Polyisobutylene‐containing block polymers by sequential monomer addition. X. Synthesis of poly(α‐methylstyrene‐b‐isobutylene‐b‐α‐methylstyrene) thermoplastic elastomers

Preparatory to triblock synthesis experiments, the cationic polymerization of α‐methylstyrene (αMeSt) was investigated using the 2‐chloro‐2,4,4‐trimethylpentane (TMPCI)/TiCl4 initiating system in the presence of triethylamine (Et3N) as electron donor (ED) and CH3Cl/n‐hexane mixed solvent in the −80 to −40°C range. Conversions are influenced by temperature, [TiCl4], [Et3N], and [αMeSt]. The polymerization of αMeSt is living at −80°C: Both termination and chain transfer to monomer are frozen out, however, initiation is slow relative to propagation. Highly syndiotactic (>94%) Pα Mest was obtained. At−60deg;C initiator efficiency is ca. 100%, but termination becomes evident. Et3N may act both as Ed and as proton scavenger. Novel poly(α‐methystyrene‐b‐isobutylene‐b‐α‐methylstyrene) (PαMeSt‐PIB‐PαMeSt) triblocks have been synthesized by adding αMeSt to biliving polyisobutylene carbocations (⊕PIB⊕) in the −80 to −40°C range. The effects of temperature, solvent polarity, and [Et3N] on the block copolymerization have been investigated. At −80°C, the rate of crossover from ⊕PIB⊕ to αMeSt is lower than that of propagation of PαMeSt⊕, so that the triblock is contaminated by PIB and PIB‐b‐PαMeSt. At −60°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).