Fluoropolymer containing a small amount of bromine-containing olefin units

Claim 1

As a novel fluoropolymer, a copolymer whose interpolymerized units consist essentially of a. up to 3 mole %, based on the total moles of components (a) and (b), of units derived from a compound selected from the group: bromotrifluoroethylene and 4-bromo-3,3,4,4-tetrafluorobutene-1, with the proviso that enough of such units are present to provide at least 0.05 weight % bromine in the copolymer, and b. enough units derived from component (b-1), (b-2) or (b-3) as follows to make up the remainder of the copolymer: b-1. tetrafluoroethylene and a perfluoroalkyl perfluorovinyl ether wherein the alkyl group contains 1-5 carbon atoms, b-2. about 45-65 mole % of tetrafluoroethylene, about 20-55 mole % of a C 2 -C 4 olefinic hydrocarbon and from 0 to about 30 mole % vinylidene fluoride, or b-3. vinylidene fluoride, at least one fluorine-containing olefin copolymerizable therewith, and optionally said perfluoroalkyl perfluorovinyl ether, said olefin being a compound which contains 2-7 carbon atoms, contains no bromine atom, and contains at least as many fluorine atoms as carbon atoms.