Copolymerization of styrene and conjugated dienes with half-sandwich titanium(IV) catalysts: The effect of the ligand structure on the monomer reactivity, monomer sequence distribution, and insertion mode of dienes

The copolymerization of styrene and 1,3-butadiene (Bd) or isoprene (Ip) was carried out with half-sandwich titanium(IV) Cp′TiCl₃ catalysts (where Cp′ is cyclopentadienyl 1, indenyl 2, or pentamethylcyclopentadienyl 3) with methylaluminoxane as a cocatalyst. For the copolymerization with Bd, catalyst 3 gave the copolymers containing the highest amount of Bd among the catalysts used. The resulting copolymers were composed of a styrene-Bd multiblock sequence. High melting points were observed in the copolymers prepared with catalyst 1. The structures of hydrogenated poly(styrene-co-Bd) were studied by ₁₃C NMR spectroscopy, and the long styrene sequence length was detected in the copolymers prepared with catalyst 1. For styrene/Ip copolymerization, random copolymers were obtained. Among the used catalysts, catalyst 1 gave the copolymers containing the highest amount of Ip. The copolymers prepared with catalyst 1 showed a steep melting point depression with increasing Ip content because of the high ratio of 1,4-inserted Ip units and/or the low molecular weights of the copolymers.