New telechelic polymers and sequential copolymers by polyfunctional initiator‐transfer agents (inifers). XIII. Influence of lewis acid strength and counteranion stability on the synthesis of telechelic polyisobutylenes

Abstract

SynopsisEfforts have been made to prepare perfect terminally functional linear telechelic polyisobutylenes with various Lewis acid coinitiators, BCl3, mcl3, TiC4, SnCL, VCL, and SbC15. However, the expected desirable results (F,, = 2.0, n,,,m,, = 1.5) were obtained only with BCh. Moreover, the concentration of BCl3 affects the molecular weight of telechelic polyisobutylenes prepared by the inifer technique. The Kennedy3mith inifer mechanism is insufficient to explain these observations. Extending this model by the concept of counteranion stability, of Heublein et d.,5 and assuming the participation of free ions and ion pairs in propagation and termination, led to a satisfactory mechanistic model. The exceptional utility of the BCl@CQ system is due to the high Lewis acid strength of BC4 and low counteranion stability of BClf. tionality (Fn = 2.0) and molecular weight dispersity (Mumn = 1.9, whereas *