Thermoplastic Elastomers Based on Block Copolymers of Ethylene and Propylene

Abstract

Polyolefins having the melt processability of thermoplastics but the solid state properties of elastomers are clearly attractive products for a broad range of applications. Commercially available olefin-based thermoplastic elastomers fall into three major categories: simple alloys of crystalline polypropylene with ethylene-propylene rubber, EPR; similar alloys in which the rubbery phase, EPDM, ethylene-propylene-diene rubber, is partially crosslinked; and those in which the rubber is completely cross linked. Many of the simple polypropylene-EPR alloys are in situ blends made by sequential feeds to the polymerization reactor; others are mechanical blends of separately polymerized polypropylene and EPR. In the latter two cases, crosslinking is induced during melt processing of the blend. Because of the crosslinking in these materials, recycle-processing, if possible, is usually difficult. Simple alloys, on the other hand, while easier to reprocess, are often inferior in tensile properties.