Copolymerization of ethylene and 1,5-hexadiene with zirconocene catalysts

Copolymerization of ethylene and 1,5-hexadiene (HD) was carried out with non-bridged or bridged zirconocene catalysts using methylaluminoxane (MAO) as a cocatalyst. The resulting copolymers were extracted with boiling o-dichlorobenzene (ODCB) to fractionate into soluble and insoluble parts. The ligand structure of zirconocenes, the feed ratio of HD, and the catalyst concentration strongly affected the copolymer composition. In the copolymerization with non-bridged zirconocene catalysts, the amount of boiling ODCB-soluble part decreased with increasing HD content in the copolymer. On the other hand, with bridged zirconocene catalysts, it increased with increasing HD content in the copolymer. The bridged zirconocene catalysts were apt to take in more HD than non-bridged catalysts. Effect of catalyst concentration was investigated in relation to crosslinking reaction. Temperature-rising elution fractionation (TREF) of the boiling ODCB-soluble part was conducted to show the occurrence of heterogenous composition in copolymers obtained with some specific zirconocene catalysts.