Synthesis and characterization of (star polystyrene)-block-(polyisoprene)-block-(star polystyrene) copolymers

A (star polystyrene)-block-(linear polyisoprene)-block-(star polystyrene) copolymer, (S)nI(S)n, was prepared. The star polystyrene was produced via anionic polymerization of polystyrene macromonomers each containing an unsaturated double bond (vinyl) at the chain end. This vinyl-terminated polystyrene macromonomer (SSTM) was obtained beforehand via the synthesis of a living polystyrene using alkyllithium and the termination with p-chloromethylstyrene (PCMS). The living site in the core of the star polystyrene enabled the construction of the succeeding polyisoprene block resulting in the living (star polystyrene)-block-(linear polyisoprene) copolymer, (S)nI. This living diblock copolymer was then coupled with 1,2-dibromoethane (DBE) to form the well-defined (S)nI(S)n. Compared to a linear polystyrene-block-polyisoprene-block-polystyrene, SIS, with the same molecular weight, (S)nI(S)n had a higher Tg and exhibited a lamellae-forming phase separation in conjunction with many dislocation defects. The thermal stability appeared independent of the molecular structure, and the radius of gyration and viscosity of (S)nI(S)n were much smaller than SIS.