Influence of the catalyst and polymerization conditions on the long-chain branching of metallocene-catalyzed polyethenes

A study was made on the effects of polymerization conditions on the long-ch ain branching, molecular weight, and end-group types of polyethene produced with the metallocene-catalyst systems Et[Ind](2)ZrCl2/MAO, Et[IndH(4)](2)Z rCl2/MAO, and (n-BuCp)(2)ZrCl2/MAO. Long-chain branching in the polyethenes , as measured by dynamic rheometry, depended heavily on the catalyst and po lymerization conditions. In a semibatch flow reactor, the level of branchin g in the polyethenes produced with Et[Ind](2)ZrCl2/MAO increased as the eth ene concentration decreased or the polymerization time increased. The intro duction of hydrogen or comonomer suppressed branching. Under similar polyme rization conditions, the two other catalyst systems, (n-BuCp)(2)ZrCl2ZrCl2/ MAO and Et[IndH(4)](2)ZrCl2/MAO, produced linear or only slightly branched polyethene. On the basis of an end-group analysis by FTIR and molecular wei ght analysis by GPC, we concluded that a chain transfer to ethene was the p revailing termination mechanism with Et[Ind](2)ZrCl2/MAO at 80 degrees C in toluene. For the other catalyst systems, beta-H elimination dominated at l ow ethene concentrations. (C) 2000 John Wiley & Sons, Inc.