LIVING CARBOCATIONIC POLYMERIZATION .58. POLYISOBUTYLENE-CONTAINING BLOCK POLYMERS BY SEQUENTIAL MONOMER ADDITION .10. SYNTHESIS OF POLY(ALPHA-METHYLSTYRENE-B-ISOBUTYLENE-B-ALPHA-METHYLSTYRENE) THERMOPLASTIC ELASTOMERS

Preparatory to triblock synthesis experiments, the cationic polymerization of alpha-methyl-styrene (alphaMeSt) was investigated using the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4 initiating system in the presence of triethylamine (Et3N) as electron donor (ED) and CH3Cl/n-hexane mixed solvent in the -80 to -40-degrees-C range. Conversions are influenced by temperature, [TiCl4], [Et3N], and [alphaMeSt]. The polymerization of alphaMeSt is living at -80-degrees-C: Both termination and chain transfer to monomer are frozen out, however, initiation is slow relative to propagation. Highly syndiotactic (>94%) PalphaMest was obtained. At -60-degrees-C initiator efficiency is ca. 100%, but termination becomes evident. Et3N may act both as ED and as proton scavenger. Novel poly(alpha-methystyrene-b-isobutylene-b-alpha-methylstyrene) (PalphaMeSt-PIB-PalphaMeSt) triblocks have been synthesized by adding alphaMeSt to biliving polyisobutylene carbocations (+PIB+) in the -80 to -40-degrees-C range. The effects of temperature, solvent polarity, and [Et3N] on the block copolymerization have been investigated. At -80-degrees-C, the rate of crossover from +PIB+ to alphaMeSt is lower than that of propagation of PalphaMeSt+, so that the triblock is contaminated by PIB and PIB-b-PalphaMeSt. At -60-degrees-C, crossover occurs preferentially. The rate of propagation relative to that of crossover is also reduced by lowering the solvent polarity and increasing the [Et3N]. High crossover efficiency and blocking efficiency can be obtained under optimum blocking conditions. The triblocks are novel thermoplastic elastomers (TPEs). C 1994 John Wiley & Sons, Inc.