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

✍ Scribed by Esa Kokko; Anneli Malmberg; Petri Lehmus; Barbro Löfgren; Jukka V. Seppälä

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 205 KB
• Volume: 38
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(20000115)38:2<376::aid-pola12>3.0.co;2-5

✦ Synopsis

A study was made on the effects of polymerization conditions on the long-chain branching, molecular weight, and end-group types of polyethene produced with the metallocene-catalyst systems Et[Ind] 2 ZrCl 2 /MAO, Et[IndH 4 ] 2 ZrCl 2 /MAO, and (n-BuCp) 2 ZrCl 2 /MAO. Long-chain branching in the polyethenes, as measured by dynamic rheometry, depended heavily on the catalyst and polymerization conditions. In a semibatch flow reactor, the level of branching in the polyethenes produced with Et[Ind] 2 ZrCl 2 /MAO increased as the ethene concentration decreased or the polymerization time increased. The introduction of hydrogen or comonomer suppressed branching. Under similar polymerization conditions, the two other catalyst systems, (n-BuCp) 2 ZrCl 2 /MAO and Et[IndH 4 ] 2 ZrCl 2 /MAO, produced linear or only slightly branched polyethene. On the basis of an end-group analysis by FTIR and molecular weight analysis by GPC, we concluded that a chain transfer to ethene was the prevailing termination mechanism with Et[Ind] 2 ZrCl 2 /MAO at 80 °C in toluene. For the other catalyst systems, ␤-H elimination dominated at low ethene concentrations.