Effect of the mixture t ‐ BuCl/SnCl₄ on the cationic polymerization of isobutylene

Abstract

The polymerizations of isobutylene initiated with the system tert‐butyl chloride (t‐BuCl)/SnCl4 and carried out in CH2Cl2 at −20°C and −78°C were investigated. The results obtained demonstrate that the presence of t‐BuCl in the polymerizing system gives rise to a PIB product with a distinctly bimodal MWD. The higher‐molecular weight (HMW) PIB, M̄n = 20000, I=M̄w/M̄n ∼ 2.5, is the result of existence of the protogenic initiation with residual water in the reaction system. The lower‐molecular weight (LMW) PIB, M̄n < 600, M̄w/M̄n ≤ 1.4, is the product of polymerization initiated presumably with a complex t‐BuCl‐SnCl4‐H2O. To elucidate the reaction mechanism of the polymerization initiated with the complex, a series of similar isobutylene polymerizations using the initiation system 2,5‐dichloro‐2,5‐dimethylhexane (DDH)/SnCl4 was run and the oily LMW PIB samples were investigated by 1H‐NMR. A new polymerization mechanism describing the role of DDH and t‐BuCl is suggested.