乳液聚合成核阶段的模拟与分析

Simualtion and Analysis of Nucleation Stage for Emulsion Polymerization

建立了乳液聚合成核阶段的Monte Carlo模型,并用计算机对一个体积为10-17m3的微型反应器中苯乙烯的乳液聚合进行了模拟。以计算机生成随机数作为自由基被胶束和乳胶粒捕获的几率,模拟了在微型反应器中每一个自由基的生成、被胶束或乳胶粒捕获的过程以及每一个乳胶粒的生成及增长过程。通过对每一个乳胶粒在增长过程中各参数的统计计算,研究了乳液聚合成核阶段诸参数(乳胶粒数目、乳胶粒直径与粒径分布、单体转化率、聚合反应速率等)与乳化剂浓度[S]及引发剂浓度[I]的关系。结果表明,苯乙烯的乳液聚合体系中乳胶粒数目与[S]0.5996[I]0.4016成正比;在成核阶段乳胶粒直径分布先变宽后变窄,乳液聚合过程中乳胶粒直径分布有自动变窄的趋势;成核阶段持续时间t12与[S]0.60[I]-0.60成正比,成核阶段结束时的单体转化率x12与[S]1.20[I]-0.20成正比。

A Monte Carlo model of the nucleation stage for emulsion polymerization was established and the emulsion polymerization of styrene in a minireactor of 10-17 m3 was simulated with personal computer. Random numbers were arisen and set to be the probabilities of radicals entering both micelles and subsistent latex particles. The processes of the each single radical formation, capture of the radical by micelles or particles and the growth of each single particle in the minireactor were simulated. The evolutions of the various emulsion polymerization parameters in the whole nucleation stage were recorded and analyzed in detail. The effects of initiator concentration [I] and emulsifier concentration [S] on the parameters such as the latex particles number Np, average particle diameter and particle size distribution (PSD), monomer conversion and polymerization rate were predicted and studied. The results show that Np is in proportion to [S]0.5996[I]0.4016 for styrene emulsion polymerization, PSD becomes broader at first and then becomes narrower, and PSD tends to become narrower automatically during emulsion polymerization. The simulation results also show that the period of nucleation stage t12 is in proportion to [S]0.60 but in inverse proportion to [I]0.60, and the monomer conversion at the end of nucleation stage x12 is in proportion to [S]1.20 but in inverse proportion to [I]0.20.