Also found in: Acronyms.
any of the synthetic rubbers produced by the copolymerization of ethylene with propylene or the terpolymerization of these two monomers with a diolefin containing unconjugated double bonds. Such a diolefin would be 1,4-hexadiene (CH2═CH—CH2—CH═CH—CH3).
Recurring units of propylene constitute 20 to 60 percent of the ethylene-propylene macromolecule, and diolefin units account for 0.5 to 3.0 percent. Ethylene-propylene rubbers have a molecular weight of 80,000 to 250,000, a density of 0.85 to 0.87 g/cm3, and a glasstransition temperature of –55° to –70°C. Their volume resistivity is 5 × 1015 ohm-cm, and their dielectric strength is 28 to 32 megawatts per m; the tangent of the dielectric loss angle ranges from 1 × 10”3to2 × 10–3.
Ethylene-propylene rubbers are produced by ionic coordination polymerization in hydrocarbons used as solvents, such as n-hexane. Those rubbers that are synthesized from a mixture of three monomers are known in the USSR under the trade name SKEPT; they contain unsaturated bonds and can therefore be vulcanized by the usual method, with systems based on sulfur. Copolymers of ethylene with propylene are known in the USSR under the trade name SKEP; these rubbers are vulcanized with organic peroxides.
Ethylene-propylene rubbers have good mechanical and elastic properties and good resistance to ozone, heat, frost, organic solvents, bases, and acids. They also have excellent dielectric characteristics. SKEP-type rubbers are used mainly for insulating wires and cables; SKEPT-type rubbers, on the other hand, are used mainly in the production of industrial rubber goods, such as hoses and packings. These rubbers have limited use in the tire industry because of the low strength of their bonding to the cord of the tires.
Trade names of ethylene-propylene rubbers produced outside the USSR include Vistalon (USA), Nordel (USA), Epcar (USA), Dutral (Italy), APTK (Federal Republic of Germany), Keltan (Netherlands), and Esprene EPDM (Japan). In 1976 the world production of ethylene-propylene rubbers was approximately 390,000 metric tons.