Random copolymer of styrene and diene derivatives via anionic living polymerization followed by intramolecular Friedel–Crafts cyclization for high-performance thermoplastics

A series of random copolymers of styrene and diene derivatives prepared by living anionic copolymerization, using tetrahydrofuran (THF) as a randomizer, were treated with various Brönsted and Lewis acids to cationically cyclize the adjacent diene–styrene units into tetrahydronaphthyl bicyclic main-chain structures via intramolecular Friedel–Crafts alkylation. This reaction produced high-performance plastics with a high glass transition temperature and robust mechanical properties. Of the various Friedel–Crafts catalysts, CF₃SO₃H and BF₃·2AcOH/benzyl chloride proved to be the most efficient in terms of their reactivity and product selectivity. All of the random styrene–diene-based copolymers, including styrene–isoprene (r-SIR), styrene–butadiene (r-SBR), p-methylstyrene–isoprene (r-pMSIR), and styrene–isoprene–butadiene (r-SIBR) copolymers, underwent efficient intramolecular cyclization by CF₃SO₃H despite the different monomer units and microstructures of the diene units, and yielded high-performance plastics (T_g ≥ 130 °C). The T_g value of the cyclized r-SBR was slightly lower than the T_g values observed for r-SIR and r-pMSIR. The cyclized random copolymers exhibited relatively high flexural moduli and more strength than the polystyrenehomopolymer. Thus, the styrene–diene-based random copolymer provides a novel platform for the production of high-performance thermoplastics that can be easily prepared from commercially available styrene and diene derivatives via living anionic polymerization followed by Friedel–Crafts alkylation.