Preparation of polyethylene in solution

Polyethylene was prepared in a homogeneous system at 120°C. Several catalytic systems were employed, all using a soluble vanadium compound. The first consisted of an alkylaluminum compound in conjunction with the vanadium compound and a “promoter.” This promoter, which is believed to act as an oxidizing agent to reactivate dead catalyst sites, was a polyhalo compound with esters of trichloroacetic acid preferred. The promoter was added continuously throughout the polymerization. Polyethylene so produced had a narrow Mw/Mn ratio close to the theoretical ratio of 2.0 for a single catalyst site. Up to 266 polymer chains were produced per vanadium atom. In the second system, the cocatalyst was an AlBr3(AlCl3)–(C6H5)4Sn[(C6H5)3Bi] combination. The continuous addition of a promoter such as methyl trichloroacetate was necessary, presumably to reactivate dead catalytic sites. By this procedure, yields up to 6.6 kg of polymer per millimole of vanadium and 30–60 chains per vanadium atom were achieved. The product had a narrow Mw/Mn ratio of 2.4 by gel-permeation chromatography (GPC). A study of the interactions of the catalyst compounds indicated that CCl3COOR does oxidize di- and trivalent vanadium.