Plasticization of Polyolefin Elastomers, Semicrystalline Plastics and Blends Crosslinked in situ during Melt Mixing

Abstract

Abstract Semi-crystalline polyolefins, e.g. , polypropylene in its isotactic and syndiotactic forms, become brittle at low temperature due to their inherent crystallinity and relatively high T g . It has been discovered that certain “non-polar” aliphatic esters, in particular monomeric tallates and sebacates can effect a large depression in T g of the polypropylene amorphous component which is in line with free volume considerations. The melting point of the crystalline fraction was also depressed albeit to a much smaller extent. This successful plasticization of polypropylene was applied to heterophase systems with the elastomer crosslinked in situ during melt blending with polypropylene and in the presence of a plasticizer. The plasticizer was distributed in both polymer components of the blend. Therefore the glass transition temperatures of both the polypropylene and the elastomer phases could be greatly depressed through simultaneous plasticization of both polymer phases resulting in a supertough material at −40°C and below. Since only the amorphous component of polypropylene is plasticized, the crystalline fraction is not much affected and the upper service temperature range is maintained. The resulting TPEs have an excellent balance of engineering properties to −125°C and are much more elastic than unplasticized TPEs due to the suppression of yielding behavior.