影响St-MMA-MA无皂乳液胶粒性质的因素 丙烯酸浓度及加料方式的影响

Effects of the Adding Methods of AA and its Concentration on the Properties of St-MMA-AA Soapless Latex Particles

以苯乙烯、甲基丙烯酸甲酯为主单体 ,丙烯酸为功能单体合成了三元无皂乳液共聚胶粒。用TEM观测了胶粒形态、大小及其分布 ;以电导滴定法测定了胶粒表面 -COOH的密度。考察了不同的聚合阶段加入不同量的丙烯酸对所得胶粒形态、大小及其表面 -COOH的密度的影响。结果表明 :在聚合前加入丙烯酸 ,随着丙烯酸浓度的增大 ,胶粒粒径减小、分散系数增大 ;在成核后期滴加丙烯酸 ,胶粒粒径较大且随丙烯酸浓度增大粒径变化不大而分散系数迅速增大 ;在聚合完成期滴加丙烯酸 ,胶粒粒径最大且在一定范围内随着丙烯酸浓度的增大 ,粒径和分散系数增大。不论丙烯酸以哪种方式加入 ,随着丙烯酸浓度的增大胶粒表面 -COOH密度增大 ;在相同丙烯酸浓度下 ,聚合完成期滴加丙烯酸所得胶粒表面 -COOH密度最大 ,聚合前加入丙烯酸所得胶粒表面 -COOH密度最小。

Latex particles were obtained by soapless emulsion copolymerization of styrene (St) and methyl methacrylate (MMA) in the presence of functional monomer acrylic acid (AA) . The morphology, size and size distribution of the latex particles were observed or surveyed by TEM, and the distribution of -COOH in the latex was determined by conductometric titration and the density of surface -COOH was computed. Effects of the concentration of AA and its feeding process at different polymerization stages on the size and size distribution, density of surface -COOH of the latex particles were investigated. The results show that the average diameter (D) decreases and its dispersion parameter (D p) increases with increasing [AA] if AA was added in one batch before polymerization. D is larger and slightly decreases, and D p increases significantly with increasing [AA] if AA was added dropwise at the latter of nucleation stage. D and D p increase with increasing [AA] if AA was added dropwise after the steady stage and [AA] is winth a certain range. The density of surface -COOH (D c) increases with increasing [AA] no matter how AA was added, and D c is the largest when AA was added dropwise after the steady stage and it is the least when AA is added in one batch before polymer ization.