团聚纳米SiO_2在苯乙烯乳液聚合过程中的再分散过程及机理

用二氧化硅 (SiO2 )存在下的乳液聚合法制备了聚苯乙烯 (PSt) 纳米SiO2 复合材料 ,研究了苯乙烯(St)乳液聚合过程中团聚纳米SiO2 的解离与再分散过程及分散的机理 .发现商品纳米SiO2 粒子以团聚体形式存在 ,团聚体大小远超出纳米级范围 .随聚合时间的延长 ,St的转化率逐渐增加 ,而PSt SiO2 复合微胶囊的粒径逐渐减小 ,反应 12 0min后 ,转化率和复合微胶囊粒子的粒径趋于稳定 .透射电镜 (TEM)也显示PSt SiO2 复合微胶囊粒子具有海岛结构 ,而SiO2 粒子的粒径在纳米范围内 ,表明在乳液聚合过程中SiO2 团聚体被逐渐解离 ,并重新分散到纳米尺度 .红外光谱研究发现 ,在乳液聚合过程中 ,除生成PSt均聚物外 ,还在纳米SiO2 表面生成了PSt接枝共聚物 ,改善了无机纳米粒子与聚合物之间的界面相容性 .聚合过程中的反应热和剪切搅拌是团聚体被解离和重新分散的主要原因 ,而生成的聚合物起到隔离作用

MECHANISM AND PROCESS OF THE REDISPERSION OF THE AGGREGATED NANO-SiO2 PARTICLES DURING EMULSION POLYMERIZATION OF STYRENE

A polystyrene (PSt)/nano-SiO 2 nanocomposite was prepared through emulsion polymerization of styrene in the presence of SiO 2,and the mechanism and process of the redispersion of the aggregated nano-SiO 2 particles during emulsion polymerization were studied.It was found that the commercial nano-SiO 2 particles were usually in the state of aggregation according to TEM and SEM results,and their diameter was over the range of nanometer.With the increase of the polymerization time,the conversion of styrene gradually increased and the latex diameter of the PSt/SiO 2 microcapsule decreased.When the polymerization time reached 120 min,the conversion and the latex diameter tended to be constant.The TEM photograph also showed that the PSt/SiO 2 microcapsule had the sea-island structure and the size of SiO 2 particles was in the range of nanometer,which suggested that the aggregated nano-SiO 2 particles were gradually redispersed during emulsion polymerization.FTIR studies approved that in addition to the formation of homopolymer the grafted polystyrene had also been produced on the SiO 2 surface,which improved the interfacial compatibility between polystyrene and nano-SiO 2. The released heat during the polymerization and the shear force were the main reasons causing the redispersion of the aggregated nano-SiO 2.