亲核性调节剂在异丁烯阳离子聚合中的作用机理

Mechanistic Roles of Nucleophiles in the Carbocationic Polymerization of Isobutylene

亲核性调节剂在异丁烯活性阳离子聚合中发挥着极其重要的作用 ,其作用机理主要包括 :(1)碳阳离子稳定化作用 ,即亲核性试剂或它们与Lewis酸生成的络合物与增长链的末端结合 ,来降低活性中心阳离子的“阳离子性” ,抑制副反应 ,使聚合反应呈现活性聚合特征 ;(2 )质子捕获作用 ,即亲核性试剂捕获质子 ,抑制质子的不可控引发和链转移反应 ;(3)增长链表观稳定作用 ,即亲核试剂降低了增长速率与引发速率之比 ,提高引发效率 ,降低增长速率 ,降低分子量分布 ;(4)抑制自由离子增长作用 ,即亲核试剂与质子源和Lewis酸反应 ,生成同阴离子 ,产生同离子效应 ,抑制自由离子活性中心的引发增长作用。

The mechanistic roles of nucleophiles in living carbocationic polymerization of isobutylene were reviewed.There are 4 mechanisms:A.The “carbocation stabilization”—nucleophiles and/or their complexes with Lewis acid interact with the growing chain end to reduce its “cationicity” and the reduction in cationicity to decrease the polymerization rate,suppress chain transfer and termination reactions;B.The “proton-scavenging”— the removal of protic impurities by externally added nucleophiles and the elimination of “induced” chain transfer;C.The “apparent stabilization of the growing chain ends”— the reduction in the instantaneous carbocation concentration;D.The“suppression of free ions”— the common ions in situ production via the scavenging of protic impurities.