硅氧烷的微乳液聚合动力学

Kinetics of microemulsion polymerization of octamethylcyclotetrasiloxane

在八甲基环四硅氧烷(D4)为单体,十二烷基苯磺酸(DBSA)为乳化剂和催化剂,正戊醇(C5H11OH)为助乳化剂的单体微乳液体系中,进行D4的微乳液聚合.研究了聚合温度、乳化体系组成、交联剂乙烯基三甲氧基硅烷(VTMS)对D4微乳液聚合动力学的影响.结果表明微乳液聚合没有常规乳液聚合的恒速反应期,在较高温度下,反应迅速进入快速反应阶段,达到一定转化率后又快速下降并趋于平衡转化率.高温有利于加快聚合速率.适当增大乳化剂DBSA与助乳化剂的比例,单体微滴的尺寸减小,聚合速率增大,产物粒径减小.交联剂VTMS的引入,不仅使线性聚硅氧烷形成交联的弹性体网络,而且改变了端羟基硅氧烷的缩合平衡反应速率,抑制了逆反应,加快了聚合速率.

The kinetics of octamethylcyclotetrasiloxane ring-opening polymerization in microemulsion with pentanol as co-emulsifier and dodecylbenzene sulfonic acid as emulsifier as well as catalyst were studied. The effects of reaction temperature, ratio of emulsifier-to-coemulsifier and introducing crosslink agent VTMS on polymerization rate were investigated in detail. The results showed that microemulsion polymerization did not have any constant reaction rate period as was observed in conventional emulsion polymerization. The polymerization reaction rate increased immediately, entering a fast reaction stage then decreased quickly after reaching a certain conversion, and finally approached equilibrium conversion. A higher temperature was favorable to speeding up polymerization. The size of initial monomer drops became smaller with increasing ratio of emulsifier-to-coemulsifier. This speeded up polymerization and decreased the size of polymer latex particles. Introducing crosslink agent VTMS could change linear polysiloxane into crosslinked elastic network and influence the equilibrium of the condensation reaction of end-hydroxyl polysiloxane by inhibiting inverse reaction. The polymerization was speeded up as well.