Copolymerization of ethene with styrene using methylaluminoxane-activated bis(phenolate) complexes

Ethene was copolymerized with styrene using different titanium bis(phenolate) complexes [R(1)(4,6-R(2)C(6)H(2)-O)(2)]TiX(2) (R(1) = CH2, C2H4, S, SO; R(2) = CR(3), t-Bu; X Cl, O(i-Pr)) activated with methylaluminoxane. The influence of ligand substitution pattern and polymerization conditions on catalyst activity, polymerization kinetics, styrene incorporation, molecular mass, and copolymer microstructure was investigated. Catalyst activity increased with decreasing styrene concentration and was affected by the type of the bridging group R(1) with an activity rating of R(1) = S > SO > C2H4. The opposite trend was observed for styrene incorporation where R(1) = C2H4 gave the highest styrene content. Polymerization kinetics primarily depended upon complex structure and was only marginally influenced by polymerization conditions. As a rule, styrene contents of more than 90 mol % in the monomer feed were needed to achieve more than 20 mol % styrene incorporation in the copolymer. Copolymerization parameters were calculated for ethene/styrene copolymerization using [S(4-Me-6-t-BuC(6)H(2)O)(2)]Ti(O-i-Pr)(2) to be r(E) = 111 and r(S) = 0.055, reflecting a pronounced tendency for ethene and much less for styrene to form long sequences. Solvent extraction of copolymers with subsequent NMR analysis revealed the presence of random poly(ethener-co-styrene) with inhomogeneity with respect to both styrene incorporation and molecular mass distribution, typical for multisite Ziegler-Natta catalysts. In contrast to earlier reports, only traces of syndiotactic polystyrene but no alternating ethene/styrene copolymer was detected.