Studies on Properties of Metallocene Catalysed Copolymers of Ethylene and Linear, Non-conjugated Dienes

The effect of diene addition on the structure of ethylene copolymer was studied. The dienes used were 1,5-hexadiene (HD), 1,7-octadiene (OD), and 7-methyl-l,6-octadiene (MOD).Polymerizations were conducted in n-heptane in the presence of the metallocene catalyst cyclopentadienyl zirconium dichloride (Cp₂ZrCl₂) with methylaluminoxane (MAO) as a cocatalyst. The structure of the copolymer was determined by NMR-techniques. The 1,5-hexadiene comonomer was predominantly incorporated as a 5 member ring structure into the polyethylene backbone. OD and MOD formed branches in the polyethylene chain. The ethylene/HD copolymers were analysed using dynamic rheometry to study the effect of ring structures on the rheological properties of the product. The ring structures stiffen the chain, which was manifested as increasing viscosity and shear sensitivity of the melt. At low hexadiene ring content, the effect of the ring structure was masked by the long chain branching already present in the ethylene homopolymer.