A NOVEL METHOD FOR THE DETERMINATION OF PROPAGATION RATE CONSTANTS - CARBOCATIONIC OLIGOMERIZATION OF ISOBUTYLENE

The tertiary carbenium ions 2(+) and 3(+), models of the propagating s pecies in carbocationic isobutylene polymerization, are generated from the tertiary chlorides 2c and 3c with a Lewis acid in the presence of isobutylene (1c) and one of the allylsilanes 1a or 1b, which act as t erminators, Since the rate of the termination reaction is known, the r atio of the telomerization products can be evaluated to give a propaga tion rate constant of (6 +/- 2) x 10(8) L mol(-1) s(-1) (independent o f temperature) for the carbocationic oligomerization of isobutylene in dichloromethane.