Abstract: By using maximum bubble pressure method (MBPM), the dynamic surface tension (DST)of styrene (St)and methyl methacrylate (MMA)surfactant-free emulsion copolymerization in aqueous solution of poly(ethylene glycol)(PEG)or without PEG was studied.It was observed that PEG could slow down copolymerization rate of the system.The conversion of the system was above 98% without PEG after reacting 50 minutes, approaching the end point, while, it was just 49% for the system with PEG.In the presence of PEG, the copolymer of St/MMA initiated by potassium persulphate could become a kind of material that had stronger surface activity.This kind of copolymer with lower surface tension was formed when the conversion was just 5%.Lower surface tension was the force that drove copolymer into particle pile to form small and stable particles, and gave the particles enough surface electric charge to escape from the particle pile eventually.

Key words: dynamic surface tension, styrene, methyl methacrylate, surfactant-free emulsion polymerization, poly(ethylene glycol)

摘要： 利用最大泡压法（MBPM）研究了苯乙烯（St）/甲基丙烯酸甲酯（MMA）在有、无聚乙二醇（PEG）水溶液中进行无皂乳液聚合过程中的动态表面张力变化。发现PEG使体系反应速率变慢，反应50 min，有PEG参与的体系转化率只有49%，而无PEG参与的体系转化率已达到98%以上，接近终点。St/MMA和引发剂形成的聚合物在PEG的作用下，形成了一种具有更强表面活性的聚合物，表面活性水平高于PEG以及无PEG参与聚合体系的聚合物，但弱于混合单体及齐聚物。这种较强表面活性的聚合物在转化率只有5%的时候就已经存在，是聚合物进入粒子堆形成稳定小粒子的动力，并最终使粒子带有足够脱离粒子堆的表面电荷。

关键词: 动态表面张力, 苯乙烯, 甲基丙烯酸甲酯, 无皂乳液聚合, 聚乙二醇