Copolymerization of styrene with methyl-substituted styrenes in the presence of titanium monometallocenes

This paper investigates the homo- and copolymerization of styrene with p-methylstyrene, m-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene and 2,4,6-trimethylstyrene using a Cp*TiCl3 (Cp: cyclopentadienyl) semimetallocene catalyst activated with methylaluminoxane. Syndiotactic homo- and copolymers were obtained only for the monosubstituted monomers. For the di- or trisubstituted monomers, reduced reactivities, stereoregularities, and degrees of polymerization were obtained with respect to the monosubstituted monomers. More specifically, the homopolymerization of 2,5-dimethylstyrene and 2,4,6-trimethylstyrene and their copolymerization with styrene was inhibited. The reason for this are combined steric and inductive effects. The presence of methyl groups in para position seems to inhibit crystallization of the syndiotactic polymers. In contrast, crystallinity was evidenced in the materials produced in the presence of m-methyl substituted monomers.