POLYMERIZATION PROCESS PROVIDING POLYETHYLENE OF ENHANCED OPTICAL PROPERTIES

A process for the polymerization of ethylene to provide an ethylene polymer of reduced Yellowness Index. A feed stream, comprising an inert hydrocarbon diluent containing ethylene in a minor amount, is supplied to a polymerization reactor. A chromium-based polymerization catalyst and a triethylboron co-catalyst are incorporated into the feed stream within the reactor. The polymerization catalyst will normally be used in an amount within the range of 0.008-0.1 wt. % of the diluent in the feed stream and the triethylboron co-catalyst is incorporated in an amount within the range of 0.1-50 ppm of the diluent. The polymer fluff from the reactor is heated to a temperature sufficient to melt the fluff which is then extruded to produce a polymer product. The Yellowness Index after high temperature aging is at least 5% less than the corresponding Yellowness Index of a corresponding polymer product produced without the triethylboron co-catalyst.