COPOLYMERIZATION OF ETHENE WITH STYRENE USING METHYLALUMINOXANE-ACTIVATED BIS(PHENOLATE) COMPLEXES

Ethene was copolymerized with styrene using different titanium bis(phe nolate) complexes [R(1)(4,6-R(2)C(6)H(2)-O)(2)]TiX(2) (R(1) = CH2, C2H 4, S, SO; R(2) = CR(3), t-Bu; X Cl, O(i-Pr)) activated with methylalum inoxane. The influence of ligand substitution pattern and polymerizati on conditions on catalyst activity, polymerization kinetics, styrene i ncorporation, molecular mass, and copolymer microstructure was investi gated. Catalyst activity increased with decreasing styrene concentrati on and was affected by the type of the bridging group R(1) with an act ivity rating of R(1) = S > SO > C2H4. The opposite trend was observed for styrene incorporation where R(1) = C2H4 gave the highest styrene c ontent. Polymerization kinetics primarily depended upon complex struct ure and was only marginally influenced by polymerization conditions. A s a rule, styrene contents of more than 90 mol % in the monomer feed w ere needed to achieve more than 20 mol % styrene incorporation in the copolymer. Copolymerization parameters were calculated for ethene/styr ene copolymerization using [S(4-Me-6-t-BuC(6)H(2)O)(2)]Ti(O-i-Pr)(2) t o 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 extr action of copolymers with subsequent NMR analysis revealed the presenc e of random poly(ethener-co-styrene) with inhomogeneity with respect t o 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/sty rene copolymer was detected.