Polyisobutylene based thermoplastic elastomers: VI. Poly(alpha-methylstyrene-b-isobutylene-6-b-alpha-methylstyrene) triblock copolymers by coupling of living poly(alpha-methylstyrene-b-isobutylene) diblock copolymers

Poly(alpha-methylstyrene-b-isobutylene-b-alpha-methylstyrene) (P alpha MeSt -PIB-P alpha MePSt) triblock copolymers have been prepared via coupling of living diblock copolymers in a one pot procedure. The P alpha MeSt-PIB dibl ock copolymers were synthesized by living sequential cationic polymerizatio n in methylcyclohexane (MeChx)/methylchloride (MeCl) solvent mixtures at -8 0 degrees C using BCl3 for alpha MeSt polymerization and TiCl4 for IB polym erization as coinitiators. The crossover efficiency, however, was only simi lar to 57 %, due to intermolecular alkylation (indanyl ring formation) afte r the addition of TiCl4. By modifying the P alpha MeSt end with a short seg ment of p-chloro-alpha-methylstyrene before IB addition the crossover effic iency was increased to 90 %. Coupling of the living block copolymers with 2 ,2-bis[4-(1-phenylethenyl)phenyl]propane (BDPEP) was rapid and gave similar to 90 % efficiency.