MMA/BA半连续乳液共聚的成核机理

Nucleation mechanism of MMA/BA semi-continuous emulsion copolymerization

在半连续乳液聚合过程中,研究了甲基丙烯酸甲酯(MMA)与丙烯酸丁酯(BA)共聚时单体配比及pH调节剂(NaHCO3)对成核过程的影响,并根据整个聚合过程中粒径及其分布的变化规律来推断体系的成核机理。实验结果表明:MMA摩尔分率fMMA不同时体系的成核机理不同,fMMA增大时,成核时间t1,2逐渐减小,而成核结束时的乳胶粒子数Npmax逐渐增大(fMMA=0除外);当MMA/BA共聚(fMMA=0.5763)时,单体转化率随NaHCO3用量的增加而增大,t1,2却保持不变,表明体系中除胶束成核之外存在均相成核。整个聚合过程中乳胶粒径及其分布规律也进一步验证了在MMA/BA共聚体系中,胶束成核与均相成核共存,且t1,2=16 min。

In semi-continuous emulsion polymerization with methyl methacrylate （MMA） and butyl acrylate （BA） as the monomers, the influences of the ratio of MMA to MMA and the pH buffer （NaHCO3） on the nucleation process were investigated. The nucleation mechanism was deduced by analyzing the growth of particle size and its distribution during the polymerization process. Experiment results show that the nucleation mechanisms are determined by the molar fraction of MMA （fMMA）, when fMMA increases the reaction time of nucleation t1,2 decreases, but the number of emulsion particles Np^max increases at the end of nucleation except BA homogenous polymerization; when fMMA = 0. 5763, as the amount of NaHCO3 increases the conversion rate of the monomers increases, but tl,2 remains constant, 16 min, which indicates the coexistence of the＂micellar nucleation＂ and ＂homogenous nucleation＂ mechanisms. The coexistence of the two nucleation mechanisms can also be verified by the analysis of the particle size and distribution of the emulsions.