Polyisobutylene-Based Thermoplastic Elastomers. 5. Poly(styrene-b-isobutylene-b-styrene) Triblock Copolymers by Coupling of Living Poly(styrene-b-isobutylene) Diblock Copolymers

Poly(styrene-b-isobutylene-b-styrene) (PSt-PIB-PSt) triblock copolymers have been prepared for the first time via coupling of living PSt-PIB diblock copolymers in a one-pot procedure. The PSt-PIB diblock copolymer was synthesized by living sequential cationic polymerization in methylcyclohexane (MeChx)/methyl chloride (MeCl) or hexane (Hex)/MeCl solvent mixtures at -80 degrees C using TiCl4 as co-initiator. It was found that, due to decomposition of the living PSt ends, the crossover efficiency (C-eff) from living PSt to IB decreases precipitously with time at close to 100% St conversion. To obtain high C-eff, IB must therefore be added at less than or equal to 95% St conversion. It was also found that in the presence of unreacted St the rate of IB block copolymerization decreases with time; this was attributed to the formation of relatively unreactive -St-IB-Cl ends. Due to the relatively high, concentration of these ends, coupling of living PSt-PIB was slow and incomplete. The obtained PSt-PIB-PSt triblock copolymers exhibited reasonable but significantly lower tensile strength (16-20 MPa) than that (23-25 MPa) reported for model PSt-PIB-PSt triblock copolymers of similar composition.