Synthesis of the Ethylene-Hexafluoropropene Copolymers by High Pressure Copolymerization and Their Elastic Propertiest

Abstract

The ethylene-hexafluoropropene (HFP) copolymers were synthesized both by batch-wise and continuous copolymerization processes under high pressure. By a batch-wise process (650-1385kg/cm², 115-155°C), no ethylene-HFP copolymer containing more than 50 mol% of HFP was obtained, and the azeotropic composition was 0.265. Under almost the same conditions (pressure, temperature and concentration of initiator), no homopolymerization reaction of HFP occured. The experimental data were analyzed according to the Barb's theory and the possibility of thepresence of the reactantsof 1 : 1 complex of ethylene-HFP during the reaction was presumed. The vulcanizability and elastic properties of the copolymers synthesized by a continuous process (1600-2000kg/cm², 160-200°C) were evaluated. It was found that the copolymers were not vulcanized with diamines but only with organic peroxides. The vulcanized copolymers containing 35mol% of HFP have the following characteristics as an elastomer : adequate heat resistance at 200°C and low compression set at high temperature, good oil-, chemical- and steam-resistance, excellent electrical properties, and favorable vulcanizability ofcomposed materials with other synthetic rubbers. The characteristics of the vulcanized copolymers were also compared with those of heat-resistant rubbers.