无皂乳液聚合制备亚微米级单分散聚苯乙烯微球

Preparation of monodisperse micron-size polystyrene particles by emulsifier-free emulsion polymerization

采用无皂乳液聚合法制备了具有单分散性的亚微米级聚苯乙烯微球 ,考察了聚合体系pH值、单体及引发剂用量对聚合转化率、微球粒径及其分布的影响。结果表明 ,采用NaOH和NaHCO3 复合溶液调节聚合体系pH值是控制聚合动力学、微球粒径及单分散性的有效手段 ,当其质量比为 1∶1时效果较好。随碱性复合溶液加入量的增加 ,最终转化率下降 ,微球粒径则由于复合溶液同时起到电解质的作用而存在极大值。随过硫酸钾 (KPS)质量分数的增加 ,反应前期聚合转化率增大 ,但其用量过大 ,会导致体系pH值偏低 ,KPS过早消耗完毕 ,故反应后期最终转化率偏低 ;其用量过低 ,会影响粒径的单分散性。当KPS质量分数为单体的 2 %～ 3%时 ,聚合体系稳定性增加并改善了微球的单分散性 ,粒径趋小。单体用量的变化对聚合速率影响不大 ,随单体质量分数的提高 ,微球最终粒径增大 ,当单体质量分数过高 ,会影响微球的单分散性乃至体系失稳 ,一般以不超过 10

The monodisperse micron-size polystyrene particles were prepared by emulsifier-free emulsion polymerization. The effects of pH value,styrene and potassium persulfate (KPS) content on conversion, particle size and its distribution were mainly investigated. The results showed that it was useful method for addition of both NaOH and NaHCO 3 mixed solvent to control polymerization kinetics, size and its monodispersity of obtained particles, which adjusted pH value change during polymerization process. It was better based on its monodispersity when the mass ratio of NaOH to NaHCO 3 was 1∶1. With increasing the basic mixture as both pH alleviant and electrolyte, final conversion decreased and maximum of particle size existed. Conversion increased with increasing KPS content at the early stage of polymerization process. However, the final conversion was lower when excessive KPS was added because the decomposition of persulfate was accelerated and initiator consume rapidly at lower pH value. Uniform and stable particles were obtained via advisable initiator content between 2% and 3% based on monomer. Moreover, the influence of limited change of monomer concentration on polymerization rate could be neglected. Particle size enlarged with higher solid content. However, unstability and broad distribution occured when monomer concentration tends to be higher over 10%.