Long-chain-branched polyethene by the copolymerization of ethene and nonconjugated alpha,omega-dienes

Ethene was copolymerized (1) with 1,5-hexadiene with rac-ethylenebis(indeny l)zirconium dichloride/methylaluminoxane (MAO) used as a catalyst and (2) w ith 1,7-octadiene with bis(n-butylcyclopentadienyl)zirconium dichloride/MA0 and rac-ethylenebis(indenyl)hafnium dichloride (Et[Ind](2)HfCl2)/MAO used as catalysts at 80 degreesC in toluene. The copolymer microstructure and th e influence of diene incorporation on the rheological properties were exami ned. Ethene and 1,5-hexadiene formed a copolymer in which a major fraction of the 1,5-hexadiene was incorporated into rings and a small fraction forme d 1-butenyl branches. The copolymerization of ethene with 1,7-octadiene res ulted in a higher selectivity toward branch formation. Some of the branches formed long-chain-branching (LCB) structures. The ring formation selectivi ty increased with decreasing ethene concentration in the polymerization rea ctor. Melt rheological properties of the diene copolymers resembled those o f metallocene-catalyzed LCB homopolyethenes and depended on the vinyl conte nt, the catalyst, and the polymerization conditions. At high diene contents , all three catalysts produced crosslinked polyethene. This was especially pronounced with Et[Ind](2)HfCl2, where only 0.2 mol % 1,7-octadiene in the copolymer was required to achieve significantly modified rheological proper ties, (C) 2001 John Wiley & Sons, Inc.