Process for the setabilization of fluoropolymers

Claim 1

A process for improving the high temperature stability of a melt-processible copolymer of at least two comonomers selected from the group consisting of tetrafluoroethylene; chlorotrifluoroethylene; R f CF═CF 2 , where R f is a primary fluoroalkyl group with 1-5 carbon atoms; R g OCF═CF 2 , where R g is R f or a primary fluoroalkyl group containing ether oxygen and 4-12 carbon atoms; and a fluorodioxole having the following formula ##STR3## where each one of R and R, independently is fluorine or the trifluoromethyl group; said process comprising at least one cycle of the following sequential steps: (a) contacting said copolymer for a period of at least 15 minutes at a temperature between about 25° C. and 200° C. with at least a stoichiometric amount, based on the concentration of --COOH and --COF groups, of an anhydrous or aqueous stabilizing agent selected from the group consisting of (1) bases selected from organic amines having a boiling point at normal pressure of at most about 130° C., and (2) tertiary alcohols with up to 8 carbon atoms, to form an intermediate; (b) isolating and drying the intermediate at a temperature between about 70° C. and 150° C.: (c) converting the dried intermediate to a copolymer having improved thermal stability by contacting the intermediate with fluorine at a temperature between 20° C. and the lowest temperature at which the copolymer exhibits a solid state transition, whether first order or second order, and (d) removing excess fluorine and volatile by-products from the reaction product and recovering the copolymer.