Process for production of chlorinated ethylene-propylene copolymers

A method for producing a chlorinated ethylene-propylene copolymer comprising contacting a starting ethylene-propylene copolymer, wherein the propylene content is 20 to 38% by weight, the melt flow index is 0.01 to 5.0 g/10 minutes, the melting peak as measured by differential scan calorimetry (DSC) is 80.degree. C. or more, the crystallinity as measured by X-rays is 3 to 45%, the index M.sub.W /M.sub.N of the distribution of molecular weight, determined by gel permeation chromatography (GPC), is greater than 4, and the Mooney viscosity (ML.sub.1+4, 100.degree. C.) is 10 to 180, with chlorine gas in an aqueous suspension, to produce a chlorinated ethylene-propylene copolymer having a chlorine content of 20 to 45% by weight and a Mooney viscosity (ML.sub.1+4, 100.degree. C.) of 10 to 150, wherein

• at a first stage, 20 to 60% of the total chlorination amount is chlorinated at a temperature at least 25.degree. C. below the melting point of the ethylene-propylene copolymer but higher than 50.degree. C.,
• at a second stage, at least 30% of the remaining chlorination amount is chlorinated at a temperature 10.degree. C. or more higher than the chlorination temperature at the first stage but at a temperature 5.degree. to 15.degree. C. lower than the melting point of said ethylene-propylene copolymer, with 60 to 90% of the total chlorination amount chlorinated up to that Stage, and
• at a third stage, at least 10% of the total chlorination amount is chlorinated at a temperature less than the melting point of the ethylene-propylene copolymer but not less than a temperature of the melting point minus 2.degree. C.