Ethylene/1-hexene copolymerizations by syndioselective metallocenes: Direct comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

Copolymerizations of ethylene with l-hexene have been carried out by using two metallocenes: highly syndiospecific isopropylidene(1-eta(5)-cyclopentad ienyl)( 1-eta(5)-fluorenyl)-dimethylzirconium (Me2C(Flu)(Cp)ZrMe2, 1) and l ess syndiospecific (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium (Et(Flu)(Cp)ZrMe2, 2), in the presence of [Ph3C] [B(C6F5)(4)] as a cocatal yst. The effect of different types of bridges on the catalytic activity and comonomer reactivity was reported. The ethano bridged 2 compound of a smal ler dihedral angle showed much higher activity than the 1 compound in the e thylene homo- and copolymerizations. The catalytic activities of the two co mpounds were enhanced about twice when a suitable amount of l-hexene comono mer is present in the feed. The copolymerization of ethylene with l-hexene revealed a noticeable influence of the type of bridge on the relative react ivity of the l-hexene. C-13-NMR analysis of copolymers showed that compound 1 is characterized by lower r(E), taken as an index of ethylene reactivity , and higher reactivity of l-hexene. The bridge also affects the distributi on of the l-hexene along the copolymer chain, investigated through their pr oduct of reactivity ratios, r(E)r(H). The thermal properties and the densit y of copolymers were not affected by the type of bridge of the metallocenes , but mainly depended on l-hexene content in the copolymer. (C) 1999 John W iley & Sons, Inc.