Copolymerization of ethylene and non-conjugated dienes with Cp₂ZrCl₂/MAO catalyst system: Effect of polymerization temperature on the copolymer structure

Ethylene was copolymerized with linear, non-conjugated dienes by the metallocene catalyst system Cp₂ZrCl₂/MAO at several temperatures from 20 to 80°C. The dienes were 1,5-hexadiene (HD), 1,7-octadiene (OD) and 7-methyl-1,6-octadiene (MOD). Incorporation of the dienes was studied by ¹H  and ¹³C  NMR and FTIR. Polymerization conditions had a dramatic effect on the degree of crosslinking of the product. At polymerization temperatures from 20 to 65°C the copolymers of ethylene and HD or OD were nearly totally crosslinked, whereas at 80°C the degree of crosslinking was consistently under 10%. When MOD was used as comonomer the degree of crosslinking did not increase above 40% even for copolymer produced at 20°C.