SYNTHESIS OF HYPERBRANCHED POLYETHYLENE AND POLYETHYLENE-GRAFTED POLYSTYRENE CATALYZED BY A π-(METHALLYL)NICKEL HALIDE/LEWIS ACID SYSTEM

摘要

Until recently, most systems for the polymerization of ethylene and a-olefins have required the use of early transition metal catalysts.1 These processes produce highly linear materials which are crystalline, insoluble solids. Species containing greater than eighteen carbons must contain branches in order to remain in the liquid state. Most catalytic systems using late transition metals such as nickel are capable of producing only dimers or low molecular weight oligomers with a degree of polymerization less than twenty. This is due to unfavorable, rapid p-hydride elimination in competition with chain propagation. Currently, only one late transition metal system has been developed to produce branched polyolefins.3 However, these catalysts produce amorphous materials with a relatively low ratio of methyl groups to total number of carbon atoms. In contrast, hyperbranched polyolefins are liquids containing a high branch quantity. These materials are potentially useful in applications such as lubricating oils.