表面活性单体存在下的MMA/BA乳液共聚合(Ⅱ)聚合动力学及机理

研究了表面活性单体[磺化-十二醇-烯丙基甘油-丁二酸酯钠盐(ZC-L)]的用量对MMA/BA/ZC-L乳液聚合速率和粒径的影响,用CoulterLS230型激光粒径分析仪测定聚合过程中乳液的粒径和粒径分布变化,并与MMA/BA无皂乳液聚合及十二烷基苯磺酸钠存在下的MMA/BA乳液聚合作了比较.[ZC-L]CMC时,成核机理包括均相成核和胶束成核机理,生成的粒子因吸收体系中的表面活性单体而稳定存在.     

MMA/BA无皂乳液聚合机理研究--三阶段成粒机理

用Coulter LS230激光粒径分析仪研究MMA/BA无皂乳液共聚合中单分散粒子的成粒机理.根据理论和实验数据分析,其成核过程为均相成核机理.根据粒径分布和粒子数变化情况,把无皂乳液聚合过程分为3个阶段:第一阶段为成核-凝聚阶段,体系粒子数密度迅速增加,而粒径变化较小;第二阶段为成核-凝聚、增长-聚并共存阶段,当粒子数密度开始快速减少时,标志着第一阶段结束,第二阶段开始,当初级粒子开始消失时,标志着第二阶段结束;第三阶段为增长-聚并阶段.成核过程结束后,粒子迅速增长,较小粒子在增长过程中的优先聚并,导致粒径逐渐趋向均一,最终生成单分散性乳液.     

表面活性单体存在下的MMA／BA乳液共聚合（Ⅱ）：聚合动力？…

研究了表面活性单体「磺化－十二醇－烯丙基甘油－丁二酸酯钠盐（ＺＣ－Ｌ）」的用量对ＭＭＡ／ＢＡ／ＺＣ－Ｌ乳液聚合速率和粒径的影响,用Ｃｏｒｌｔｉｒ ＬＳ２３０型激光粒径分析仪测定聚合过程中乳液的粒径和粒径分布变化,并与ＭＭＡ／ＢＡ无皂乳液聚合及十二烷基苯磺酸钠存在下的ＭＭＡ／ＢＡ乳液聚合作了比较。「ＺＣ－Ｌ」〈ＣＭＣ时,成核机理为均相成核机理,乳胶粒需依靠粒子间的凝聚来提高表面电荷密度而稳定;「ＺＣ     

悬浮-乳液复合聚合聚苯乙烯-聚甲基丙烯酸甲酯复合粒子的颗粒特性和成粒机理

采用在苯乙烯 (St)悬浮聚合过程中滴加甲基丙烯酸甲酯 (MMA)乳液聚合组分的悬浮 乳液复合聚合方法 ,制备大粒径聚苯乙烯 聚甲基丙烯酸甲酯 (PS PMMA)复合粒子 .研究聚合物粒径分布和颗粒形态的变化发现 ,在St悬浮反应中期滴加MMA乳液聚合组分后 ,聚合体系逐渐由悬浮粒子与乳胶粒子并存向形成单峰分布复合粒子转变 ,最终形成核 壳结构完整的大粒径PS PMMA复合粒子 ;在St悬浮反应初期滴加MMA乳液聚合组分 ,St与MMA一起分散成更小液滴 ,反应后期凝并成非核 壳结构复合粒子 ;在St悬浮反应后期滴加MMA乳液聚合组分 ,PMMA乳胶粒子与PS悬浮粒子基本独立存在 .根据以上结果 ,提出了St MMA悬浮 乳液复合聚合的成粒机理 .     

种子乳液聚合的研究进展

种子乳液聚合法因具有乳液稳定性更好、粒径分布窄、易控制等优点,在乳胶粒子设计及制备各种功能性胶乳方面具有重要作用,是制备高固含量乳液及具有核壳结构乳液的最常见最简便的方法.本文综述了近年来种子乳液的聚合工艺、聚合机理, 包括接枝机理、互穿聚合物网络机理、聚合物沉积机理、种子表面聚合机理和离子键合机理等,以及种子乳液聚合在乳胶粒子设计方面的应用研究进展,并讨论了影响种子乳液聚合的各种因素.     

新型乳液聚合制备疏松PMMA树脂及成粒机理

采用以水相为分散相、甲基丙烯酸甲酯 (MMA) 环己烷混合物为连续相的新型乳液聚合制备PMMA树脂 .发现 ,在未加乳化剂和加入少量Tween2 0乳化剂时 ,均可制备由初级粒子凝聚而成、无明显皮膜结构的疏松PMMA粒子 ,初级粒子粒径小于环己烷存在下MMA悬浮聚合得到的PMMA粒子的初级粒子 .根据聚合体系相构成、PMMA在MMA 环己烷混合液的溶解性及PMMA粒子粒径分布和形态的演变 ,提出了在分散水滴内乳液聚合形成初级粒子 生长 凝聚的新型乳液聚合成粒机理     

聚硅氧烷/丙烯酸酯核/壳复合胶乳的粒径分布与成核机理

通过种子乳液法合成出具有高有机硅含量核 壳结构的聚硅氧烷 丙烯酸酯复合粒子 .研究了聚合方法、乳化剂浓度、引发剂浓度、单体滴加速度等工艺条件对复合乳液粒径尺寸、分布与形态的影响 ,并对复合乳液的成核机理进行了探讨 .研究表明 ,乳化剂浓度对乳液粒子的粒径分布和形态、结构有显著影响 ,引发剂浓度增加将使粒子粒径减小 ;相对一次投料法 ,种子乳液法生成的粒子分布窄 ,具有明显核壳结构 ,通过壳层单体滴加速度可以控制粒子的粒径尺寸和分布 ;而壳层丙烯酸酯聚合物主要是在聚硅氧烷种子表面的“过渡层”聚合、富集而成 .     

MMA／BA无皂乳液聚合机理研究——三阶段成粒机理

用Ｃｏｕｌｔｅｒ ＬＳ２３０激光粒径分析仪研究ＭＭＡ／ＢＡ无皂乳液共聚合中单分散粒子的成粒机理。根据理论和实验数据分析,其成核过程为均相成核机理。根据粒径分布和凿子数变化情况,把无皂乳液聚合过程分为３个阶段,第一阶段为成核－凝聚阶段,体系粒子数密度迅速增加,而粒径变化较小;第二阶段为成核－凝聚,增长 －聚并共存阶段,当粒子数密度开始快速减少时,标志着第一阶段结束,第二阶段开始,当初级凿子开始消失时     

MMA/BA种子半连续乳液聚合成核过程及机理研究

引入一种不溶于水的染色剂(BL-S)作示踪剂,研究甲基丙烯酸甲酯(MMA)/丙烯酸丁酯(BA)种子半连续乳液聚合中各变量对成核过程及成核机理的影响,运用最终乳胶粒中染色剂的含量(Pdye)、最终乳胶粒子数(Npc)、胶束成核和均相成核所形成的粒子数目(Nm和Nh)等参数对聚合过程中的成核情况进行定量分析.结果发现,当引发剂浓度[I]增大时,Pdye、Nh、Nm和Nh/Npc均随之增大,同时Nm/Npc相应地减小,且Nm/Npc=-0.0262[I]+0.8833,表明均相成核随[I]的增大而增加,但胶束成核的比例减小.乳化剂浓度[E]在不同范围内对成核机理的影响不同,在[E]=0.7216×10-2mol.L-1时,体系中胶束成核和均相成核比例相等,各为50%;当[E]>0.7216×10-2mol.L-1时,随[E]增大,成核时间t1,2逐渐缩短,Nm/Npc增加,Nh/Npc减小,胶束成核所占比例大于均相成核,胶束成核逐渐上升为主要成核方式;反之当[E]<0.7216×10-2mol.L-1时,体系中胶束成核所占比例小于均相成核,均相成核为主要成核方式.当MMA的摩尔分率fMMA由0增至0.6时,Nm/Npc从80.93%下降至50%,体系中以胶束成核为主,均相成核为辅;当fMMA由0.6增至1时,Nm/Npc已降至40%,而Nh/Npc增至60%,体系中已转变成均相成核为主,胶束成核为辅.在常规和种子半连续乳液聚合中,t1,2分别为12min和6min,而Pdye变化较小,表明聚合方式只影响粒子的形成过程和成核时间的长短,对成核方式影响甚微.     

聚合过程中原位生成助稳定剂的细乳液聚合

以甲基丙烯酸十二氟庚酯(DFMA)、甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)为共聚单体,不加任何传统的助稳定剂进行细乳液聚合.在共聚体系中,由于DFMA在初期反应生成的聚合物中占有较高比例,初期形成的少量低聚物可以起到助稳定剂作用,因此DFMA作为反应单体的同时,又可以原位生成助稳定剂,维持单体液滴或乳胶粒子的稳定,以细乳液聚合的方式进行聚合.分别采用油溶性引发剂(AIBN)和水溶性引发剂(KPS)引发聚合,考察细乳液聚合过程中乳胶粒子粒径的变化规律,粒径由初始时刻的400nm左右减少到80nm左右,最终与使用传统的助稳定剂得到的粒径相当.提出了原位生成助稳定剂的细乳液聚合机理,并使用交联剂验证了提出的原位生成助稳定剂的细乳液聚合机理.     

STUDY ON THE FORMATION MECHANISM OF MONODISPERSE PARTICLES IN THE EMULSIFIER-FREE EMULSION POLYMEAIZATION OF METHYL METHACRYLATE AND BUTYL ACRYLATE

The formation mechanism of monodisperse polymer latex particles in the emulsifier-free emulsion polymerizationof methyl methacrylate and butyl acrylate with potassium persulfate as initiator was investigated. A multi-step formationmechanism for the monodisperse polymer particles was proposed. The nucleation mechanism is considered to be thecoagulation of the precursor particles by homogeneous nucleation when the primary particles reach a critical size with highsurface charge density and sufficient stability. It had been proved by a special experiment that the early latex particles formedby the coagulation were stable. The primary particles grow by absorbing monomers and radicals in the polymerization systemand then become colloidally unstable again due to the understandable decrease of particle surface charge density, which leadsto the aggregation of the growing particles and the formation of larger latex pedicles therefrom. Aner the nucleation period,the preferential aggregation of the smaller particles in the propagation process leads to the change of the particles towards auniform size and narrower particle size distribution. The coexistence and competition of homogeneous nucleation,coagulation, propagation and aggregation result in the increase of the polydispersity index (U = D_(43)/D_(10)) in the first Stage,then its decrease in the later stage because of the competition of propagation and aggregation, and the gradual formation ofthe monodisperse particles.     

Nucleation in Emulsion Polymerization: Another Step towards Non-Micellar Nucleation Theory

Summary : Comprehensive experimental results of the nucleation stage of styrene emulsion polymerization in the absence as well as in the presence of emulsifier at different concentrations are presented. In addition, the influence of initiator type and presence of seed particles are studied. The nucleation mechanism is verified by means of on-line monitoring of the optical transmission and the conductivity of the aqueous phase. Results prove that micelles do not alter the nucleation mechanism which comprises the initiation of water soluble oligomers in the aqueous phase followed by their aggregation into colloidally stable latex particles. Surfactants assist with nucleation as they lower the activation free energy of particle formation. Contrary, in the presence of seed particles above a critical volume fraction the formation of new particles can be suppressed.     

A kinetic investigation of surfactant‐free emulsion polymerization of styrene using laponite clay platelets as stabilizers

We report the kinetics and mechanism of soap‐free emulsion polymerization of styrene using laponite platelets as stabilizers. The polymerization was initiated by potassium persulfate and the latex particles were stabilized by laponite platelets dispersed in water. Laponite adsorption on the polymer particles was enhanced by the addition of poly(ethylene glycol) monomethylether methacrylate (PEGMA). Particle nucleation can be described using the classical homogeneous nucleation mechanism followed by coagulation of unstable precursors. Oligomeric radicals formed in the water phase become insoluble and precipitate on the laponite surface leading to primary precursor particles composed of a few polymer chains and one or several clay platelets. Mature latex particles are then generated by coagulation and growth of the previously formed precursor particles. Both the nucleation and initial aggregation rates increased in the presence of PEGMA. Calorimetric monitoring of the polymerization allowed estimating the heat produced by the reaction and the monomer conversion. Hence, using the monomer material balance, the number of radicals in the polymer particles could be estimated precisely. The average number of radicals per particle, $ \bar n $ , was found to be high in the range 3–6. This result was attributed to strong attractive interactions between the growing radicals and the clay surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Crosslinked polystyrene latexes prepared with 12-(o-styryloxy)dodecyltrimethylammonium bromide

Crosslinked polystyrene latexes with high surface charge densities have been prepared with 1, 3, and 5 mol% divinylbenzene and 0.5–5.0 mol% of 12-(o-styryloxy)dodecyltrimethylammonium bromide ( 1 ). Within experimental error all of surfactant 1 was incorporated into the particles. Analysis of the latex particles by transmission electron microscopy showed nonspherical shapes, aggregates, and number average diameters ranging from 22 to 95 nm. The particle size decreases and the polydispersity increases with increasing amounts of surfactant 1 and of divinylbenzene in the monomer mixture. A mechanism is proposed for particle formation by precipitation of crosslinked polymer from monomer droplets to form primary particles, coagulation of the primary particles to colloidally stable aggregates, and growth by further polymerization.     

Particle nucleation and monomer partitioning in styrene O/W microemulsion polymerization

Particle nucleation in the polymerization of styrene microemulsions was found to take place throughout the polymerization as indicated by measurements of the particle number as a function of conversion. A mechanism based on the nucleation in the microemulsion droplets was proposed to explain the experimental findings although homogeneous nucleation and coagulation during polymerization were not completely ruled out. A thermodynamic model was developed to simulate the partitioning of monomer in the different phases during polymerization. The model predicts that the oil cores of the microemulsion droplets were depleted early in the polymerization (4% conversion). Due to the high monomer/polymer swelling ratio of the polymer particles, most of the monomer resides in the polymer particles during polymerization. The termination of chain growth inside the polymer particles was attributed to the chain transfer reaction to monomer. The low n? (less than 0.5) of the microemulsion system was attributed to the fast exit of monomeric radicals.     

MMA/BA/聚乙二醇马来酸单酯钠盐无皂乳液聚合的成粒机理

研究了在少量聚乙二醇马来酸单酯钠盐存在下,MMA/BA无皂乳液聚合成粒过程,发现聚合初期产生的初级粒子消失后,两次周期性地产生小粒子。经分析,是新的成核作用产生的,表明在聚合的中晚期,成核过程并未真正结束,而是处于成核-聚并的动态平衡之中。     

The mechanisms of latex particle formation and growth in the emulsion polymerization of styrene using the surfactant sodium dodecyl sulfate

A new method is presented that provides experimental information which is qualitatively and quantitatively sensitive to assumptions made as to the mechanisms of free radical entry and of latex particle formation in emulsion polymerization systems. The method consists of (1) obtaining (by electron microscopy) the full particle-size distributions (PSDs) at several different times soon after the cessation of latex particle nucleation, (2) using these PSDs to determine the volume dependences of the various rate coefficients governing particle growth by fitting the data to the appropriate evolution equations, and (3) employing these empirical rate coefficients to find that time dependence of the nucleation rate which fits the early-time PSD (again using the evolution equations). This method is quite sensitive to mechanistic assumptions: for example, one is able to determine whether or not the nucleation rate is an increasing or decreasing function of time. The technique is applied to a styrene nucleation system employing sodium dodecyl sulfate as surfactant at well above the critical micelle conventration. The data cannot be fitted even qualitatively by a simple one-step nucleation mechanis, whether it involes micellar entry or homogeneous nucleation. It is found, on the other hand, that the results can be accurately fitted by assuming that coagulation events between primary colloidal particles, perhaps formed by homogeneous nucleation, dominate both the nucleation process and the entry of free radicals into mature latex particles. In addition, the data indicate that the rate of free radical entry into the latex particles decreases with increasing particle size, at least for particles of unswollen radius less than ca. 40 nm.