Copolymerization of ethylene and 1,7-octadiene, 1,9-decadiene with zirconocene catalysts

Copolymerizations of ethylene and 1,7-octadiene (OD) and 1,9-decadiene (DD) were investigated with various non-bridged and bridged zirconocene catalysts using methylisobutylaluminoxane as a cocatalyst. The resulting copolymers were extracted with boiling o-dichlorobenzene (ODCB), and the structure of the boiling ODCB-soluble part was studied by ¹H, ¹³C NMR and DEPT (distortionless enhancement of polarization transfer) spectroscopy. In the case of ethylene/OD copolymerization, the ligand structure of the zirconocene catalysts strongly affected the propagation mode of OD. The zirconocene catalysts having cyclopentadienyl or pentamethylcyclopentadienyl ligands gave copolymers having 1-hexenyl and 1,3-disubstituted cycloheptane units, derived from 1,2-addition propagation and addition - cyclization propagation of OD, respectively. On the other hand, the zirconocene catalysts with indenyl ligand produced the copolymers having exclusively 1,3-disubstituted cycloheptane units. Furthermore, the copolymer prepared by diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride was crosslinked. The diastereostructure of the 1,3-disubstituted cycloheptane units in the copolymers was not influenced by the stereospecificity of the catalysts used, and a cis-structure was preferentially formed. In the case of the copolymerization of ethylene and DD, the C_2v- symmetric zirconocene catalysts produced the copolymers with 1-octenyl branches derived from 1,2-addition propagation of DD. Other C₂- and C_s-symmetric zirconocene catalysts with bulky ligands yielded copolymers with crosslinking structures derived form addition propagation of sidechain unsaturated bond of 1,2-added DD units.