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

Abstract

Copolymerizations of ethylene with 1-hexene have been carried out by using two metallocenes: highly syndiospecific isopropylidene(1-η5-cyclopentadienyl)(1-η5-fluorenyl)-dimethylzirconium (Me2C(Flu)(Cp)ZrMe2, 1) and less syndiospecific (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium (Et(Flu)(Cp)ZrMe2, 2), in the presence of [Ph3C][B(C6F5)4] as a cocatalyst. The effect of different types of bridges on the catalytic activity and comonomer reactivity was reported. The ethano bridged 2 compound of a smaller dihedral angle showed much higher activity than the 1 compound in the ethylene homo- and copolymerizations. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1-hexene comonomer is present in the feed. The copolymerization of ethylene with 1-hexene revealed a noticeable influence of the type of bridge on the relative reactivity of the 1-hexene. 13C-NMR analysis of copolymers showed that compound 1 is characterized by lower rE, taken as an index of ethylene reactivity, and higher reactivity of 1-hexene. The bridge also affects the distribution of the 1-hexene along the copolymer chain, investigated through their product of reactivity ratios, rErH. The thermal properties and the density of copolymers were not affected by the type of bridge of the metallocenes, but mainly depended on 1-hexene content in the copolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2763–2772, 1999