Living carbocationic copolymerization of isobutylene with styrene

The carbocationic copolymerization of isobutylene (IB) and styrene (St), initiated by 2-chloro-2,4,4-trimethylpentane/TiCl4 in 60/40 (v/v) methyl chloride/hexane at -90 degrees C, was investigated. At a low total concentration (0.5 mol/L), slow initiation and rapid monomer conversion were observed. At a high total comonomer concentration (3 mol/L), living conditions (a linear semilogarithmic rate and M-n-conversion plots) were found, provided that the St concentration was above a critical value ([St](0) similar to 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching M-w/M-n similar to 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with M-n = 82,000 g/mol, the highest molecular weight ever achieved in carbocationic St polymerization. An analysis of this system by both the traditional gravimetric-NMR copolymer composition method and FTIR demonstrated penultimate effects. 113 enrichment was found in the copolymers at all feed compositions, with very little drift at a high total concentration and above the critical St concentration. (c) 2007 Wiley Periodicals, Inc.