Elastomer blends distinct polymers

Such rubbery and thermoplastic polymers may be blended in any proportion, so that on one hand the product may be considered as a thermoplastic elastomer, and on the other as an elastomer-modified thermoplastic. There is, furthermore, a spectrum of intermediate materials, including those which might be considered as leather-like. In this area the distinction between rubber and plastics material becomes very blurred. 

Common examples of miscible blends are ethylene-propylene copolymers of different composition that result in an elastomer comprising a semicrystalline, higher ethylene content and an amorphous, lower ethylene content components. These blends combine the higher tensile strength of the semicrystaUine polymers and the favorable low temperature properties of amorphous polymers. Chemical differences in miscible blends of ethylene-propylene and styrene-butadiene copolymers can also arise from differences in the distribution and the type of vulcanization site on the elastomer. The uneven distribution of diene, which is the site for vulcanization in blends of ethylene-propylene-diene elastomers, can lead to the formation of two distinct, intermingled vulcanization networks. 

Block copolymers are long-chain molecules composed of multiple blocks of distinct monomers (see Fig. 17). They are widely used as adhesives, and because they can reduce interfacial energy they can act as compatibilizers in polymer blends. In addition, many of the novel and fascinating properties of block copolymers arise from microphase separation. Thermoplastic elastomers, such as polyurethanes and polystyrene-polyisoprene-polystyrene triblock copolymers, act like cross-linked elastomers, although there is no true cross-linking. Instead, rubbery portions of the... 

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