Synthesis of Crystalline Syndiotactic Polystyrene Containing Vinyl Groups and Its Functionalization

Crystalline syndiotactic polystyrenes (sPS) containing a high content of vinyl functional groups are of fundamental interest and practical importance, which can promote the synthesis and research of various high-performance functional sPS, but their synthesis has remained highly challenging and rarely reported. Herein, we report the highly syndioselectivity polymerization of a series of ortho-alkoxystyrenes (StO) containing side-chain vinyl groups and the copolymerization with styrene (St) catalyzed by an yttrium alkyl complex. We have found that the distance between the vinyl group and the oxygen atom on StO can significantly influence the homopolymerization activity and stereoselectivity. Through this discovery, we have successfully synthesized sPS (rrrr > 99%) containing a vinyl side chains with melting temperatures (Tm) in the range of 148.1–152.0 °C. In addition, oxygen atoms on StO improve the polymerization activity and promote the St/StO copolymerization to form blocky copolymers, which is beneficial to maintaining the Tm at high vinyl group content (vinyl content: 5–50%, Tm: 256.6–261.0 °C). The excellent postfunctional properties of the obtained sPS containing vinyl groups have been confirmed by introducing hydroxyl groups and boronate ester groups through thiol–ene click chemistry, resulting in the formation of hydroxylated sPS or dynamically cross-linked sPS. We hope that our findings can guide the synthesis of various functional sPS to meet special application needs.