Polyisobutylene based thermoplastic elastomers: VI. Poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) triblock copolymers by coupling of living poly (α-methylstyrene-b-isobutylene) diblock copolymers

Summary Poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) (PαMeSt-PIB-PαMePSt) triblock copolymers have been prepared via coupling of living diblock copolymers in a one pot procedure. The PαMeSt-PIB diblock copolymers were synthesized by living sequential cationic polymerization in methylcyclohexane (MeChx)/methylchloride (MeCl) solvent mixtures at −80 °C using BCl₃ for αMeSt polymerization and TiCl₄ for IB polymerization as coinitiators. The crossover efficiency, however, was only ∼57 %, due to intermolecular alkylation (indanyl ring formation) after the addition of TiCl₄. By modifying the PαMeSt end with a short segment of p-chloro-α-methylstyrene before IB addition the crossover efficiency was increased to 90 %. Coupling of the living block copolymers with 2,2-bis4-(1-phenylethenyl)phenyl]propane (BDPEP) was rapid and gave ∼ 90 % efficiency. Received: 13 July 2000/Accepted: 3 August 2000