Kinetics of the styrene emulsion polymerization using n‐dodecyl mercaptan as chain‐transfer agent

The kinetics of the styrene emulsion polymerization using n‐dodecyl mercaptan as chain‐transfer agent was studied. It was found that the chain‐transfer agent (CTA) had no effect on polymerization rate but substantially affected the molecular weight distribution (MWD). The efficiency of the CTA in reducing the MWD was lowered by the mass‐transfer limitations. The process variables affecting CTA mass transfer were investigated. A mathematical model for the process was developed. The outputs of the model include monomer conversion, particle diameter, number of polymer particles, and number‐average and weight‐average molecular weights. The model was validated by fitting the experimental data. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4490–4505, 2000     

Living radical miniemulsion polymerization by RAFT in the presence of beta-cyclodextrin

Living radical polymerization of styrene in a miniemulsion by reversible addition–fragmentation chain transfer (RAFT) was successfully realized in the presence of beta-cyclodextrin (CD), using sodium dodecyl sulfate and hexadecane as surfactant and costabilizer, respectively. The drawback of instability (red layer formation) encountered in the living radical polymerization in emulsion or miniemulsion was overcome. The linear relationship between the monomer conversion and the molecular weight, as well as lower molecular weight distribution (MWD), shows that the polymerization process was under control. The addition of CD was found to have little influence on the polymerization rate. However, MWD of the polymer synthesized is obviously decreased. The mechanism of stability and controllability improvement in the presence of CD proposed that the complex formation between CD and RAFT agent or RAFT agent-ended oligomer increased their diffusion ability from monomer droplet to polymerization locus and improved the homogeneity of the RAFT agent level among the polymerization loci.     

Gamma-ray induced polymerization of styrene in the presence of methanol

The kinetics and molecular weight distributions (MWD) of the gamma-ray induced polymerization of styrene in methanol were studied at 35°C, at low conversions and over a dose rate range of 2.76 × 10³ to 2.74 × 10⁴ rad/hr. The data obtained at low initial methanol content agreed with previously obtained results and the MWD of the polystyrene formed yielded a single unimodal peak with M?_n in the range of 35,000–480,000. However, at high initial methanol content and low dose rates, at least three peaks were clearly discernible over wide molecular weight distributions. The existence of these peaks is related to the kinetic data and the formation of three distinguishable regions in the polymerization system.     

Emulsion polymerization of styrene using irreversible addition–fragmentation chain transfer agents: effect on the course of the polymerization and molecular weight

The emulsion polymerization of styrene with three different chain transfer agents (CTAs) based on irreversible addition–fragmentation chain transfer (AFCT) mechanism was first reported in this work. The influences of these irreversible AFCT agents on the rate of polymerization, particle size, and molecular weight were investigated. It was found that the intrinsic activity and desorption behaviors of the CTAs determined the efficiency for molecular weight control, rate of polymerization, and particle size in the emulsion polymerization. It has been demonstrated that the rate of polymerization and particle size decreased dramatically in the presence of the irreversible AFCT agents with high chain transfer constant (ethyl α-p-toluenesulfonyl-methacrylate), meanwhile, the molecular weight of the polystyrene could not be controlled well, whereas the irreversible AFCT agents with low chain transfer constant (butyl(2-phenylallyl)sulfane and 2,3-dichloropropene) had a slight effect on the polymerization rate, particle size, and were fairly well for molecular weight control over the whole conversion range in the emulsion polymerization of styrene. The average number of radicals per particle and the number-average molecular weight were calculated by classical radical emulsion polymerization theory, and the experimental results were in good agreement with the results of model calculations, when the irreversible AFCT agents were used as CTAs. The effect of chain transfer agents on the kinetics and nucleation in the emulsion polymerization of styrene can be attributed to desorption of chain-transferred radicals from the polymer particles. The results of this work show that butyl(2-phenylallyl)sulfane as CTA in emulsion polymerization of styrene provides the best balance between the rate of polymerization and the efficiency for molecular weight control conflicting tendencies.     

Kinetics of heterogeneous atom transfer radical polymerization of styrene by using bis(1,10‐phenanthroline)copper bromide

The kinetics of atom transfer radical polymerization (ATRP) of styrene using bis(1,10‐phenanthroline)copper bromide was investigated. The concentration of the copper catalyst does not affect the propagation rate but does affect the termination process of polymerization appreciably. With increasing reaction temperature the molecular weight distribution of the produced PS becomes more narrow. The apparent activation energy was found to be 75 kJ/mol.     

Atom-transfer radical polymerization of styrene with bifunctional and monofunctional initiators: Experimental and mathematical modeling results

Bulk atom transfer radical polymerization (ATRP) of styrene was carried out at 110 °C using benzal bromide as bifunctional initiator and 1-bromoethyl benzene as monofunctional initiator. CuBr/2,2′-bipyridyl was used as the ATRP catalyst. The polymerization kinetic data for styrene with both initiators was measured and compared with a mathematical model based on the method of moments and another one using Monte Carlo simulation. An empirical correlation was incorporated into the model to account for diffusion-controlled termination reactions. Both models can predict monomer conversion, polymer molecular weight averages, and polydispersity index. In addition, the Monte Carlo model can also predict the full molecular weight distribution of the polymer. Our experimental results agree with our model predictions that bifunctional initiators can produce polymers with higher molecular weights and narrower molecular weight distributions than monofunctional initiators. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2212–2224, 2007     

吡啶类试剂调节H_2O/TiCl_4引发苯乙烯正离子聚合研究

1988年,Kennedy等[1~3]首先实现了由BCl3共引发的苯乙烯(St)及其衍生物活性正离子聚合,但所得到聚合产物的分子量分布宽(Mw/Mn=5~6).苯乙烯活性正离子聚合的共引发剂由BCl3扩展到SnCl4、TiCl4[4~7]和TiCl3(OiPr).对于TiCl4共引发的St活性正离子聚合,所用引发剂为2,4,4-三甲基-2     

Diffusion mechanism of water vapour in a zeolitic tuff rich in clinoptilolite

The adsorption kinetics of H₂O in a clinoptilolite rich zeolitic tuff was experimentally investigated at 18°C. In the identification of the diffusion mechanism the isothermal adsorption model equation was used. It was found out that the intraparticle mass transfer becomes more dominant over the heat transfer with increase in particle size and the adsorptive dose pressure. Although initially intraparticle mass transfer was the controlling resistance later external heat transfer also contributes to the transfer mechanism.     

Effect of Nanoclay on Styrene and Butyl Acrylate AGET ATRP in Miniemulsion: Study of Nucleation Type,Kinetics, and Polymerization Control

Poly(styrene‐co‐butyl acrylate)/clay nanocomposites were synthesized in miniemulsion via activators generated by electron transfer (AGET) for atom transfer radical polymerization (ATRP). Optimum amounts of catalyst and reducing agent were chosen by considering a linear increase in ln([M₀]/[M]) versus time, narrow molecular distribution, and low polydispersity index (PDI). Critical micelle concentration and cross‐sectional surface area per surfactant head group were determined by surface tension analysis. Calculations show that droplet nucleation is the dominant mechanism of nucleation in a miniemulsion system, and there is no micelle in the system. Gel permeation chromatography was used to characterize molecular weight, PDI, and molecular weight distribution. After determination of appropriate conditions, poly(styrene‐co‐butyl acrylate)/clay nanocomposite latexes were synthesized. Low PDI, narrow molecular weights, and first‐order kinetics of the nanocomposites justify that polymerization is well controlled. Kinetics of polymerization decreases by clay loading. The apparent propagation rate constant (k_app) of polymerization in the case of poly(styrene‐co‐butyl acrylate) is 4.079 × 10^?6, which becomes 0.558 × 10^?6 in the case of poly(styrene‐co‐butyl acrylate)/clay nanocomposite with 2% nanoclay. A decrease in the polymerization rate is related to the hindrance effect of nanoclay layers on monomer diffusion toward the loci of growing macroradicals.     

Coupled Single‐Particle and Population Balance Modeling for Particle Size Distribution of Poly(propylene) Produced in Loop Reactors

A comprehensive model was developed for the PSD of PP produced in loop reactors. The polymeric multilayer model (PMLM) was first applied to calculate the single particle growth rate under intraparticle transfer limitations. In order to obtain the comprehensive model, the PMLM was solved together with a steady‐state particle population equation to predict the PSD in the loop reactors. The simulated PSD data obtained under steady‐state polymerization conditions agreed with the actual data collected from industrial scale plant. The comprehensive model was also used to predict the effects of some critical factors, including the intraparticle mass and heat transfer limitations, the feed catalyst particle size and the catalyst deactivation, etc., on the PSD.

     

不同结构Iniferter引发苯乙烯聚合反应的研究

以不同结构的含氯化合物与铜试剂反应合成了4种链引发-转移-终止剂(Iniferter)。研究了它们引发苯乙烯的聚合反应过程,重点考察了Iniferter结构对聚合产物的影响。采用核磁共振氢谱和凝胶渗透色谱对聚合物分子量和分子量分布进行了测定。结果表明:Iniferter结构对聚合反应速率、分子量实测值与理论值间的对应关系及分子量分布均有明显影响,当其形成的初级自由基上带有使其稳定的基团时,引发效率就高,聚合反应速率较快,而且分子量理论值与实测值两者更接近。加入四甲基秋兰姆化二硫组成双组份Iniferter引发体系可以在一定程度上使聚合物分子量分布变窄。     

苯乙烯Ziegler-Natta聚合扩散控制动力学研究

本文研究苯乙烯在TiCl_3-Al(C_2H_5)_3催化下于甲苯、正庚烷或甲苯-正庚烷混合物介质中的聚合动力学。提出了一个含催化剂球形聚合物颗粒中发生单体扩散控制聚合的模型,导出的式子统一解释了不同介质中扩散阻力造成的不同程度的速率表减,定量说明了在聚笨乙烯良溶剂中聚合时扩散阻力小于在不良溶剂中时。     

H_2O/TiCl_4/Py体系引发苯乙烯正离子聚合

研究了在少量吡啶(Py)存在下由水(H2O)四氯化钛(TiCl4)体系引发苯乙烯于二氯甲烷正己烷中进行碳正离子聚合,分别考察[Py]、[H2O]和[TiCl4]对聚合速率、产物分子量与分子量分布的影响.实验结果表明,少量亲核试剂吡啶(Py)对聚合反应起着重要作用,可有效地降低聚合速率和使分子量分布变窄;随着[H2O]和[Py]降低或[TiCl4]增加,聚合产物的分子量增加,而分子量分布指数(Mw Mn)基本维持在1.8左右;随着[Py]增加,聚合速率降低;随着[H2O]和[TiCl4]增加,聚合速率提高.聚合速率对单体浓度呈一级动力学关系,对Py、H2O和TiCl4的反应级数分别为-0.72、0.72和1.86.聚合速率对TiCl4浓度呈接近二级动力学关系,这可能与体系中TiCl4主要以二聚体形式存在有关.聚合转化率和产物分子量均随着反应时间延长而逐渐增大,PS的数均分子量与转化率呈线性增加关系.     

Kinetic modeling of two-step RAFT process for the production of novel fluorosilicone triblock copolymers

Well-defined poly(dimethylsiloxane)-b-poly(2,2,3,3,4,4,4-heptafluorobutylmethacryl-ate-b-poly(styrene) (PDMS-b-PHFBMA-b-PS) triblock copolymers were prepared by two-step reversible addition-fragmentation chain transfer (RAFT) polymerization. A comprehensive mathematical model for the two-step RAFT polymerization in a batch reactor was presented using the method of moments. The model described molecular weight, monomer conversion and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the suggested model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration and monomer concentration on the two-step RAFT polymerization kinetics. The simulated results showed that for the two-step RAFT polymerizations, the effects initiator concentration, chain transfer agent concentration and monomer concentration are identical and the influence degrees are different yet.     

Kinetic study of the mass transfer of bovine serum albumin in anion-exchange chromatography

A kinetic study was made on the mass transfer phenomena of bovine serum albumin (BSA) in two different anion-exchange columns (Resource-Q and TSK-GEL-DEAE-5PW). The analysis of the concentration dependence of the lumped mass transfer rate coefficient (km,L) provided the information about the kinetics of the several mass transfer processes in the columns and the anion exchangers, i.e., the axial dispersion, the fluid-to-particle mass transfer, the intraparticle diffusion, and the adsorption/desorption. In the Resource-Q column, the intraparticle diffusion had a dominant contribution to the band broadening compared with those of the other processes. The surface diffusion coefficient (Ds) of BSA showed a positive concentration dependence, by which the linear dependence of km,L on the BSA concentration seemed to be interpreted. On the other hand, in the TSK-GEL-DEAE-5PW column, the contribution of the adsorption/desorption was also important and almost same as that due to the intraparticle diffusion. There are some differences between the intrinsic properties of the mass transfer kinetics inside the two anion exchangers. It was likely that the positive concentration dependence of Ds was explained by the heterogeneous surface model.     

球形MgCl_2负载钛催化剂催化苯乙烯等规聚合与产物分子量分布研究

采用球形高效负载ZieglerNatta催化体系(TiCl4MgCl2AlR3二苯基二甲氧基硅烷(DPDMS)合成等规聚苯乙烯(iPS),催化效率最高可达7.7×103gPSgTi·h.通过多个SchulzFlory最可几分布对产物的分子量分布曲线拟合分峰来研究iPS的分子量及分子量分布的变化,AlEt3能使产物中低分子量部分含量增加,Al(iBu)3则倾向于形成高分子量的活性中心.体系中加入氢气不仅能显著提高催化效率,而且使iPS的分子量分布显著增宽.     

Kinetic study of in situ normal and AGET atom transfer radical copolymerization of n–butyl acrylate and styrene: Effect of nanoclay loading and catalyst concentration

The effect of clay nanolayers and catalyst concentration on the kinetics of atom transfer radical copolymerization of styrene and butyl acrylate initiated by activators generated by electron transfer (AGET initiation system) or an alkyl halide (normal initiation system) was studied. Monomer conversion was studied by attenuated total reflection–Fourier transform infrared spectroscopy, and also proton nuclear magnetic resonance (¹H NMR) spectroscopy was utilized to evaluate the heterogeneity in the composition of poly(styrene‐co‐butyl acrylate) chains. A decrease in the copolymerization rate of styrene and butyl acrylate in the presence of clay platelets was observed since clay layers confine the accessibility of monomer and growing radical chains. Considering the linear first‐order kinetics of the polymerization, successful AGET and normal atom transfer radical polymerization (ATRP) in the presence of clay nanolayers were carried out. Consequently, poly(styrene‐co‐butyl acrylate) chains with narrow molecular weight distribution and low polydispersity indices (1.13–1.15) were obtained. The linearity of ln([M]₀/[M]) versus time and molecular weight distribution against conversion plots indicates that the proportion of propagating radicals is almost constant during the polymerization, which is the result of insignificant contribution of termination and transfer reactions. Controlled synthesis of poly(styrene‐co‐butyl acrylate)/clay is implemented with the diminishing catalyst concentration of copper(I) bromide/N,N,N′,N′′,N′′‐pentamethyl diethylene triamine without affecting the copolymerization rate of normal ATRP. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 789–799, 2012     

Sorption of basic dyes onto granulated pillared clays: thermodynamic and kinetic studies

Effect of the granulation process onto the thermodynamic and kinetic sorption parameters of two basic dyes (Basic Yellow 28-BY 28 and Basic Green 4-BG 4) was evaluated in the present work. The charge surface properties of the surfactant-modified aluminium-pillared clay (CTAB-Al-Mont-PILC) particles were not modified, and the isoelectric point remains constant after high shear wet granulation. The Gibbs free energy of both BY 28 and BG 4 sorption was negative and decreased with the granulation; the endothermic nature of the sorption process was confirmed by the positive values of ΔH°. Adsorption kinetics of the two dyes, studied at pH 6 and 150 mg L(-1), follow the pseudo-first order kinetic model with observed rate constants of 2.5-4.2×10(-2) min(-1). The intraparticle diffusion model, proposed by Weber and Morris, was applied, and the intraparticle plots revealed three distinct sections representing external mass transfer, intraparticle diffusion and adsorption/desorption equilibrium. Diffusion coefficients, calculated from the Boyd kinetic equation, increased with the granulation and the particle size. Pseudo-first order kinetic constants, intraparticle diffusion rate constants and diffusion coefficients were determined for two other initial concentrations (50 and 100 mg L(-1)) and include in a statistical study to evaluate the impact of granulation and initial concentration on the kinetic parameters. Kruskal-Wallis tests, Spearman's rank order correlation and factor analysis revealed a correlation between (i) the diffusion coefficients and granulation, and between (ii) the intraparticle diffusion rate constants and initial concentration.     

Studies on the atom transfer radical polymerization of a maleimide AB* monomer and modification of the halogen end groups

The atom transfer radical polymerization (ATRP) of an AB* monomer, N-(4-α-bromobutyryloxy phenyl)maleimide (BBPMI), was conducted using the complex of CuBr/2,2′-bipyridine as catalyst. The study of kinetics of polymerization and the growth behavior of macromolecules show that the polymerization proceeds rapidly in first 1 h and then slows down. The decrease in the rate of polymerization is ascribed to the poor reactivity of maleimide radicals from A* to initiate the polymerization of maleimide double bonds. The molecular weight of the resulting polymer also increases with the dosage of catalyst. The coincidence of molecular weight determined by hydrogen proton nuclear magnetic resonance spectroscopy (¹H NMR) and gel permeation chromatography (GPC) proves that the resulting polymer is of linear structure, which is further verified by ¹³C NMR measurement and high performance liquid chromatography (HPLC) analysis of the hydrolysate of the resulting polymer. The stabilization modification of the halogen end groups of the resulting polymer by free-radical chain transfer reaction was attempted under ATRP condition. Isopropyl benzene was employed as the chain transfer agent. Indeed, the modified polymer with carbon-bromine bonds conversion of 40.7% shows enhanced thermal stability. The initial weight loss temperature has been increased from 193 to 243 °C. On the other hand, the atom transfer radical copolymerization of BBPMI with styrene resulted in the formation of hyperbranched polymer.     

Studies on propagating species in cationic polymerization of styrene derivatives by acetyl perchlorate or iodine. IV. Common-ion salt effect on the polymerization rate and the steric structure of the polymer obtained by acetyl perchlorate

Effects of a common-ion salt, n-Bu₄NClO₄, on the cationic polymerization of styrene and p-chlorostyrene by acetyl perchlorate were studied in a variety of solvents at 0°C. In polymerization (in CH₂Cl₂) which yielded polymers with a bimodal molecular weight distribution (MWD), addition of the salt suppressed the formation of higher polymers, but affected neither the molecular weight nor the steric structure of the lower polymers. The polymerization rate decreased with increasing salt concentration and became constant at or above a certain concentration. In nitrobenzene, on the other hand, the MWD of the polymers was unimodal and steric structure was unchanged even in the presence of salt at a concentration 50 times that of the catalyst. However, the polymerization rate and the polymer molecular weight decreased monotonically as salt concentration increased. On the basis of these results, it was concluded that the ion pair in methylene chloride differs from that in nitrobenzene, and that the species in the latter solvent is similar in nature to free ions. The fractional contribution of the dissociated and nondissociated propagating species to polymer formation was determined from the rate depression caused by addition of the salt.