; Methacrylates; Reactivity ratios

The miscibility of poly(vinyl alcohol)/poly(N-vinylpyrrolidone) blends investigated in dilute solutions and solids by Katarzyna Lewandowska (pp. 55-64).
Poly(vinyl alcohol) (PVA) (polymer A) and poly(N-vinylpyrrolidone) (PVP) (polymer B) are known to form a thermodynamically miscible pair. In the present study the conclusion on miscibility of PVA/PVP solid blends, confirmed qualitatively (DMTA, FTIR) and quantitatively (DSC, χAB=−0.69 at 503 K) is compared with the miscibility investigations of PVA/PVP solution blends by the technique of dilute solution viscometry. The miscibility of the ternary (polymer A/ polymer B/ solvent) system is estimated on the basis of experimental and ideal values of the viscosity parameters k, b and [ η]. It is found that the conclusions on miscibility or nonmiscibility drawn from viscosity measurements in dilute solution blends depend: (i) on the applied extrapolation method used for the determination of the viscosity interaction parameters, (ii) on the assumed definition of the ideal values and (iii) on the thermodynamic quality of the solvent, which in the case of PVA depends on its degree of hydrolysis. Hence, viscometric investigations of dilute PVA/PVP solution blends have revealed that viscometry, widely used in the literature for estimation of polymer–polymer miscibility can not be recommended as a sole method to presume the miscibility of a polymer pair.

Keywords: Poly(vinyl alcohol); Poly(N-vinylpyrrolidone); Polymer blend; Miscibility

Soluble, thermally stable poly(ester amide)s derived from terephthalic acid bis(carboxydiphenyl methyl)ester and different diamines by Shahram Mehdipour-Ataei (pp. 65-71).
Terephthalic acid bis(carboxydiphenyl methyl)ester (TBE) as a new monomer for the preparation of polyamides was synthesized through the nucleophilic substitution reaction of benzilic acid with terephthaloyl chloride. This diester–diacid (TBE) was characterized using conventional spectroscopic methods. Polycondensation reactions of TBE with different aromatic and semi-aromatic diamines via Yamazaki method resulted different poly(ester amide)s. All the polymers were characterized and their physical and thermal properties were studied.

Keywords: Diamine; Polycondensation; Poly(ester amide)s; Thermal stability; Characterization

Preparation, morphology and properties of nano-sized Al2O3/polyimide hybrid films by Juntao Wu; Shiyong Yang; Shengqiang Gao; Aijun Hu; Jingang Liu; Lin Fan (pp. 73-81).
Nano-sized Al2O3/polyimide (PI) hybrid films based on 4,4′-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) were prepared by incorporation with different content of nano-sized Al2O3 via in situ polymerization. The TEM and SEM micrographs indicated that the Al2O3 particles were homogenously dispersed in the polyimide matrix by means of the ultrasonic treatment and the addition of coupling agent. The mechanical properties and thermal stability of the pure PI film can be improved by adequate addition of Al2O3. The PI hybrid film was strengthened and toughened simultaneously by the introduction of the well-dispersed Al2O3 particles. The PI hybrid films showed improved electrical aging performance as compared with pure PI film. Especially, the PI hybrid films with 10wt.% of Al2O3 content exhibited obviously enhanced electrical aging performance with the time to failure of 3.4 times longer than that of pure PI film. The improved electrical aging performance of the hybrid film was attributed to the nano-sized Al2O3 particles highly dispersed in the hybrid film, which confirmed by the investigation of the morphology and the surface composition of PI hybrid film before and after electrical aging.

Keywords: Polyimide; Hybrid film; Alumina; Morphology; Electrical aging

Substituent effect of bisindenyl zirconene catalyst on ethylene/1-hexene copolymerization and propylene polymerization by Wei Wang; Zhi-qiang Fan; Lin-xian Feng; Chong-he Li (pp. 83-89).
Nonbridged bis-substituted indenyl zirconene complexes were used as the catalysts for ethylene/1-hexene copolymerization and propylene polymerization. The complicated “comonomer effect? on the activity of ethylene/1-hexene copolymerization was observed. The effect also worked on the incorporation of comonomer. The number and the position of the substituents were important for the copolymerization behavior and the microstructure of the resultant copolymer as well as for propylene polymerization.

Keywords: Nonbridged metallocene; Ethylene copolymerization; Propylene polymerization; Comonomer effect

Novel thermally stable poly(sulfone ether ester imide)s by Shahram Mehdipour-Ataei (pp. 91-96).
A novel sulfone ether ester diamine was prepared by a three-step method. Reaction of 1,5-dihydroxy naphthalene with 4-nitrobenzoyl chloride afforded 5-hydroxy-1-naphthyl-4-nitrobenzoate. Reduction of nitro group by iron powder and HCl resulted in preparation of 5-hydroxyl-1-naphthyl-4-aminobenzoate. Reaction of this compound (two moles) with bis (4-chlorophenyl) sulfone led to preparation of a novel sulfone ether ester diamine. Three novel aromatic poly(sulfone ether ester imide)s were synthesized by polycondensation reactions of the prepared diamine with aromatic dianhydrides. Conventional methods were used to characterize the structure of the monomer and polymers. Physical properties of the polymers were also studied. The polyimides showed high thermal stability.

Keywords: Diamine; Polyimide; Thermal stability; Polycondensation; Poly(sulfone ether ester imide)

Studies on monitoring the composition of the copolymer by cyclic voltammetry and in situ spectroelectrochemical analysis by P. Santhosh; A. Gopalan; T. Vasudevan; T.-C. Wen (pp. 97-105).
Electrochemical copolymerization of diphenylamine (DPA) with ortho-toluidine (OT) was carried out in 4M sulphuric acid medium by cyclic voltammetry. Cyclic voltammograms (CVs) of the copolymer films were recorded to deduce the electrochemical characteristics. In situ UV–visible spectroelectrochemical studies on copolymerization were carried out using indium tin oxide (ITO) coated glass plate as working electrode for different feed ratios of DPA and OT. UV-visible spectral characteristics show clear dependencies on the molar feed composition of DPA or OT used in electropolymerization. Derivative cyclic voltabsorptogram (DCVA) was deduced at the wavelength corresponding to the absorption by the intermediate species and used to identify the intermediates generated during the electropolymerization. The molar composition of DPA and OT units in the copolymer for the copolymers synthesized with different molar feed ratios of DPA and OT was determined by UV–visible spectroscopy. Reactivity ratios of DPA and OT were deduced by using Fineman–Ross and Kelen–Tudos methods and the observed differences in the composition of DPA/OT in the copolymers were correlated with CV characteristics and results obtained from in situ spectroelectrochemical studies.

Keywords: Electrocopolymerization; Cyclic voltammetry; In situ spectroelectro studies; UV–visible spectroscopy; Copolymer composition; Reactivity ratios

Synthesis, characterization and degradation of a novel class of fluorescent poly[1,3-bis( p-carboxyphenoxy) propane: p-(carboxyethylformamido)benzoic anhydride] (P(CPP:CEFB)) by D. Chen; H.L. Jiang; K.J. Zhu (pp. 107-113).
One class of fluorescent copolyanhydrides were synthesized by melt copolycondensation of the fluorophoric diacid, p-(carboxyethylformamido)benzoic acid (CEFB), with 1,3-bis( p-carboxyphenoxy) propane (CPP).1H NMR spectra of the copolymers confirm their chemical structures. All the copolymers can give off fluorescence with the excitation of both UV (356nm) and visible light (470nm). The fluorescence intensity increases with an increase in CEFB fraction. The degradation rate of the copolyanhydrides can be modulated by the polymer components, increasing with a decrease in CPP content. In addition, CEFB segments in the copolymers degraded rapider than CPP segments, resulting in an increase in CPP fraction in the degraded copolyanhydrides. Morphology change of the copolyanhydrides during degradation was also examined by SEM. It was found that the outer layers of the degraded samples erode faster than the inner layers. Fluorescence intensity of the degraded copolyanhydrides diminished with time.

Keywords: Biodegradable polymers; Copolymers; Fluorescence; Degradation

Polymerization of vinyl chloride catalyzed by a titanium complex with an anionic oxygen tripod ligand by Jun-Ting Xu; Qi Wang; Fei Wu; Zhi-Qiang Fan (pp. 115-120).
Poly(vinyl chloride) (PVC) was prepared using a titanium complex with an anionic oxygen tripod ligand [CpCo{P(O)(OEt)2}3] (LOEt-) as catalyst and methyl aluminoxane (MAO) as cocatalyst. The polymerization behavior was compared with that of pentamethyl cyclopentadienyl titanium trichloride (Me5CpTiCl3). It is observed that LOEtTiCl3 can polymerize vinyl chloride with activity comparable to that of Me5CpTiCl3. The PVC samples prepared with LOEtTiCl3/MAO exhibit bimodal molecular weight distribution and the fraction of high molecular weight peak decreases with polymerization temperature. The microstructure and thermal decomposition of the PVC obtained were studied. Five types of structural defect were detected by1H-NMR. Only saturated structural defects are found at low polymerization temperature, but at high polymerization temperature unsaturated structural defects, possibly resulting from dehydrochlorination of the saturated structural defects, appear as well. No head-to-head structural defect is observed.13C-NMR shows that the PVC prepared by LOEtTiCl3 has an atactic stereostructure. Compared with the PVC from radical polymerization and anionic polymerization, the PVC samples prepared with LOEtTiCl3 show improved thermal stability.

Keywords: Poly(vinyl chloride); Ti complex; Structural defects; Thermal stability

Synthesis, characterization and H2O2-sensing properties of pyrimidine-based hyperbranched polyimides by Süleyman Köytepe; Aziz Paşahan; Ergun Ekinci; Turgay Seçkin (pp. 121-127).
A series of hyperbranched polyimides having pyrimidine core in the backbone was prepared by solution polycondensation of pyromellitic dianhydride (A2 type) and 2,4,6-triaminopyrimidine (B3 type). The resulting polyimides were characterized by IR, GPC, DTA, DSC, TGA, density and viscosity measurement. The results showed that polyimides were obtained in 82–86% yield, had inherent viscosities of 1.58–1.87dL/g and highly thermal stability. From the solubility tests, it was found that all the polyimides were soluble in NMP, DMAc and DMSO at room temperature. In addition, because of their interesting film properties, attempts were made to prepare H2O2-sensing polyimide material. For this reason, selectivity of film-coated electrodes obtained from the chemically prepared hyperbranched polyimides toward electroactive (ascorbic acid, oxalic acid and hydrogen peroxide) and non-electroactive (lactose, sucrose and urea) species was examined by means of CV, DPV and TB techniques. From the electrochemical data obtained, it has been demonstrated that polyimide (HPI-2) film responded to only hydrogen peroxide among the species examined. In other words, it has been claimed that the mentioned polyimide-coated electrode can be used as H2O2-selective membrane in the presence of the electroactive and non-electroactive interferents.

Keywords: Polyimide; Film; Selective membrane

Crystalline properties and morphological changes in plastically deformed isotatic polypropylene evaluated by X-ray diffraction and transmission electron microscopy by G. Machado; E.L.G. Denardin; E.J. Kinast; M.C. Gonalves; M.A. de Luca; S.R. Teixeira; D. Samios (pp. 129-138).
The isotatic polypropylene (i-PP) plastically deformed by uniaxial plane strain compression was investigated using X-ray diffraction and transmission electron microscopy. The apparent crystallinity was evaluated by means of X-ray diffraction with a profile matching using a FULLPROF code. Two crystalline phases, α and β, were identified in the non-deformed polymer as well as with an amorphous halo. The deformation with 3, 10 and 100MPa, induces an increase of the amorphous halo. The microstructural orientation of the i-PP, before and after deformation was evaluated using the “Quantikov? image analysis of transmission electron microscopy (TEM) data. The non-deformed material presents spherulitic structure, without any preferential orientation. The high resolution, in the nanometer scale, shows two preferential orientation axes. The deformation at 3, 10 and 100MPa, affects the spherulitic, as well as, the lamellae structure, introducing fiber orientation, a break up of the lamellae in to small blocks and consequently amorphization of the system.

Keywords: Polypropylene; X-ray diffraction; Transmission electronic microscopy

Modeling of the θ(lower critical solution temperature) in polymer solutions using molecular connectivity indices by Hongwei Liu; Chongli Zhong (pp. 139-147).
In this work, correlations for the estimation of the θ(lower critical solution temperature, LCST) for Polystyrene, Polyethylene, Polypropylene, Polybutene-1, Polypentene-1, Poly(4-methylpentene-1), Polydimethylsiloxane and Polyisobutylene solutions were proposed based on the molecular connectivity index. The correlations give satisfactory estimation of the θ(LCST), with the absolute error smaller than 20 K for most systems studied. Since the new correlations require only molecular connectivity indices of the solvent in the calculations, and the molecular connectivity indices can be calculated easily once the molecular structure of the substance concerned is known, they have better predictive capability and are easier to apply comparing with the existing methods and models.

Keywords: Modeling; Theta; Lower critical solution temperature; Polymer solution; Molecular connectivity index

Studies of silicon-containing maleimide polymers: 1. Synthesis and characteristics of model compounds by Wei-Jye Shu; Jiau-Ching Ho; Li-Hsiang Perng (pp. 149-156).
A series of the ( N-maleimido phenoxy)silane monomers were synthesized by a two-step reaction for using as the application of flame retardant, functional modifier, or a photoresist material in deep-UV region. All of the monomers with maleimide ring were polymerized by radical polymerization in toluene solution using 2,2′-azobisisobutyronitrile (AIBN) as initiator so as to prepare homopolymers. The structures of the maleimide monomers were identified by1H,13C,29Si NMR and element analysis. The chemical structures of polymers were identified by Fourier transform infrared reflection (FT-IR) spectroscopy. The molecular weight distributions of polymers were measured by gel permeation chromatography (GPC) equipment. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to analyze the thermal properties of the polymers. The degree of polymerization in silicon-containing maleimide polymers should be affected by side chains. The introduction of alkylsilane into a side chain of maleimide polymer may reduce the glass transition temperature ( Tg) and thermal stability, but increase char yield of solid residue as an excellent flame retardant.

Keywords: Silicon-containing maleimide polymers; Alkylsilane; Flame retardant; Thermal stability

Thermal and photochemical curing of isocyanate and acrylate functionalized oligomers by K. Studer; C. Decker; E. Beck; R. Schwalm (pp. 157-167).
Dual-cure formulations have been developed in order to broaden the range of applications of UV-radiation curing and achieve a sufficient cure of the non-illuminated areas of protective coatings, like the shadow areas of three-dimensional substrates or the deep-lying layers of thick pigmented coatings. In complement to the conventional acrylic photopolymerization, such systems involve a polyaddition reaction between isocyanate and hydroxyl functions upon heating, thus imparting satisfying mechanical properties to the coatings, even in the non-irradiated areas. For a quantitative study of the two curing reactions, infrared spectroscopy was chosen because it allows one to monitor accurately the chemical modifications induced in thin films by heat or light. This technique proved particularly useful to follow the polyaddition reaction through the decay of the characteristic IR band of the isocyanate group at 2271cm−1. Several factors were shown to affect the reaction rate, in particular the chemical structure of the various functionalized compounds, the moisture content in the atmosphere, the curing temperature and the presence of amino catalysts. The viscoelastic properties of the resulting material have been evaluated by dynamic mechanical analysis and shown to be highly dependent on the curing conditions and the type of polymer network formed. For coatings which remain too soft in the dark areas, a thermal initiator was added to promote some further polymerization of the acrylate monomers.

Keywords: Dual-cure; UV-curing; Acrylate coatings; Isocyanates; Shadow areas; Pigmented coatings

Influence of temperature and nature of photoinitiator on the formation kinetics of an interpenetrating network photocured from an epoxide/methacrylate system by L. Lecamp; C. Pavillon; P. Lebaudy; C. Bunel (pp. 169-176).
This paper deals with the synthesis of an interpenetrating network made of dimethacrylate and dicycloepoxide oligomers by photopolymerization. More particularly, the influence of several parameters (among which the photoinitiator nature and the reaction temperature) on the polymerization kinetics of each oligomer was studied. Two complementary analysis techniques were then used : the photocalorimetry and the RTIR spectroscopy. The study proceeded in several steps. Firstly, photopolymerization of each monomer was studied. Then, the same study was carried out on mixture of both monomers under conditions in such way than only one network is formed. It was shown that the second compound played the role of plasticizer on the network formed by the first monomer. Finally, the dimethacrylate/dicycloepoxide mixture was studied in the presence of both radical and cationic photoinitiators to synthesize an interpenetrating network (IPN). At 30C, ultimate products show a very incomplete epoxide conversion whereas the yield in methacrylic double bonds reaches 70%. On the other hand, epoxy functions react a little more than methacrylic double bonds at 90C. It was also shown that the presence of a radical photoinitiator is not necessary, and even slightly unfavourable, since the cationic photoinitiator is able to initiate both radical and cationic polymerization mechanisms.

Keywords: UV-curing; Methacrylate; Epoxide; Interpenetrating network

Redox polymerization of methyl methacrylate with allyl alcohol 1,2-butoxylate- block-ethoxylate initiated by Ce(IV)/HNO3 redox system by Cigdem Yagci; Ufuk Yildiz (pp. 177-184).
Redox initiated free-radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2-butoxylate- block-ethoxylate (AABE) was carried out using cerium(IV) ammonium nitrate/nitric acid (HNO3) redox system to yield AABE- b-PMMA copolymers. The effects of MMA, AABE, Ce(IV) and HNO3 concentrations on the polymerization rate and polymer yield were investigated. The effect of temperature on the rate of polymerization and polymer yield was also investigated in the temperature range of 25–70°C. Copolymers were characterized using GPC, FT-IR,1H NMR and viscometry methods.

Keywords: Redox polymerization; Cerium(IV) ammonium nitrate; Free-radical polymerization

Fluorescence observations on complex formation between linear and hyperbranched polyelectrolytes in dilute aqueous solutions by Chaoyang Wang; Biye Ren; Zhen Tong; Fang Zeng; Xinxing Liu; Shuizhu Wu; Ping Liu (pp. 185-191).
The complexation between poly(ethylene imine) (PEI) and poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) or AMPS copolymers was investigated with the relative excimer emission intensity IE/ IM of a cationic probe 1-pyrenemethylamine hydrochloride (PyMeA·HCl), fluorescence nonradiative energy transfer (NRET) IPy/ INp of naphthalene to pyrene labels, the fluorescence anisotropy r and IE/ IM of pyrene labels. PEI was a hyperbranched weak polycation in acid solution, which formed complex with anionic polyelectrolytes due to the electrostatic attraction. The IE/ IM of PyMeA·HCl probe decreased to zero, the intra-, intermolecular NRET IPy/ INp and IE/ IM of pyrene labels on the AMPS copolymers reached their maxima when χ was increased from 0 to 2.4, which was defined as the mole ratio of the amino group in PEI to the AMPS group in the polyanion. These facts indicated the formation of nonstoichiometric complex of the oppositely charged polyelectrolytes when χ=2.4 at the concentration much lower than their overlap concentrations. The intermolecular aggregate appeared as indicated by an increase in the intermolecular IPy/ INp and r with χ up to 2.4 due to neutralizing and hydrophobizing the polyelectrolytes and the bridging effect of the PEI chain bound on different polyanion chains. At high pH, PEI became a neutral polymer and did not bind with the AMPS anion to form the complex as illustrated by the constant value of r for the pyrene labels attached to the AMPS polyanion as that without addition of PEI. The amino group in PEI quenched pyrene and naphthalene emission, resulting a decrease in both INp and IPy.

Keywords: Polyelectrolyte complex; PAMPS; PEI; Fluorescence label; NRET; Excimer emission

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