ABSTRACT
This chapter covers butyl rubber, a special-purpose rubber that nevertheless is rather widely used, and ethylene propylene rubbers, the latest type of synthetic rubber with significant volume. Butyl's outstanding property is its low permeability to gases. The manufacture of butyl rubber is continuous, a solution polymerization being used with methyl chloride as the carrier solvent. Ethylene propylene rubbers are of two types: copolymers and terpolymers. The copolymers, consisting only of ethylene and propylene, are saturated and therefore cannot be vulcanized by conventional means. An outstanding property of terpolymers is the high loading of oil and fillers that can be used with them, and yet the compound shows rubbery properties. When regular butyls are used for compounding, the appropriate grade is chosen on the basis of the amount of unsaturation in the polymer, then on the Mooney viscosity. In commercial compounding the quinoid and resin cures are unique to butyl.
