Polyolefin Elastomers Based on Ethylene and Propylene

Abstract

Abstract In 1940, the first all-hydrocarbon elastomer containing limited olefinic functionality, butyl rubber, was announced. Because of its resistance to em-brittlement on aging, cracking on exposure to ozone, its impermeability to gases, and high damping capacity, this elastomer found use in inner tubes, cable insulation and miscellaneous hose, grommet, and gasket applications, generally lumped together as mechanical goods. It was the chemist's desire to prepare elastomers from other simple, inexpensive olefins, varying the structure to meet property requirements and using limited functionality to accommodate vulcanization. But no such preparative scheme was found, and, instead, attention was turned to modifications of known, substantially saturated hydrocarbon polymers to effect elastomeric properties and vulcanizability or to prepare elastomers from other raw materials, typical examples being Hypalon (chlorosulfonated, low density polyethylene) and polymers derived from epoxides and acrylates. However, K. Ziegler and coworkers pursued the matter of dimerization or oligomerization of olefins with metal alkyls until a breakthrough was made, and the catalyst system now known as Ziegler or Mulheim catalysts was discovered. This basic discovery, initially applied to the polymerization of ethylene, was expanded by Natta and his group and others to preparation of entirely new polymer structures. And, while attention was initially devoted to the preparation of miscellaneous stereoregular, crystalline homopolymers from simple olefins, it was virtually axiomatic that it would inevitably turn to the preparation of elastomeric copolymers. So, like the development of butyl rubber from polyisobutylene, ethylene/propylene elastomers (EPM) were followed by their olefin-containing terpolymers (EPDM), all of which are commercially prepared today. The Nobel Prize Award addresses by each of these aforementioned men trace the history of this important step forward in organometallic catalysis and polymer science.