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1.
MMA/BA无皂乳液聚合机理研究——三阶段成粒机理   总被引:3,自引:1,他引:2  
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  相似文献   

2.
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Coulter 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.  相似文献   

3.
无皂乳液聚合中单分散粒子的形成过程   总被引:17,自引:3,他引:14  
在少量双官能团水溶性共单体(磺化下二酸-聚乙二醇-烯丙基缩水甘油醚酯)存在下进行MMA/BA无皂乳液聚合,用CoulterLS230激光粒径分析仪研究了乳胶粒子的成核机理和单分散粒子的形成过程,乳胶粒子的成粒程属多步成粒机理,先均相成核,形成不稳定的初始粒子,然后凝聚成稳定乳胶粒,其粒径分布经历了先变宽后变窄的过程,这是聚合过程中成核-凝聚-增长共同作用,相互竞争的结果,它还导致聚合初期出现周期成  相似文献   

4.
MMA—St无皂乳液聚合成核机理探讨   总被引:5,自引:0,他引:5  
讨论了MMA-St无皂乳液聚合,当[KPS]=2.77×10~(-3)mol/L,[MMA]0.51mol/L,[St]=0.49mol/L,70℃反应5.0小时,能得到较高的聚合转化率,较小的胶乳粒径和较大的粒子浓度,并对不同反应时期聚合物的分子量及其分布进行了测定,认为该无皂乳液聚合体系为均相沉淀成核机理。当转化率大于30.9%时,胶乳粒的凝聚程度大于胶乳粒的生成速度。KPS分解产生的自由基起到了稳定乳液的作用。  相似文献   

5.
利用高倍光学显微镜、库尔特粒径测试仪、TEM及zeta电位跟踪观测了苯乙烯(St)与甲基丙烯酸甲酯(MMA)在聚乙二醇(PEG)水溶液无皂乳液共聚过程中的粒径、粒径分布以及zeta电位变化.聚合物粒径会经历由小到大(某些粒径甚至超过1000μm,分布在0.04~2000μm的极宽范围内),再由大变小(形成的数均分布在0.04~0.18μm)过程,且粒径分布也由宽变窄,最终粒径数均分布集中在0.04~0.18μm窄范围内.结合聚合转化率数据,根据PEG水溶液中进行的St/MMA无皂乳液共聚粒径变化过程,以及zeta电位在聚合过程中异于普通无皂乳液的现象,认为该体系在反应初期形成的粒子会形成粒子堆,并随着聚合反应的继续,带有离子片段的自由基链段不断扩散进入粒子堆表面的小粒子,使其zeta电位不断增强,最终脱离粒子堆.提出了PEG水溶液中St/MMA无皂乳液共聚聚并脱析成核机理.  相似文献   

6.
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  相似文献   

7.
MMA/BA/聚乙二醇马来酸单酯钠盐无皂乳液聚合的成粒机理   总被引:3,自引:0,他引:3  
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,发现聚合初期产生和初级粒子消失后,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。  相似文献   

8.
以偶氮二异丙基脒盐酸盐(V50)为引发剂,采用4-乙烯吡啶(4-VP)/丙烯酸丁酯(BA)为混合单体,分别以二乙烯苯(DVB)或双甲基丙烯酸乙二醇酯(EGDMA)为交联剂,用无皂乳液聚合的方法合成了一系列正电性共聚乳液,并用扫描电镜(SEM)、Zeta电位测定仪详细研究了单体配比、交联剂种类和交联度对粒径大小及其分布、粒子形态和乳液电性能的影响,并探讨了该三元无皂乳液聚合的成核机理。结果表明:4VP/BA的无皂乳液聚合遵循均相成核机理。当BA含量低或者微球交联度较小时,高分子亲水性强,临界链长度大,生成粒子数目少,所以粒径大;随着BA含量的增加或者交联度的增大,高分子疏水性增强,临界链长度沽小,生成粒子数目增多,粒径变小,当BA/4VP=1/4(g/g)时,得到单分散共聚乳胶,少量BA与4VP共聚可以明显提高乳液的稳定性。  相似文献   

9.
聚硅氧烷/丙烯酸酯核/壳复合胶乳的粒径分布与成核机理   总被引:12,自引:0,他引:12  
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 .  相似文献   

10.
醋酸乙烯酯-丙烯酸丁酯乳液聚合成核机理   总被引:7,自引:2,他引:5  
本工作研究了醋酸乙烯酯(VA)和丙烯酸丁酯(BA)乳液共聚合.通过对不同共聚单体配比下共聚合时胶乳粒径及胶粒数密度随转化率变化的分析,对VA/BA乳液共聚合成核及粒增长机理进行了探讨,指出水相成核是高VA含量时胶粒数密度较大的主要原因并解释了胶粒数密度及胶乳粒径与单体转化率的关系,同时也讨论了该共聚体系一步法聚合时反应机理与胶粒形态的关系.  相似文献   

11.
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.  相似文献   

12.
MMA/BA/双官能团单体无皂共聚乳液的稳定性   总被引:3,自引:0,他引:3  
用马来酸酐和乙二醇合成了一系列双官能团共单体,将其用于MMA/BA无皂乳液共聚合。研究了共单体的空间效应,用量,加料方式对其无皂乳液稳定性的影响。用适当的共单体和半连续加料方式,可得到较稳定的乳液,粒径分布接近单分散。凝聚物的生成机理主要是失稳凝聚和架桥凝聚。  相似文献   

13.
无乳化剂乳液聚合法合成单分散大粒径高分子微球的研究   总被引:16,自引:0,他引:16  
无乳化剂乳液聚合法合成单分散大粒径高分子微球的研究朱世雄杜金环金熹高陈柳生(中国科学院化学研究所北京100080)关键词无乳化剂乳液聚合,单分散,均相成核,低聚物胶束微米级大粒径单分散高分子微球在标准计量、情报信息、分析化学等许多领域都有广泛的...  相似文献   

14.
The principal subject discussed in the current paper is the radical polymerization in the aqueous emulsions of unsaturated monomers (styrene, alkyl (meth)acrylates, etc.) stabilized by non-ionic and ionic/non-ionic emulsifiers. The sterically and electrosterically stabilized emulsion polymerization is a classical method which allows to prepare polymer lattices with large particles and a narrow particle size distribution. In spite of the similarities between electrostatically and sterically stabilized emulsion polymerizations, there are large differences in the polymerization rate, particle size and nucleation mode due to varying solubility of emulsifiers in oil and water phases, micelle sizes and thickness of the interfacial layer at the particle surface. The well-known Smith-Ewart theory mostly applicable for ionic emulsifier, predicts that the number of particles nucleated is proportional to the concentration of emulsifier up to 0.6. The thin interfacial layer at the particle surface, the large surface area of relatively small polymer particles and high stability of small particles lead to rapid polymerization. In the sterically stabilized emulsion polymerization the reaction order is significantly above 0.6. This was ascribed to limited flocculation of polymer particles at low concentration of emulsifier, due to preferential location of emulsifier in the monomer phase. Polymerization in the large particles deviates from the zero-one approach but the pseudo-bulk kinetics can be operative. The thick interfacial layer can act as a barrier for entering radicals due to which the radical entry efficiency and also the rate of polymerization are depressed. The high oil-solubility of non-ionic emulsifier decreases the initial micellar amount of emulsifier available for particle nucleation, which induces non-stationary state polymerization. The continuous release of emulsifier from the monomer phase and dismantling of the non-micellar aggregates maintained a high level of free emulsifier for additional nucleation. In the mixed ionic/non-ionic emulsifiers, the released non-ionic emulsifier can displace the ionic emulsifier at the particle surface, which then takes part in additional nucleation. The non-stationary state polymerization can be induced by the addition of a small amount of ionic emulsifier or the incorporation of ionic groups onto the particle surface. Considering the ionic sites as no-adsorption sites, the equilibrium adsorption layer can be thought of as consisting of a uniform coverage with holes. The de-organization of the interfacial layer can be increased by interparticle interaction via extended PEO chains--a bridging flocculation mechanism. The low overall activation energy for the sterically stabilized emulsion polymerization resulted from a decreased barrier for entering radicals at high temperature and increased particle flocculation.  相似文献   

15.
The principal subject discussed in the current paper is the radical polymerization of styrene in the three- and four component microemulsions stabilized by a cationic emulsifier. Polymerization in the o/w microemulsion is a new polymerization technique which allows to prepare the polymer latexes with the very high particle interface area and narrow particle size distribution. Polymers formed are very large with a very broad molecular weight distribution. In emulsion and microemulsion polymerizations, the reaction takes place in a large number of isolated loci dispersed in the continuous aqueous phase. However, in spite of the similarities between emulsion and microemulsion polymerization, there are large differences caused by the much larger amount of emulsifier in the latter process. In the emulsion polymerization there are three rate intervals. In the microemulsion polymerization only two reaction rate intervals are commonly detected: first, the polymerization rate increases rapidly with the reaction time and then decreases steadily. Essential features of microemulsion polymerization are as follows: (1) polymerization proceeds under non-stationary state conditions; (2) size and particle concentration increases throughout the course of polymerization; (3) chain-transfer to monomer/exit of transferred monomeric radical/radical re-entry events are operative; and (4) molecular weight is independent of conversion and distribution of resulting polymer is very broad. The number of microdroplets or monomer-starved micelles at higher conversion is high and they persist throughout the reaction. The high emulsifier/water ratio ensures that the emulsifier is undissociated and can penetrate into the microdroplets. The presence of a large amount of emulsifier strongly influences the reaction kinetics and the particle nucleation. The mixed mode particle nucleation is assumed to govern the polymerization process. At low emulsifier concentration the micellar nucleation is dominant while at a high emulsifier concentration the interaction-like homogeneous nucleation is operative. Furthermore, the paper is focused on the initiation and nucleation mechanisms, location of initiation locus, and growth and deactivation of latex particles. Furthermore, the relationship between kinetic and molecular weight parameters of the microemulsion polymerization process and colloidal (water/particle interface) parameters is discussed. In particular, we follow the effect of initiator and emulsifier type and concentration on the polymerization process. Besides, the effects of monomer concentration and additives are also evaluated.  相似文献   

16.
A general kinetic model of particle formation in an ultrasonically initiated emulsion polymerization system is presented. This model takes into account homogeneous, micelle entry, and monomer droplet nucleation mechanism. The effects of the ultrasound in producing free radical, degrading free radical and influencing the fashion of the nucleation are also considered. Moreover, chain transfer to monomer and termination in the aqueous phase, capture of oligomer radicals by particles, and coagulation of particles are also considered. An analytical solution is obtained for the initial particle stage consideration. This model predicts that, if the desorption of radical from particles can be neglected, the concentration of the total radical in the aqueous phase is directly proportional to the cavitation concentration. Model predictions are in good agreement with experimental data obtained from the literature.  相似文献   

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