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 Mn–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 Mw/Mn ∼ 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with Mn = 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

This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant (kp) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, kp = 1.35 × 104 L mol−1 s−1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded kp = 1.01 × 107 L mol−1 s−1, close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl4 from various laboratories yielded of ΔH ∼−25 and −34.5 kJ/mol for high and low TMPCl/TiCl4 ratios, respectively. Aromatic (cumyl‐type) initiators show ΔH ∼ −40 kJ/mol, whereas H2O/TiCl4 in the presence of the strong electron‐ pair donor dimethylacetamide gave ΔH = −12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005

Summary: Real-time FTIR is a powerful tool to obtain copolymerization reactivity ratios because it allows simultaneous monitoring of individual monomer consumption rates. Based on the Mayo-Lewis equation we showed that in reactivity ratios can be defined as the ratios of apparent rate constants of monomer consumption. The validity and limitations on this new method are discussed in the isobutylene-isoprene and isobutylene-styrene carbocationic copolymerization systems.