Carbocationic synthesis and characterization of polyolefins with Si-H and Si-Cl head groups

Abstract

The objective of this research was to review and examine the preparation of macroreagents consisting of polyolefins carrying Si-Cl or Si-H termini. These polymers were thought to combine the desirable physical-mechanical properties offered by these polyhydrocarbons with the chemical versatility of Si-Cl and Si-H bonds. A general synthetic method has been developed for the preparation of polyolefin macroreagents with silane head groups. The key to the synthesis was the finding that initiators containing Si-Cl or Si-H groups and a cationogenic moiety are able to induce transferless cationic polymerizations under conditions such that the silicon-functional groups survive. Extensive model experiments provided guidance for subsequent polymerizations. Experimental conditions have been worked out under which none of the electrophilic species (i.e., initiating and propagating carbenium ion) that arise during polymerization would destroy the Si-H function. Isobutylene and α-methylstyrene polymerizations were carried out under transferless conditions and the effect of solvent polarity, temperature, and monomer and initiator concentrations on polymerization details and product characteristics have been determined. Quantitative H¹ NMR and IR studies demonstrate the survival of the Si-H function during polymerization and the syntheses of polysiobutylene and poly(α-methylstyrene) carrying 1 Si-H terminus per chain. These macroreagents may be of great interest for the addition of polyolefin sequences to small molecules for purposes of modification or to polymers for the preparation of block and graft copolymers.