Polymerization of isobutylene initiated with the system 2,5-dichloro-2,5-dimethylhexane/SnCl₄

Summary

The polymerizations of isobutylene in dichloromethane at-20°C initiated with the system 2,5-dichloro-2,5-dimethylhexane (DDH)/SnCl₄ were investigated. The polyisobutylene (PIB) samples obtained were examined by GPC and their molecular weight distribution curves were determined. It was found that PIB products obtained by the conventional procedure have a bimodal MWD and the weight content of the lower-molecular weight fraction increases with increasing concentration of DDH in the polymerization feed. The effect of ageing of DDH/SnCl₄ mixtures prepared in advance on MWD of the PIB samples was also proved. The results achieved lead to a conclusion that the ageing of the initiation system consists probably in the formation of the complex DDH-SnCl₄-H₂O, which protogenically again initiates the oligomerization of isobutylene, giving rise to oils with a narrow MWD, the polydispersity index ${{\bar M_{_w } } \mathord{\left/ {\vphantom {{\bar M_{_w } } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} \leqslant 1.3$. The possible role of the coordination polymerization mechanism is discussed.