A New Approach to Styrenic Thermoplastic Elastomers: Synthesis and Characterization of Crystalline Styrene−Butadiene−Styrene Triblock Copolymers†

Crystalline styrene−butadiene−styrene (SBS) triblock copolymers consisting of elastic cis-polybutadiene (cis-PB) chemically bonded with crystallizable syndiotactic polystyrene (syn-PS) were synthesized through a stereospecific sequential triblock copolymerization of S with B catalyzed by C5Me5TiMe3/B(C6F5)3/trioctylaluminum (Al(oct)3) under controllable polymerization conditions. The first polymerization step was conducted at −25 °C, yielding syn-PS with controllable molecular weight by changing the polymerization time. The second one was started with the addition of excess B to the progressing syn-PS polymerization at −40 °C, yielding syn-PS/cis-PB diblock copolymer with high block efficiencies. The third one was conducted at −25 °C just by removal of the unreacted B in order to enhance the reinsertion and propagation of the remained S, yielding crystalline SBS triblock copolymers with relatively high PS compositions. The livingness of the whole polymerization process was confirmed through a linear incre...