Kinetic treatment of slow initiation in living carbocationic polymerization and investigation of benzyl halides as initiators for the polymerization of isobutylene

摘要

In contrast to earlier conclusions it is demonstrated that kinetic analysis of incremental monomer addition (IMA) experiments for living carbocationic polymerizations with slow initiation leads only to the ratio of apparent rate constants of initiation and propagation. The apparent rate constants depend on the true (bimolecular) rate constants and on the positions of the equilibria between dormant and active states of initiator and polymer chain ends, respectively. The same considerations are true for other living processes involving dormant species, e.g., group transfer polymerization or controlled radical polymerization. Slow initiation of living carbocationic polymerization of isobutylene (IB) was found with benzyl halide initiators, such as 4-methylbenzyl bromide, 4-methylbenzyl chloride, and 2,4,6-trimethylbenzyl chloride (TMBC), in conjunction with TiCl4 as co-initiator in the presence of N,N-dimethylacetamide in 40:60 v/v CH2Cl2/hexane solvent mixture at -78 degrees C. The obtained ratio of apparent rate constant of initiation and propagation is compared to other initiators. TMBC led to a new asymmetric telechelic polyisobutylene (PIB) with tertiary chlorine and 2,4,6-trimethylbenzyl end groups, which can be further derivatized. [References: 37]