链转移剂单体存在下苯乙烯乳液聚合反应研究

Studies on the Radical Emulsion Polymerization of Styrene in the Presence of Chain Transfer Monomer

以α-甲基丙烯酸-3-巯基己酯（MHM）为链转移剂单体，过硫酸钾（KPS）为引发剂，十二烷基苯磺酸钠（LAS）为乳化剂，通过乳液聚合合成支化聚苯乙烯（BPSt）．采用。H—NMR和三检测体积排除色谱（TD-SEC）对聚合反应过程和合成的聚合物进行了表征分析．结果表明，在合适的乳化剂用量、引发剂用量和聚合反应温度等条件下，反应初期生成的初级链可以完全转化成支化聚合物，在高单体转化率下不发生交联得到较窄分子量分布的高分子量支化聚苯乙烯（Mn,SEC〉1．4×10^5,Mw,malls〉2．0×10^6PDI〈4．5），而且所得聚合物表现出很高的支化程度（g’=0．5～0．6）．

Radical emulsion polymerization in the presence of 3-mercapto hexyl methacrylate （MHM） as the chain transfer monomer has been carried out in this study. Potassium persulfate was used as the initiator, and sodium dodecyl benzene sulfate was used as the emulsifier. The obtained polymers were characterized using 1H- NMR and triple-detection size exclusion chromatography. The primary chain length and the average MHM content per primary chain can be adjusted by the polymerization parameters. At the same feed ratio of monomer/branching agent,the molecular weight of the primary chain and its average MHM content will be increased with increase of emulsifier concentration and decrease of polymerization temperature or initiator concentration, which is beneficial to preparing branched vinyl polymers with high molecular weights and relatively narrow polydispersities because of high conversion of the primary chain into branched molecules. Excess high emulsifier concentration, low polymerization temperature or low initiator concentration will result in gelation because of excess coupling reaction between branched molecules. Compared with results reported in the literature, branched polymers with considerably higher molecular weights and relatively narrower polydispersities have been obtained without gelation at high monomer conversions because no primary chains remain.