Synthesis of long-chain branched isotactic-rich polystyrene via cationic polymerization

Cationic polymerization of styrene was conducted with 1-chloro-1-phenylethane (SCl)/AlCl₃/phenyl methyl ether (PME) initiating system in hexane/CH₂Cl₂ (60/40, v/v) at ?80 °C. The kinetics for cationic polymerization of styrene was investigated by in-situ ATR-FTIR spectroscopy. The isotactic-rich polystyrene (iPS) with m dyad of 81%, mm triad of 63% and mmmm pentad of 50% could be synthesized. Small amounts of crystalline regions in iPS formed after flow-induced crystallization and the crystallinity increased with increasing the molecular weight of iPS. Furthermore, the long-chain branched isotactic-rich polystyrene (biPS) with around 12 times higher molecular weight than that of corresponding iPS could be synthesized via cationic polymerization of styrene by introducing a small amount of isoprene (Ip) as a comonomer and branching sites as well. The possible mechanism for long-chain branching formation via intermolecular alkylation reaction by using Ip structural units along polymer chain as branching sites was proposed. The nucleation rate of biPS could be greatly enhanced with increasing the content of branching sites, leading to an obvious increase in crystallinity. The multi-melting temperatures from 140 °C to 237 °C were observed in DSC curves of these PS products. The tensile strength of commercial atactic polystyrene could be improved remarkably from 41.4 MPa to 55.7 MPa by adding 16.7% of biPS.