Living Cationic Homopolymerization of Isobutyl Vinyl Ether and Sequential Block Copolymerization of Isobutylene with Isobutyl Vinyl Ether. Synthesis and Mechanistic Studies

Abstract

The living polymerization of isobutyl vinyl ether (IBVE) and sequential block copolymerization of isobutylene (IB) with IBVE have been achieved using TiCl 4 coinitiator in methyl chloride/ hexanes solvent mixtures in the -80 to -40 °C temperature range. Poly(IB-b-IBVE) with ∼100% blocking efficiency has been synthesized for the first time. Close to 100% initiator efficiencies as well as 100% crossover efficiencies were obtained with 2,4,4-trimethyl-2-chloro-pentane (TMPCI) and PIBCl, respectively. The procedure involved capping with 1,1-diphenylethylene, followed by the addition of nBu 4 NCl to reduce the concentration of free, uncomplexed TiCl 4 to [TiCl 4 ] free < [chain end] before the addition of IBVE. Mechanistic studies indicated that the presence of common ion salt is not necessary, and that living polymerization of IBVE and sequential block copolymerization of IB with IBVE can also be accomplished in its absence when [TiC 4 ] < [chain end]. It is proposed that under these conditions the gegenion is TiCl 5 - , a much stronger nucleophile compared to the Ti 2 Cl 9 - dimeric gegenion which dominates at [TiCl 4 ] free /[chain end] ≥ 2.