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 °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 ～ 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching M_w/M_n ～ 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. IB 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. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1778–1787, 2007