Thermoset elastomers

Abstract

Elastomers are defined by their very large deformability with essentially complete recoverability. In order for a material to exhibit this type of elasticity, three molecular requirements must be met: the material must consist of polymeric chains, the chains must have a high degree of flexibility and mobility, and the chains must be joined into a network structure. Some polymers are not elastomeric under normal conditions but can be made so by raising the temperature or adding a diluent (“plasticizer”). Polyethylene is in this category because of its high degree of crystallinity. Polystyrene, poly (vinyl chloride), and the biopolymer elastin are also of this type, but because of their relatively high glass transition temperatures, they require elevated temperatures or addition of diluent to become elastomeric. There is a real need for more high-performance elastomers, which are materials that remain elastomeric at very low temperatures and are relatively stable at very high temperatures. These polymers have rather low glass transition temperatures in spite of the fact that the skeletal bonds of the chains are thought to have some double-bond character. There are, thus, a number of interesting problems related to the elastomeric behavior of these unusual semi-inorganic polymers. There is also increasing interest in the study of elastomers that also exhibit mesomorphic behavior.