苯乙烯可逆加成-断裂链转移聚合动力学

为了实现可逆加成-断裂链转移(RAFT)聚合过程中,苯乙烯均聚、高分子量聚苯乙烯的合成及苯乙烯与其他单体共聚时,对苯乙烯转化率、共聚时组成和分子量大小的控制,进行了二硫代苯乙酸-1-苯基乙酯(PEPDTA)调控苯乙烯本体和细乳液聚合动力学分析。在本体聚合中,反应速率慢,链增长自由基与"中间态"自由基的终止反应对聚合速率影响较小,很难合成窄分布、高转化率、高分子量的聚苯乙烯;在细乳液聚合中,反应速率快、转化率高,随着PEPDTA含量增加,乳胶粒数量减少、粒径分布变宽,诱导期和缓聚现象明显;聚合物的数均分子量随转化率线性增长,RAFT试剂浓度越高,分子量分布越窄,反应时间越长,分布越宽。以Smith-Ewart方程为基础,建立了苯乙烯RAFT细乳液聚合动力学模型,模型动力学曲线与实验数据相符合,能较好地预测实验过程。

Kinetics of styrene reversible addition-fragmentation chain transfer polymerization

In order to control styrene composition and block molecular weight,styrene reversible addition-fragmentation chain transfer(RAFT),bulk and mini-emulsion polymerization processes were performed with 1-phenylethyl phenyldithioacetate(PEPDTA)during styrene homopolymerization and copolymerization with other monomers.For styrene bulk RAFT polymerization,retardation was not important because the cross-termination rate of propagating radical with intermediate radical was much slower than the termination rate of double propagating radicals.It was difficult to obtain high conversion and molecular weight with narrow polydispersity index(PDI)due to its slow reaction rate.For styrene mini-emulsion RAFT polymerization,the induction period and retardation were more obvious with increasing PEPDTA concentration,and the polymerization rate was much faster.Meanwhile,the number of particles decreased and its distribution became broader.The molecular weight increased linearly with increasing conversion,and its molecular weight distribution became much narrower when PEPDTA concentration increased.The theoretical modeling curves formulated were close to the experimental data,and RAFT mini-emulsion polymerization kinetics model based on the Smith-Ewart equation could well predict the experimental processes.