Electron pair donors in carbocationic polymerization

Abstract

Preparatory to a detailed presentation of a large body of accumulated information, representative data have been selected to demonstrate that well-defined narrow molecular weight distribution (MWD) (¯M_w/¯M_n ≅= 1.1) polyisobutylene (PIB) can be readily prepared in the M_n = 1000 – 100,000 range in the presence of certain types of electron pair donors (EDs) under a great variety of conditions. Specifically, many initiating systems, such as dicumyl chloride/BCl₃, dicumyl alcohol/BCl₃, 2-chloro-2,4,4-trimethylpentane/TiCl₄, that induce nonliving polymerizations and/or give relatively broad MWD PIBs, in the presence of suitable EDs, e.g., dimethyl sulfoxide (DMSO), dimethyl acetamide (DMA), give rise to living polymerizations and yield narrow MWD products. Evidently, by the use of select EDs various undesirable side reactions, i.e., uncontrolled initiation, chain transfer, irreversible termination, indanyl end-group formation, etc., that plague carbocationic polymerizations and which therefore yield ill-defined relatively broad MWD products, can be eliminated and well-defined narrow MWD products can be obtained. The addition of EDs to otherwise extremely rapid carbocationic polymerizations results in lower controlled rates. All these observations and beneficial effects can be explained by controlled carbocation stabilization by EDs, a subject that will be explored and discussed in detail in this series of publications.