Polymerization of methyl methacrylate at high temperature with 1‐butanethiol as chain transfer agent

The free‐radical polymerization of methyl methacrylate (MMA) at high temperature (120 to 180°C) has been studied in the presence of di‐tertiobutyle peroxide as an initiator and 1‐butanethiol as a chain transfer agent. No solvent was used, and the polymerization was run to high monomer conversion. Based on the experimental data collected with a dilatometric reactor, the features of the reaction have been pointed out. Working at high temperature with a chain transfer agent proved efficient to reduce the intensity of the gel effect and control the molecular weight obtained. At a temperature up to 170°C, however, the burn‐out of the initiator limits the final conversion, and the increase of the polymerization rate during the gel effect has been more difficult to detect and quantify. An empirical expression of the termination rate constant has been adopted to describe the autoacceleration and predict the conversion versus time curves and the average molecular weight of the polymer obtained. The mathematical model includes two adjustable parameters that have been determined as a function of the temperature and the initial concentration of the chain transfer agent. The agreement between the predicted and experimental data on conversion and molecular weight was good, while the polydispersity index was often underestimated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1589–1599, 1999     

Size distribution of polymers during the photoinitiated free-radical copolymerization of methyl methacrylate and ethylene glycol dimethacrylate

Summary Photoinitiated methyl methacrylate-ethylene glycol dimethacrylate (MMA/EGDM) copolymerization has been investigated in toluene at a monomer concentration of 35 w/v %. Diphenyl-2,4,6-trimethylbenzoylphosphine oxide (DPTPO) was used as a photoinitiator at 0.3 wt% concentration. Monomer conversions and the size distribution of the polymer molecules were measured as a function of the reaction time up to the onset of macrogelation. Compared to the photoinitiators benzoin or benzoin derivatives, gelation process proceeds at much higher rates in the presence of DPTPO. The size distribution curves obtained by size-exclusion chromatography (SEC) change from monomodal to bimodal distributions as the polymerization proceeds. Strongly bimodal SEC curves were obtained in the close vicinity of the gel point. This finding confirms the coagulation type gelation mechanism of compact primary particles. It also indicates that the present gelation theories cannot describe the structure dependent kinetics of free-radical crosslinking copolymerization.     

Kinetic and molecular weight control for methyl methacrylate semi‐batch polymerization. I. Modelling

There are gel, glass, and cage effects in the methyl methacrylate (MMA) bulk polymerization. These effects will cause the propagation and termination rate constants and initiator efficiency change during the polymerization process, and make the kinetics and molecular weight more complex. A violent increase of conversion will bring a large amount of reaction heat evolved in a short time, and will promote temperature increase if the heat cannot be removed in time. Molecular weight of polymer will raise ten times at the same time. So, the temperature of polymerization system, kinetics of polymerization, and molecular weight and its distribution of polymer cannot be controlled. To control and unify them, the semibatch polymerization method is preferably selected. Furthermore, the kinetic and molecular weight models for MMA semibatch polymerization with the participation of chain transfer agent and new materials addition flow rate are presented. Using the presented models, the effects of temperature, initiator concentration and type, monomer or solvent concentration, and chain transfer agent concentration and type on the kinetics, and molecular weight and its distribution are simulated in this article. Experimental data of kinetics and molecular weight obtained from the published literature are compared with the simulation results to examine the presented models. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2838–2846, 2006     

Modeling of the bulk free radical polymerization up to high conversion—three stage polymerization model. II. Number-average molecular weight and apparent initiator efficiency

The equations for predicting the number-average molecular weight are derived on the basis of the three stage polymerization model (TSPM) in this paper. By applying the equations, a plotting approach is proposed to determine the apparent initiator efficiency defined as f[(α_td+1)/2] and the constant of chain transfer to monomer, where f is the initiator efficiency and α_td denotes the fraction of the termination rate constants by disproportionation. Using the approach to plot the experimental data in the literature, it is found that the chain transfer to monomer can be neglected for both methylmethacrylate (MMA) and styrene (St) polymerizations, but it can exert a significant effect on ethylmethacrylate (EMA) polymerization. In addition, the apparent initiator efficiency is found to be independent of reaction temperature and initiator concentration at each stage. The values of f[(α_td+1)/2] at gel effect stage are slightly reduced as compared with that at low conversion stage for MMA and EMA polymerizations. However, it decreases significantly at gel effect stage for St polymerization. Using the equations derived and the apparent initiator efficiencies obtained from TSPM plots, the number-average molecular weights at different conversions can be predicted. Comparisons show that the agreement between predictions and experimental data is satisfactory.     

Study on the effective process parameters influencing styrene and acrylonitrile grafting onto seeded polybutadiene latex

A series of experiments were designed and conducted to determine the significance of process parameters in the grafting of styrene and acrylonitrile onto polybutadiene seeds in a semicontinuous emulsion copolymerization system. The significances of the parameters were obtained by comparing the variance ratios, or F values, with F‐distributions. The significance level of each test (α‐value) was obtained by variance analysis. The important process parameters in industrial polymerization processes are usually monomer‐to‐polymer ratio, initiator type and concentration, chain‐transfer agent, and reaction temperature. The target responses were final monomer conversion, grafting degree, grafting efficiency, gel percent, and viscosity‐average molecular weight of free styrene‐acrylonitrile (SAN). The analysis of variance indicated that cumene hydroperoxide as the initiator and reaction temperature had strong effects on the graft structure. Moreover, free SAN molecular weight was significantly affected by the monomer/polymer ratio and cumene hydroperoxide and n‐dodecyl mercaptan as chain‐transfer agents. The raspberry‐like morphology of grafted acrylonitrile‐butadiene‐styrene (ABS) particles and phase separation within the particles were confirmed by transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

丙烯腈与丙烯酸乙酯乳液共聚合及其表征

用氧化还原引发体系在低温下研究了丙烯腈与丙烯酸乙酯的乳液共聚合。考察了聚合温度、乳化剂浓度和分子量调节剂浓度对聚合的影响 ,结果表明 ,随温度升高 ,乳化剂浓度增大 ,单体转化率和分子量增大 ,乳液更稳定 ;链转移剂十二烷基硫醇浓度增加 ,分子量显著降低 ,转化率有所降低 ,表明十二烷基硫醇在调节分子量的同时也起着缓聚剂的作用。用激光粒径分析仪考察了 2 0℃时聚合过程中乳胶粒子大小的变化 ,发现聚合过程的成核和增长均在胶束中进行的。用凝胶渗透色谱法研究了十二烷基硫醇对聚合物分子量的影响 ,发现聚合时加入分子量调节剂 ,活性链寿命较短并呈单峰分布 :聚合时不加入分子量调节剂 ,活性链寿命较长并呈双峰分布。 DSC结果表明 ,随聚合体系中软单体含量增加 ,共聚物的玻璃化温度降低。     

In-situ IR Monitoring the Synthesis of Amphiphilic Copolymery P(HEMA-co-tBMA) via ARGET ATRP

The amphiphilic copolymer poly(hydroxyethyl methacrylate-co-tert-butyl methacrylate) [P(HEMA-co-tBMA)] was synthesized by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP), with the synthesis process monitored by in-situ infrared spectroscopy (IR). The molecular weight, chemical structure and characteristics of the copolymer were determined by 1H NMR, gas chromatography and gel permeation chromatography. The influences of various parameters on the living polymerization were explored. The molecularweight of the copolymer with narrowmolecularweight distribution (M_w/M_n b 1.50) increases approximately linearly with the monomer conversion, indicating a good control of polymerization. In the reaction temperature range from 50℃ to 90℃, the monomer conversion is higher at 60℃. The tBMA conversion rate decreases gradually with the increase of tBMA content, while the HEMA conversion is hardly affected by HEMA content. Weak polar solvent is more favorable to the polymerization compared to polar solvent. The molar ratio of reducing agent to catalyst has significant effect on the polymerization and increasing the amount of reducing agent will accelerate the reaction rate but causes wider molecular weight distribution. It is indicated that in-situ IR monitoring contributes to a more in-depth understanding of the mechanism of methacrylate monomer copolymerization.     

Formation and structure of poly(methyl methacrylate) gels containing triphenyl vinyl silane

A series of Poly(methyl methacrylate) gels (PMMA) were prepared for making optical lenses by solution free radical crosslinking copolymerization of 2,2,2,‐trifluoroethyl methacrylate (TFEMA), methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), and triphenyl vinyl silane (TPVS) comonomer systems. They were then studied in toluene at a total monomer concentration of 5 molL^?1 and 70°C. The conversion of monomer, volume swelling ratio, weight fraction, and gel point were measured as a function of the TPVS concentration, temperature, and chain transfer agents up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in toluene, gel fraction, and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by Scanning electron microscopy (SEM). The dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percentage of conversion and gel fraction. Finally, TPVS is a compatible vinyl type silicone comonomer for this system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A novel strategy to branched polyacrylonitrile via one‐pot RAFT copolymerization of acrylonitrile and an asymmetrical divinyl monomer

Branched polyacrylonitriles were prepared via the one‐pot radical copolymerization of acrylonitirle and an asymmetric divinyl monomer (allyl methacrylate) that possesses both a higher reactive methacrylate and a lower reactive allyl. RAFT technique was used to keep a low‐propagation chain concentration via a fast reversible chain transfer euilibration and thus the cross‐linking was prevented until a high level of monomer conversions. This novel strategy was demonstrated to engenerate a branched architecture with abundant pendant functional vinyl and nitrile groups, and controlled molecular weight as a behavior of controlled/living radical polymerization characteristics. The effect of the various experimental parameters, including temperature, brancher to monomer molar ratio, and chain transfer agent to initiator molar ratio, on the control of moleculer dimension (molecular weight and polydispersity indices) and the degree of branching were investigated in detail. Moreover, ¹H NMR and gel permeation chromatography confirm the branched architecture of the resultant polymer. The intrinsic viscosity of the copolymer is also lower than the linear counterpart.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

自由基聚合制备甲基丙烯酸甲酯-苯乙烯嵌段共聚物

以偶氮二异丁腈为引发剂,乙二硫醇（EDT）为链转移剂进行甲基丙烯酸甲酯（MMA）的自由基聚合,得到了含有残余巯基的聚甲基丙烯酸甲酯大分子链转移剂（HS-PMMA）,继而以HS-PMMA作为大分子链转移剂进行苯乙烯的自由基聚合,采用普通自由基聚合方法合成了结构可以设计的嵌段共聚物。     

无皂乳液制备PMMA动力学及其模型

以甲基丙烯酸甲酯(MMA)为单体、过硫酸钾(KPS)为引发剂进行无皂乳液聚合反应,考察了单体MMA浓度、引发剂KPS用量及聚合温度对其动力学行为的影响。建立了转化率-时间关系曲线的模型函数———Gamm a积分函数,用它拟合了转化率-时间关系曲线,获得了聚合过程的重要特征参数,如平均成核速率,聚合最大速率和平稳期平均聚合速率及成核结束和聚合进入完成期对应的转化率。同时对聚合速率与以上各聚合参数的关系数据进行了非线性拟合,得到了它们之间的关系式。拟合相关系数非常接近于1,平均拟合误差很小,成核结束时转化率在15%以内,聚合速率随以上参数增大而增大,反应温度在聚合过程中起决定作用。     

Kinetics of the free-radical copolymerization of methyl methacrylate/ethylene glycol dimethacrylate: 1. Experimental investigation

An experimental investigation was made of the kinetics of the bulk free-radical copolymerization of methyl methacrylate (MMA) and the divinyl monomer ethylene glycol dimethacrylate (EGDMA) initiated with AIBN at 70°C for levels of EGDMA of 0–25 wt% and chain transfer agent (CBr₄) levels of 0–1 wt%. The conversion of monomers to sol and crosslinked gel was measured by gravimetry using Soxhlet extraction. This provided measurements of monomer conversion at the gelation point as a function of EGDMA and CBr₄ levels and the weights of sol and gel as a function of time and monomer conversion. The experimental data are interpreted in terms of the pseudo-kinetic rate constant method in Part 2 of this series.     

Effects of cyclization and pendant vinyl group reactivity on the swelling behavior of polyacrylamide gels

A series of polyacrylamide (PAAm) gels were prepared by free-radical crosslinking copolymerization of acrylamide and N,N′-methylenebis(acrylamide) (BAAm) in water at various crosslinker (BAAm) and chain transfer agent (isopropyl alcohol, IPA) concentrations. It was shown that only 5% of the crosslinker used in the feed forms effective crosslinks in the final hydrogels. At BAAm contents as high as 3 mole%, the equilibrium swelling ratio of the gels in water is independent of the crosslinker content in the feed. This is due to the prevailing multiple crosslinking reactions during the gel formation process. At a fixed crosslinker content, the onset of gelation is shifted towards higher conversions and reaction times as the amount of IPA increases. Addition of IPA in the monomer mixture also increases the equilibrium swelling ratio of PAAm gels. It was shown that the gel crosslinking density increases on rising IPA concentration in the feed due to the increasing rate of intermolecular crosslinking reactions. Received: 30 May 1997/Accepted: 26 June 1997     

苯乙烯热引发本体聚合的动力学研究 1 转化率与时间的关系

基于三段聚合模型 (TSPM) ,研究了 10 0— 2 0 0℃苯乙烯 (St)热引发本体聚合。结果表明 ,TSPM同样适用于描述 St热引发本体聚合。用文献中发表的大量实验数据进行 TSPM标绘表明 ,由低转化阶段向凝胶效应阶段转变时的临界转化率 x1与聚合温度无关 ,为一定值 ,大致等于 0 .5。同时 ,聚合各阶段的表观速率常数可用阿累尼乌斯 (Arrhenius)方程关联。用得到的表观速率常数计算方程和 x1,对转化率与时间关系进行了计算 ,并与文献中发表的大量实验数据作了比较。结果表明 ,二者较为吻合     

高固含量聚丙烯酰胺反相微乳液的制备

研究了高单体质量分数(25%～40%)下丙烯酰胺的反相微乳液聚合反应,使用工业白油作为分散介质,使用复合非离子乳化剂稳定反应体系,使用焦亚硫酸钠引发聚合。研究了引发剂组成及浓度、交联剂浓度、温度及单体浓度对反应转化率和聚合物分子质量的影响。结果表明,转化率和分子质量主要受引发剂浓度及单体浓度的影响。根据筛选出来的优化条件,制备了固含量接近40%、分子质量约850万的聚丙烯酰胺微乳液。     

Preparation and properties of silicone‐containing poly(methyl methacrylate) gels

Poly(methyl methacrylate) (PMMA) gels with varying amounts of silicone and solvent and constant amounts of crosslinker were prepared by solution free radical crosslinking copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) comonomer systems. They were then studied in benzene at a total monomer concentration of 3.5 mol L^?1 and 70 °C. The conversion of monomer, volume swelling ratio, weight fraction and gel point were measured as a function of the reaction time, silicone concentration and benzene content up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in benzene, gel fraction and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by SEM. Based on the obtained results, it was concluded that the FTIR data did not have the capacity to show the presence of the VTES or TEOS moiety in these kinds of copolymers. On the other hand, the variation of weight fraction of gel, W_g, and its equilibrium volume swelling ratio in benzene, q_v, exhibited the same behaviour as that of MMA/EGDM copolymers. Also, the dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percent of conversion and gel fraction. Finally, TEOS is not an ideal silicone compound for reaction in the MMA/EGDM copolymerization system, whereas VTES is a suitable silicone comonomer for this system and it has been proved useful. Copyright © 2005 Society of Chemical Industry     

Factorial experimental design for graft copolymerization of styrene and methyl methacrylate onto styrene–butadiene rubber

The graft copolymerization of styrene (ST) and methyl methacrylate (MMA) onto styrene–butadiene rubber (SBR) latex prepared by seeded emulsion polymerization has been studied under various reaction conditions using cumene hydroperoxide redox initiator. The mechanism of graft copolymerization has been investigated. The synthesized graft copolymers were purified and then characterized by proton nuclear magnetic resonance (¹H NMR) analysis. A 2 2 fractional factorial experimental design was applied to study the effects of the process variables such as the amount of initiator and emulsifier, the presence or absence of chain‐transfer agent, ST to MMA ratio, monomer to rubber ratio, and reaction temperature on the grafting efficiency. The analysis of the results from the design showed the sequence of the main effect on the observed response of the grafting of ST and MMA onto SBR and that the amount of chain‐transfer agent had a significant effect. Transmission electron microscopy was used to study the morphology of the graft copolymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2867–2874, 2006     

超声波辅助引发MAA/AN自由基共聚合研究

考察了超声波辅助甲基丙烯酸(MAA)和丙烯腈(AN)共聚合时,单体配比、引发剂浓度、超声波频率以及超声场温度对体系转化率的影响。结果表明,超声波能够辅助MAA/AN进行本体聚合,加快聚合反应速率。超声波辐照下,本体聚合的转化率随反应温度的升高而增大,引发剂用量为0.2%时,反应的转化率最大。外加能量的超声波利于加快聚合反应速率,在频率为24 kHz的超声波辐照下,对提高共聚反应转化率的作用最大。     

沉淀聚合制备低分子量聚丙烯酸及残液循环利用

以偶氮二异丁腈(AIBN)为自由基引发剂,石油醚为溶剂,异丙醇为链转移剂,通过沉淀聚合制备了低相对分子质量(简称分子量,下同)的聚丙烯酸。考察了引发剂用量、链转移剂用量、单体质量浓度对聚合收率的影响,确定最佳聚合条件为:AIBN用量为单体质量的10%,链转移剂用量为单体质量的100%,单体质量浓度100g/L,反应温度80℃,反应时间4 h。反应结束后产品在底部沉淀析出,溶剂可循环利用,在最佳聚合条件下,残液循环利用5次,单体的累计转化率达到92.6%。凝胶渗透色谱(GPC)分析表明,通过残液循环制备的产品重均分子量(Mw)变化不大,保持在1 000～1 300,多分散性(PDI)为1.92～3.38。     

Atom transfer radical copolymerization of methyl methacrylate with N‐cyclohexylmaleimide

Atom transfer radical polymerization has been applied to simultaneously copolymerize methyl methacrylate (MMA) and N‐cyclohexylmaleimide (NCMI). Molecular weight behaviour and kinetic study on the copolymerization with the CuBr/bipyridine(bpy) catalyst system in anisole indicate that MMA/NCMI copolymerization behaves in a ‘living’ fashion. The influence of several factors, such as temperature, solvent, initiator and monomer ratio, on the copolymerization were investigated. Copolymerization of MMA and NCMI in the presence of CuBr/bpy using cyclohexanone as a solvent instead of anisole displayed poor control. The monomer reactivity ratios were evaluated as r_NCMI = 0.26 and r_MMA=1.35. The glass transition temperature of the resulting copolymer increases with increasing NCMI concentration. The thermal stability of plexiglass could be improved through copolymerization with NCMI. © 2000 Society of Chemical Industry