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Polymerization Rate (polymerization + rate)
Selected AbstractsRAFT Miniemulsion Polymerization Kinetics, 1 , Polymerization RateMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2009Hidetaka Tobita Abstract The polymerization kinetics of a RAFT-mediated radical polymerization inside submicron particles (30,<,Dp,<,300 nm) is considered. When the time fraction of active radical period, ,A, is larger than ca. 1%, the polymerization rate increases with reducing particle size, as for the cases of conventional emulsion polymerization. The rate retardation by the addition of RAFT agent occurs with or without intermediate termination in zero-one systems. For the particles with Dp,<,100 nm, the statistical variation of monomer concentration among particles may not be neglected. It was found that this monomer-concentration-variation (MCV) effect may slow down the polymerization rate. An analytical expression describing the MCV effect is proposed, which is valid for both RAFT and conventional miniemulsion polymerizations. [source] Influence of Structure on Polymerization Rates and Ca-Binding of Phosphorus-Containing 1,6-DienesMACROMOLECULAR REACTION ENGINEERING, Issue 5 2007Aylin Ziylan Albayrak Abstract Photo- and thermal-polymerizations of 4-diethoxyphosphoryl-2,4,6-tris(ethoxycarbonyl)-1,6-heptadiene, 4,4-bis(diethoxyphosphoryl)-2,6-bis(t -butoxycarbonyl)-1,6-heptadiene and 4-diethoxyphosphoryl-4-ethoxycarbonyl-2,6-bis(t -butoxycarbonyl)-1,6-heptadiene monomers and their phosphonic and carboxylic acid derivatives were investigated to understand the effect of the cyclic monomer structure on their polymerization reactivity. A strong effect of the substituents at positions 2, 4 and 6 of the monomers on polymerization rate was observed. The polymerizability of the monomers was successfully correlated with the 13C NMR chemical shifts of the vinyl carbons. Conversion values were consistent with the Tg being a measure of the flexibility of a monomer. The monomers containing phosphonic acid groups were soluble in water and ethanol. The acidic nature of the aqueous solutions of these monomers is expected to give them etching properties, important for dental applications. The interaction of the acid monomers with hydroxyapatite was investigated using 13C NMR technique. [source] Hydrogen response in liquid propylene polymerization: Towards a generalized modelAICHE JOURNAL, Issue 5 2006M. Al-haj Ali Abstract Liquid propylene batch experiments in the absence of a gas phase have been carried out using a highly-active MgCl2/TiCl4/phthalate/silane/AlR3 catalyst at varying temperatures (60-80°C) and molar hydrogen-monomer ratios of 0-10 mmol/mol. With increasing hydrogen concentration the polymerization rate increases rapidly, reaching a constant value at concentrations above 1.4 mmol/mol; pseudo-first-order catalyst deactivation constant increases; molecular weight decreases; polydispersity decreases slightly; but average molecular weight and polydispersity increase with increasing temperature. Polymerization rate, deactivation constant, and average molecular weight can be modeled based on a consistent dormant site mechanism assuming an (averaged) quasi-single-site model. © 2006 American Institute of Chemical Engineers AIChE J,2006 [source] Modeling of the Nitroxide-Mediated Radical Copolymerization of Styrene and DivinylbenzeneMACROMOLECULAR REACTION ENGINEERING, Issue 5-6 2009Julio C. Hernández-Ortiz Abstract A mathematical model for the copolymerization kinetics with crosslinking of vinyl/divinyl monomers in the presence of nitroxide controllers has been developed and validated using experimental data of TEMPO-mediated copolymerization of styrene (STY) and divinylbenzene (DVB). Polymerization rate, molecular weight development, gelation point, evolution of sol and gel weight fractions, crosslink density, and copolymer composition, as well as concentrations of the species participating in the reaction mechanism can be calculated with the model. Diffusion-controlled effects were assessed and found unimportant. The presence of nitroxide controllers seems to favor the production of more homogeneous polymer networks, but this effect decreases as the initial fraction of crosslinker is increased. [source] Kinetics and Modeling of Vinyl Acetate Graft Polymerization from Poly(ethylene glycol)MACROMOLECULAR REACTION ENGINEERING, Issue 4 2008Xiaoxiang Zhu Abstract A kinetic model for the graft polymerization of VAc from PEG was developed using the method of moments. Experiments were carried out to verify the model. The effect of various parameters, such as initiator concentration, temperature, and PEG molecular weight on the polymerization kinetics was examined. Polymerization rate, grafting efficiency, graft copolymer molecular weight, and PEG grafted ratio were measured. The model was in good agreement with the experimental data. No gel effect was observed at the studied PEG/VAc weight ratio of 1:1. The chain transfer constant to PEG was correlated to be . The model was also applied in a semi-batch reaction and compared with the experimental results. [source] Effect of initiator type and concentration on polymerization rate and molecular weight in the bimolecular nitroxide-mediated radical polymerization of styreneADVANCES IN POLYMER TECHNOLOGY, Issue 1 2010Telma Regina Nogueira Abstract To increase the polymerization rate in the bimolecular nitroxide-mediated radical polymerization (NMRP) of styrene, without using expensive non-commercial reagents, an experimental study using 2,2,6,6-tetramethyl-1-piperidinoxyl as a controller and tert-butylperoxy 2-ethylhexyl carbonate (TBEC) as the initiator was carried out. The basis for comparison was the bimolecular NMRP of styrene with dibenzoyl peroxide as initiator. It was found that faster polymerization rates and still relatively low polydispersities were possible using TBEC. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:11,19, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20170 [source] Epoxy,siloxane hybrid coatings by a dual-curing processADVANCES IN POLYMER TECHNOLOGY, Issue 2 2009Giulio Malucelli Abstract Coatings based on a hybrid organic,inorganic epoxy system were prepared by a dual-curing mechanism, via cationic photopolymerization in the first step at room temperature and a subsequent hydrolysis/condensation reaction of a trialkoxy-silane compound (sol,gel process) at high temperature. To this end, a high Tg epoxy resin (3,4-epoxycyclohexylmethyl-3,-cyclohexenyl-methyl adipate, UVR 6128) was added in increasing amounts to a precursor for the inorganic-like phase (3,4-epoxycyclohexylethyltrimethoxysilane, EETMOS). The mixture contained triphenylsulfoniumhexafluoroantimonate as a cationic photoinitiator. By this method, the strongly acid environment generated by the photolysis of the triarylsolfunium salt in the first step induces the hydrolysis of EETMOS alkoxy-silane groups. The films produced in the first step of the process were thermal treated to promote the condensation reactions of the siloxane moieties. The kinetics of the reactions of photopolymerization and condensation was investigated. It was found that the presence of EETMOS increases both the polymerization rate and the final consumption of epoxy groups. Thermogravimetric analyses performed in air have revealed an increased stability of the hybrid coatings with respect to the films produced from formulations without EETMOS. A significant increase in surface hardness was also observed for the hybrid coatings. The thermo-mechanical properties were found to be strongly affected by the temperature used in the thermally induced reactions in the second step. The hybrid coatings on a low-density polyethylene substrate were found to decrease the diffusivity of oxygen and to increase the oxygen solubility within the coating. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:77,85, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20149 [source] Hybrid titanium catalyst supported on core-shell silica/poly(styrene- co -acrylic acid) carrierJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Lijun Du Abstract Hybrid titanium catalysts supported on silica/poly(styrene- co -acrylic acid) (SiO2/PSA) core-shell carrier were prepared and studied. The resulting catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, laser scattering particle analyzer and scanning electronic microscope (SEM). The hybrid catalyst (TiCl3/MgCl2/THF/SiO2·TiCl4/MgCl2/PSA) showed core-shell structure and the thickness of the PSA layer in the two different hybrid catalysts was 2.0 ,m and 5.0 ,m, respectively. The activities of the hybrid catalysts were comparable to the conventional titanium-based Ziegler-Natta catalyst (TiCl3/MgCl2/THF/SiO2). The hybrid catalysts showed lower initial polymerization rate and longer polymerization life time compared with TiCl3/MgCl2/THF/SiO2. The activities of the hybrid catalysts were enhanced firstly and then decreased with increasing P/P. Higher molecular weight and broader molecular weight distribution (MWD) of polyethylene produced by the core-shell hybrid catalysts were obtained. Particularly, the hybrid catalyst with a PSA layer of 5.0 ,m obtained the longest polymerization life time with the highest activity (2071 kg PE mol,1 Ti h,1) and the resulting polyethylene had the broadest MWD (polydispersity index = 11.5) under our experimental conditions. The morphology of the polyethylene particles produced by the hybrid catalysts was spherical, but with irregular subparticles due to the influence of PSA layer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Analyzing the real advantages of bifunctional initiator over monofunctional initiator in free radical polymerizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Paula F. de M. P. B. Machado Abstract Monofunctional initiators are extensively used in free radical polymerization. To enhance productivity, a higher temperature is usually used; however, this leads to lower molecular weights. Bifunctional initiators can increase the polymerization rate without decreasing the average molecular weight and this can be desirable. A bifunctional initiator is an important issue to be investigated, and it is of great interest to industries. The objective of this work is to study polymerization reactions with mono- and bi-functional initiators through comprehensive mathematical models. Polystyrene is considered as case study. This work collects and presents some experimental data available in literature for polymerization using two different types of bifunctional initiators. Model prediction showed good agreement with experimental data. It was observed that the initial initiator concentration has a huge impact on the efficiency of initiators with functionality bigger than one and high concentrations of bifunctional initiator make the system behave as if it were a system operating with monofunctional initiator. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Kinetics of methyl methacrylate grafting polymerization onto flaky aluminum powderJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Hui Liu Abstract With ammonium persulfate (APS) as the initiator, the kinetics of methyl methacrylate (MMA) grafting polymerization onto flaky aluminum powder (Al) was studied. It was found that the experimental apparent grafting polymerization rate, Rg = KC × C × C, was basically consistent with the theoretical result based on the theory of stable polymerization and equivalent activity, Rg = KC × C × CMMA. The activation energy of grafting, homogenous, and total polymerization rate was calculated as 65.1, 35.4, and 37.5 kJ mol,1, respectively. It could be validated that the relationship among these activation energies accorded with the theoretical result of parallel reactions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Emulsion polymerization of styrene with amphiphilic random copolymer as surfactant: Predominant droplet nucleationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Li Liu Abstract Amphiphilic random copolymer consisting of monomeric units of poly (butyl acrylate) and poly (maleic acid salt) was synthesized and characterized. The emulsion polymerization kinetics of styrene stabilized by this copolymer was investigated. The influencing factors, including polymeric surfactant concentration, initiator concentration and polymerization temperature, were systematically studied. The kinetic data show that the polymerization rate (RP) increased with the increase of the polymeric surfactant concentration ([S]) and polymerization temperature (T). At the higher [S], droplets nucleation and micelle nucleation coexisted in the polymerization system; at the lower [S], only the droplets nucleation process existed. The polymerization did not follow Smith-Ewart Case II kinetics. Dynamic light scatter and transmission electron microscope were utilized to measure the sizes and shapes of the particles, respectively. It would be speculated that a kind of large heterogeneous particles with multiple-active-sites was formed in the polymerization system. The increasing of RP with increasing initiator concentration ([KPS]) was rapid at a medium [KPS], but the slowly increasing was observed at a lower or higher [KPS]. It was attributed to the barrier effect of the polymeric surfactant around the monomer droplets. The polymerization activation energy was 60.29 kJ/mol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Effect of the carboxylic acid monomer type on the emulsifier-free emulsion copolymerization of styrene and butadieneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2007Mahdi Abdollahi Abstract Carboxylated styrene,butadiene rubber latexes were prepared through the emulsifier-free emulsion copolymerization of styrene and butadiene with various carboxylic acid monomers. The effects of various carboxylic acid monomers on the particle formation process were investigated. The type of carboxylic acid monomer strongly affected the particle nucleation. The number of particles and thus the polymerization rate increased with the increasing hydrophobicity of the carboxylic acid monomers. There was a significant difference in the polymerization rate per particle. The results showed that particle nucleation and growth were dependent on the hydrophilic nature of the carboxylic acid monomers. The average particle diameter of the carboxylated styrene,butadiene rubber latexes in the dry state was obtained through some calculations using direct measurements of the average particle diameter in the monomer-swollen state by a dynamic light scattering technique. Several parameters, such as the polymerization rate, number of latex particles per unit of volume of the aqueous phase, and polymerization rate per particle, were calculated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Miniemulsion polymerization of a fluorinated acrylate copolymer: Kinetic studies and nanolatex morphology characterizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Qinghua Zhang Abstract A stable fluoroacrylate copolymer emulsion was successfully prepared by miniemulsion polymerization with fluoroacrylate, lauryl methylacrylate, and methyl methacrylate as monomers. Extremely hydrophobic fluoroacrylate, instead of conventional cosurfactants, was used as a reactive cosurfactant to stabilize the miniemulsions. The results indicated that fluoroacrylate retarded Ostwald ripening and allowed the production of stable miniemulsions. The chemical compositions of the copolymer were studied with Fourier transform infrared and 1H-NMR. The average composition of the copolymers prepared with miniemulsions was in good agreement with the feed ratio according to 1H-NMR from the integration ratios corresponding to typical protons of the individual monomers. The particle size distribution and morphology of the latex particles were determined with laser particle analysis and transmission electron microscopy. The particle size of the latex underwent no change in the process of miniemulsion polymerization, but the particle size distributions were broader than those of conventional emulsion polymerization. The effects of various reaction parameters, including the temperature and concentrations of the emulsifier and initiator, on the miniemulsion polymerization were also investigated, and the polymerization rate and conversion increased with increasing concentrations of nonylphenol polyethoxylate (with an average of 40 ethylene oxide units per molecule), cetyltrimethylammonium, and 2,2,-azobisisobutyronitrile. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 641,647, 2007 [source] Kinetics of graft copolymerization of poly(hexanedioic acid ethylene glycol) and methyl acrylate initiated by potassium diperiodatocuprate(III)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Libin Bai Abstract A redox system, potassium diperiodatocuprate(III) [DPC]/poly(hexanedioic acid ethylene glycol) (PEA) system, was employed to initiate graft copolymers of methyl acrylate (MA) and PEA in alkaline medium. The results indicate that the equation of the polymerization rate (Rp) is as follows: Rp = k [MA]1.62[Cu(III)]0.69, and that the overall activation energy of graft polymerization is 42.5 kJ/mol. The total conversion at different conditions (concentration of reactants, temperature, concentration of the DPC, and reaction time) was also investigated. The infrared spectra proved that the graft copolymers were synthesized successfully. Some basic properties of the graft copolymer were studied by instrumental analyses, including thermogravimetry and scanning electron microscope. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2376,2381, 2007 [source] Hydrogen response in liquid propylene polymerization: Towards a generalized modelAICHE JOURNAL, Issue 5 2006M. Al-haj Ali Abstract Liquid propylene batch experiments in the absence of a gas phase have been carried out using a highly-active MgCl2/TiCl4/phthalate/silane/AlR3 catalyst at varying temperatures (60-80°C) and molar hydrogen-monomer ratios of 0-10 mmol/mol. With increasing hydrogen concentration the polymerization rate increases rapidly, reaching a constant value at concentrations above 1.4 mmol/mol; pseudo-first-order catalyst deactivation constant increases; molecular weight decreases; polydispersity decreases slightly; but average molecular weight and polydispersity increase with increasing temperature. Polymerization rate, deactivation constant, and average molecular weight can be modeled based on a consistent dormant site mechanism assuming an (averaged) quasi-single-site model. © 2006 American Institute of Chemical Engineers AIChE J,2006 [source] Surfactant assisted polymerization of tetrafluoroethylene in supercritical carbon dioxide with a pilot scale batch reactorJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008Alberto Giaconia Abstract Chain-free radical polymerization of tetrafluoroethylene (TFE) was carried out in supercritical carbon dioxide (scCO2), at 50 °C and 121,133 bar, with tertiary -amyl-per-pivalate as a free radical initiator, using a 5-L pilot scale batch reactor. Experiments were carried out both in the absence and in the presence of perfluoropolyether (PFPE) carboxylate surfactants. Stabilizers were employed under the free acid form and as sodium and calcium salts. An expanded fibrillated poly(TFE) was obtained in all experiments. In the case of surfactant-free polymerizations, the product was mainly constituted by irregular shape macroparticles having size in the range 200,500 ,m. Quite interestingly, when the free acid surfactant was used, a clear acceleration of the polymerization rate was observed and smaller polymer particles with more regular quasi-spherical morphology were obtained. Melt fusion crystallinity of as-polymerized poly(TFE) seemed not substantially affected by the presence of the stabilizers and was rather high (80,86%) suggesting that polymerization mainly occurs at polymer particle surface. All these elements suggest that FLUOROLINK® 7004H PFPE carboxylic acid decreases coagulation of primary polymer particles leading to an increase in polymer surface area. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 257,266, 2008 [source] Cagelike polymer microspheres with hollow core/porous shell structuresJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2007Xiaodong He Abstract Submicron-scaled cagelike polymer microspheres with hollow core/porous shell were synthesized by self-assembling of sulfonated polystyrene (PS) latex particles at monomer droplets interface. The swelling of the PS latex particles by the oil phase provided a driving force to develop the hollow core. The latex particles also served as porogen that would disengage automatically during polymerization. Influential factors that control the morphology of the microspheres, including the reserving time of emulsions, polymerization rate, and the Hildebrand solubility parameter and polarity of the oil phase, were studied. A variety of monomers were polymerized into microspheres with hollow core/porous shell structure and microspheres with different diameters and pore sizes were obtained. The polymer microspheres were characterized by scanning electron microscopy, transmission electron microscopy, optical microscopy, and Fourier transform infrared spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 933,941, 2007 [source] Synthesis and properties of the polythiourethanes obtained by the cationic ring-opening polymerization of cyclic thiourethanesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2006Daisuke Nagai Abstract The cationic ring-opening polymerization of a five-membered thiourethane [3-benzyl-1,3-oxazolidine-2-thione (BOT)] with boron trifluoride etherate afforded the corresponding polythiourethane with a narrow molecular weight distribution in an excellent yield. The molecular weight of the polymers could be controlled by the feed ratio of the monomer to the initiator. A kinetic study of the polymerization revealed that the polymerization rate of BOT (1.3 × 10,2 L mol,1 min,1) was two times larger than that of the six-membered thiourethane [3-benzyltetrahydro-1,3-oxazolidine-2-thione (BTOT); 6.8 × 10,3 L mol,1 min,1], and the monomer conversion obeyed the first-order kinetic equation. These observations, along with the successful results in the two-stage polymerization, supported the idea that this polymerization proceeded in a controlled manner. Block copolymerizations of BOT with BTOT were also carried out to afford the corresponding di- and triblock copolymers with narrow molecular weight distributions. The order of the 5% weight loss temperatures was as follows: poly(3-benzyltetrahydro-1,3-oxazolidine-2-thione) [poly(BTOT)] > poly(BTOT54 - b -BOT46) > poly(3-benzyl-1,3-oxazolidine-2-thione) [poly(BOT)]. This indicated that an increase in the BTOT unit content raised the decomposition temperature. The order of the refractive indices was poly(BOT) > poly(BTOT54 - b -BOT46) > poly(BTOT54 - b -BOT46 - b -BTOT50) > poly(BTOT); this was in accord with the order of the sulfur content in the polymer chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4795,4803, 2006 [source] Homopolymerization of cyclic esters initiated by lanthanide isopropoxides supported by 2,2,-ethylene-bis(4,6-di- tert -butylphenolate) ligandsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2006Xiaoping Xu Abstract Lanthanide isopropoxides supported by carbon-bridged bisphenolate ligands of 2,2,-ethylene-bis(4,6-di- tert -butylphenoxo) {[(EDBP)Ln(,-OPri)(THF)2]2, where Ln is Nd (1), Sm (2), or Yb (3) and THF is tetrahydrofuran} were synthesized by protic exchange reactions in high yields with Cp3Ln compounds as raw materials, and complex 1 was structurally characterized. Complexes 1,3 were shown to be efficient initiators for the ring-opening polymerization of ,-caprolactone (,-CL) and 2,2-dimethyltrimethylene carbonate (DTC). Complexes 1,3 could initiate the controlled polymerization of ,-CL, and the polymerization rate was first-order with respect to the monomer. The influence of the reaction conditions on the monomer conversion, molecular weight, and molecular weight distribution of the resultant polymers was investigated. End-group analyses of the oligomers of ,-CL and DTC showed that the polymerization underwent a coordination,insertion mechanism. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4409,4419, 2006 [source] Nitroxide-mediated homo- and block copolymerization of styrene and multifunctional acryl- and methacryl derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005Meizhen Yin Abstract The ability of different alkoxyamines (I1, I2, I3, I4, and I5) to initiate controlled radical polymerization of styrene was evaluated. Among them, 2-hydroxymethyl-2-[(2-methyl-1-phenyl-propyl)-(1-phenyl-ethoxy)-amino]-propane-1,3-diol (I5) gave the highest polymerization rate of styrene, and the best control over the molecular weight and the molecular weight distribution of polystyrene. Kinetic studies confirmed that with initiator I5 the polymerization of styrene proceeded in a controlled way. The controlled radical homopolymerization of multifunctional acryl- and methacryl derivatives using initiator I5 could not be realized as demonstrated by the high polydispersities (PD) obtained. However, it was possible to polymerize multifunctional acryl- and methacryl derivatives using a polystyrene macroinitiator (Pst) and, thus, novel amphiphilic block copolymers with a narrow molecular weight distribution were obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1873,1882, 2005 [source] Semibatch emulsion polymerization of methyl methacrylate using different polyurethane particlesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2005ebenik Abstract Aqueous acrylic-polyurethane (AC,PU) hybrid emulsions were prepared by semibatch emulsion polymerization of methyl methacrylate (MMA) in the presence of four polyurethane (PU) dispersions. The PU dispersions were synthesized with isophorone diisocyanate (IPDI), 1000 and 2000 molecular weight (MW) poly(neopentyl) adipate, 1000 MW polytetramethyleneetherglycol, butanediol (BD), and dimethylol propionic acid (DMPA). MMA was added in the monomer emulsion feed. We studied the effect of the use of different PU seed particles on the rate of polymerization, the particle size and distribution, the number of particles, and the average number of radicals per particle. The PU rigidity was controlled by varying the polyol chemical structure, the polyol MW (Mn), and by adding BD. The monomer feed rate was varied to study its influence on the process. It was observed that the PU particles that had been prepared with a higher MW polyol swelled better with MMA before the monomer-starved conditions occurred. There seemed to be no significant discrepancies between the series with different PU seeds in the monomer-starved conditions. The overall conversion depended on the monomer addition rate, and the polymerization rate acquired a constant value that was comparable to the value of the monomer addition rate. The instantaneous conversion increased slightly. The average particle size increased, and the total particle number in the reactor was constant and similar to the number of PU particles in the initial charge. The average number of radicals per particle increased. The differences between the system with a constant particle number and average number of radicals per particle and the system with a fixed radical concentration are discussed. The semibatch emulsion polymerization of MMA in the presence of PU particles studied was better compared to the system with a fixed radical concentration. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 844,858, 2005 [source] Dithiocarbamate mediated controlled/living free radical polymerization of methyl acrylate under 60Co ,-ray irradiation: Conjugation effect of N -groupJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2004Daoben Hua Abstract The free radical polymerizations of methyl acrylate have been studied under ,-ray irradiation in the presence of the dithiocarbamates with different N -groups. The results indicate that the conjugation structure of the N -group of dithiocarbamate plays an important role in living free radical polymerization. The polymerizations reveal good living characteristics in the presence of dithiocarbamates (benzyl 1H-imidazole-1-carbodithioate, benzyl 1H-pyrrole-1-carbodithioate, benzyl 1H-indole-1-carbodithioate, and benzyl 9H-carbazole-9-carbodithioate) with N -aryl group. In contrast, the polymerization with benzyl N,N -diethyldithiocarbamate cannot be controlled, and the obtained polymer has a broad molecular weight distribution or even crosslink occurs. Moreover, polymerization rate is influenced by the conjugation structure of the N -group of dithiocarbamate, and the aromatic polycyclic structure of the N -group leads to slow polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5670,5677, 2004 [source] Photopolymerization of 1,6-hexanedioldiacrylate initiated by three-component systems based on N -arylphthalimidesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2004T. Brian Cavitt Abstract Three-component photoinitiators comprised of an N -arylphthalimide, a diarylketone, and a tertiary amine were investigated for their initiation efficiency of acrylate polymerization. The use of an electron-deficient N -arylphthalimide resulted in a greater acrylate polymerization rate than an electron-rich N -arylphthalimide. Triplet energies of each N -arylphthalimide, determined from their phosphorescence spectra, and the respective rate constants for triplet quenching by the N -arylphthalimide derivatives (acquired via laser flash photolysis) indicated that an electron,proton transfer from an intermediate radical species to the N -arylphthalimide (not energy transfer from triplet sensitization) is responsible for generating the initiating radicals under the conditions and species concentrations used for polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4009,4015, 2004 [source] Influence of phenylenediamine additions on the morphology and on the catalytic effect of polyanilineJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2004Ljerka Dui Abstract The influence of para -, ortho -, and meta -phenylenediamine (p -, o -, and m -PDA) additions on the electrochemical synthesis of polyaniline has been investigated by the use of cyclic voltametry. It has been found that small additions (1 and 5 mmol L,1) of PDA monomers influence significantly the polymerization rate. Whereas p -PDA increases the polymerization rate, the addition of o - or m -PDA slows it down. Therefore, a different number of potential cycling is necessary to obtain similar thickness of layers. The layers exhibit very different morphology, which changes from "spaghetti-like" for polyaniline to "sponge-like" for p -PDA, to "pebble-like" for o -PDA and to "cauliflower-like" for m -PDA additions, respectively. The catalytic effect of the synthesized polymer layers has been tested. It has been found that all the layers exhibit catalytic effect in lowering the redox potential of hydroquinone/quinone tested reaction, but the rate of the electrocatalytic reaction varies depending on the PDA monomer added. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1599,1608, 2004 [source] Atom transfer radical polymerization of n -butyl acrylate catalyzed by CuBr/N -(n -hexyl)-2-pyridylmethanimineJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002Huiqi Zhang Abstract The homogeneous atom transfer radical polymerization (ATRP) of n -butyl acrylate with CuBr/N -(n -hexyl)-2-pyridylmethanimine as a catalyst and ethyl 2-bromoisobutyrate as an initiator was investigated. The kinetic plots of ln([M]0/[M]) versus the reaction time for the ATRP systems in different solvents such as toluene, anisole, N,N -dimethylformamide, and 1-butanol were linear throughout the reactions, and the experimental molecular weights increased linearly with increasing monomer conversion and were very close to the theoretical values. These, together with the relatively narrow molecular weight distributions (polydispersity index , 1.40 in most cases with monomer conversion > 50%), indicated that the polymerization was living and controlled. Toluene appeared to be the best solvent for the studied ATRP system in terms of the polymerization rate and molecular weight distribution among the solvents used. The polymerization showed zero order with respect to both the initiator and the catalyst, probably because of the presence of a self-regulation process at the beginning of the reaction. The reaction temperature had a positive effect on the polymerization rate, and the optimum reaction temperature was found to be 100 °C. An apparent enthalpy of activation of 81.2 kJ/mol was determined for the ATRP of n -butyl acrylate, corresponding to an enthalpy of equilibrium of 63.6 kJ/mol. An apparent enthalpy of activation of 52.8 kJ/mol was also obtained for the ATRP of methyl methacrylate under similar reaction conditions. Moreover, the CuBr/N -(n -hexyl)-2-pyridylmethanimine-based system was proven to be applicable to living block copolymerization and living random copolymerization of n -butyl acrylate with methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3549,3561, 2002 [source] Reverse atom transfer radical solution polymerization of methyl methacrylate under pulsed microwave irradiationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002Zhenping Cheng Abstract The reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) was successfully carried out under pulsed microwave irradiation (PMI) at 69 °C with N,N -dimethylformamide as a solvent and with azobisisobutyronitrile (AIBN)/CuBr2/tetramethylethylenediamine as an initiation system. PMI resulted in a significant increase in the polymerization rate of RATRP. A 10.5% conversion for a polymer with a number-average molecular weight of 34,500 and a polydispersity index of 1.23 was obtained under PMI with a mean power of 4.5 W in only 52 min, but 103 min was needed under a conventional heating process (CH) to reach a 8.3% conversion under identical conditions. At different [MMA]0/[AIBN]0 molar ratios, the apparent rate constant of polymerization under PMI was 1.5,2.3 times larger than that under CH. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3823,3834, 2002 [source] Synthesis of proton-conducting membranes by the utilization of preirradiation grafting and atom transfer radical polymerization techniquesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2002Svante Holmberg Abstract The atom transfer radical polymerization (ATRP) of styrene onto poly(vinylidene fluoride)- graft -poly(vinylbenzyl chloride) (PVDF- g -PVBC) membranes was investigated. Novel membranes were designed for fuel-cell applications. The benzyl chloride groups in the PVDF- g -PVBC membranes functioned as initiators, and a Cu-based catalytic system with the general formula Cu(n)Xn/ligand [where X is Cl or Br and the ligand is 2,2,-bipyridyl (bpy)] was employed for the ATRP. In addition, 10 vol % dimethylformamide was added for increased solubility of the catalyst complex in styrene. The system was homogeneous, except for the membrane, when the initiator/copper halide/ligand/monomer molar ratio was 1/1/3/500. As anticipated, the fastest polymerization rate of styrene was observed with the copper bromide/bpy-based catalyst system. The reaction rate was strongly temperature-dependent within the studied temperature interval of 100,130 °C. The degree of grafting increased linearly with time, thereby indicating first-order kinetics, regardless of the polymerization temperature. Furthermore, 120 °C was the maximum polymerization temperature that could be used in practice because the membrane structure was destroyed at higher temperatures. The degree of styrene grafting reached 400% after 3 h at 120 °C. Such a high degree of grafting could not be reached with conventional uncontrolled radiation-induced grafting methods because of termination reactions. On the basis of an Arrhenius plot, the activation energy for the homogeneous ATRP of styrene was 217 kJ/mol. The prepared membranes became proton-conducting after sulfonation of the polystyrene grafts. The highest conductivity measured for the prepared membranes was 70 mS/cm, which is comparable to the values normally measured for commercial Nafion membranes. The scanning electron microscopy/energy-dispersive X-ray results showed that the membranes had to be grafted through the matrix with both PVBC and polystyrene to become proton-conducting after sulfonation. In addition, PVDF- g -[PVBC- g -(styrene- block - tert -butyl acrylate)] membranes were also synthesized by ATRP. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 591,600, 2002; DOI 10.1002/pola.10146 [source] Stannous(II) trifluoromethane sulfonate: a versatile catalyst for the controlled ring-opening polymerization of lactides: Formation of stereoregular surfaces from polylactide "brushes"JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2001Michael Möller Abstract A general method for the controlled synthesis of polylactide in solution and from solid supports is presented. The evaluation of stannous(II) trifluoromethane sulfonate [Sn(OTf)2] and scandium(III) trifluoromethane sulfonate [Sc(OTf)3] as catalysts for the ring-opening polymerization (ROP) of L -, D -, and L,D -lactide is described as a route to polylactide using mild and highly selective conditions. These triflate catalysts must be used in conjunction with a nucleophilic compound such as an alcohol that is the actual initiating species via the active metal alkoxide species. Consistent with this process, 1H NMR analysis revealed that the ,-chain-end bears the ester from the initiating alcohol, and upon hydrolysis of the active metal alkoxide chain end, a ,-hydroxyl chain end was clearly detected. Polymers of predictable molecular weights and narrow polydispersities were obtained in high yields in accordance with a controlled polymerization process. The addition of base either as a solvent or additive significantly enhanced the polymerization rate with minimal loss to the polymerization control. The ROP of lactide isomers from an initiator, HO(CH2CH2O)3(CH2)11SH, self-assembled onto a gold surface using Sn(OTf)2 produced polylactide brushes under living conditions and provides the opportunity to prepare stereoregular or chiral surfaces by polymerization of enantiomerically pure monomers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3529,3538, 2001 [source] Synthesis of poly(methyl methacrylate) in a pyridine solution by atom transfer radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2001José Luis de la Fuente Abstract Pyridine was used as a solvent for the atom transfer radical polymerization (ATRP) of methyl methacrylate. The homopolymerizations were carried out with methyl 2-halopropionate (MeXPr, where X was Cl or Br) as an initiator, copper halide (CuX) as a catalyst, and 2,2,-bipyridine as a ligand from 80 to 120 °C. The mixed halogen system methyl 2-bromopropionate/copper chloride was also used. For all the initiator systems used, the polymerization reaction showed linear first-order rate plots, a linear increase in the number-average molecular weight with conversion, and relatively low polydispersities. In addition, the dependence of the polymerization rate on the temperature is presented. These data are compared with those obtained in bulk, demonstrating the effectiveness of this solvent for this monomer in ATRP. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3443,3450, 2001 [source] Photoinitiated polymerization of methacrylic monomers in a polybutadiene matrix (PB): Kinetic, mechanistic, and structural aspectsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2001J. L. Mateo Abstract The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6-hexanediol dimethacylate (HDDMA) and 2-ethylhexyl methacrylate (EHMA)] in a polybutadiene matrix (PB) have been studied. The maximum double-bond conversion, the maximum polymerization rate, the intrinsic reactivity, and the kinetic constants for propagation and termination have been calculated. Unlike the behavior followed by the SBS-HDDMA and PS-HDDMA systems, where a reaction-diffusion mechanism occurs from the start of the polymerization at low monomer concentrations (<30,40%), in the PB-HDDMA system the reaction diffusion controls the termination process only after approximately 10% conversion is reached, as for the bulk polymerization of polyfunctional methacrylic monomers. Before reaching 10% conversion the behavior observed can be better explained by a combination of segmental diffusion-controlled (autoaccelerated) and reaction-diffusion mechanisms. This is probably a consequence of the lower force of attraction between the monomer and the matrix and between the growing macroradical and the matrix than those corresponding to the other systems mentioned. For the PB-EHMA system, the termination mechanism is principally diffusion-controlled from the beginning of the polymerization for monomer concentrations below 30,40%, and for higher monomer concentrations, a standard termination mechanism takes place (kt , 106) at low double-bond conversions, which is diffusion-controlled for high conversions (>40%). For PB-HDDMA and PB-EHMA systems, crosslinked polymerized products are obtained as a result of the participation of the double bonds of the matrix in the polymerization process. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2444,2453, 2001 [source] | |||||||||||||