Preparation of highly branched polyethylene using (alpha-diimine) nickel complex covalently supported on modified SiO2

摘要

Bis(4-(4-amine-3,5-diisopropylbenzyl)-2,6-diisopropylphenylimino) acenaphthene NiBr2 (Catalyst 1) was synthesized. The complex covalently supported on Et3Al-treated silica (SC) and used for ethylene polymerization was produced with cocatalyst of common inexpensive alkylaluminum compounds. Polyethylenes (PEs) with branching numbers of 12.94 (1000C) to 116.02 (1000C) were prepared in heptane. The polymerization conditions, such as the cocatalyst, Al/Ni ratio, and temperature, had significant effects on catalytic activity and properties of polyethylenes. Confirmed by high-temperature C-13 NMR, the polyethylenes synthesized contain significant amounts of not only methyl but also ethyl, propyl, butyl, pentyl, and other long branches (longer than six carbons). The branching degree of polyethylenes increased with temperature, while their molecular weight and melting point decreased correspondingly, resulting in linear semicrystalline to totally amorphous polymers. The formation of the branches could be illustrated by the chain walking mechanism, which controlled their specific spacing and conformational arrangements with one another. (c) 2006 Wiley Periodicals, Inc.