Übergangsmetall-Katalysatoren für die Olefinpolymerisation: 1. Die Niederdrucksynthese von Polyethen

Abstract

The preparation of a variety of polyethene products can be accomplished either by radical mechanisms or by transition metal catalyzed polyinsertions of ethene monomers into metal-carbon bonds. The first attempt requires rigorous conditions, like high pressure and high temperature and leads to branched polyolefin products. The catalyzed process can be pelformed at low pressure and at ambient temperature. Variations in the catalyst composition allow an effective control of the polymer parameters, such as molecular weight, molecular weight distribution, and comonomer content. The present review focuses on reaction mechanisms and on the development of high-mileage transition metal catalysts, based on Ti^III, Zr^IV, and Cr^II, as active species. The usage of these catalysts in different polymerization processes is discussed with respect to the properties of the resulting polyethene commodities.