GB823974A - Fluorine containing copolymers - Google Patents

Abstract

Metals, such as aluminium, and articles of protective clothing are coated with a copolymer of hexafluoropropane and vinylidene fluoride which is applied dissolved in a solvent such as ethyl acetate by conventional techniques such as spraying, dipping or brushing. The coating may be built up by the application of several layers of the coating composition, each layer being permitted to harden by solvent evaporation before the next layer is applied.ALSO:Relates to copolymers of hexafluoropropene and vinylidene fluoride and to terpolymers of these monomers and up to 15 mol. per cent of a third monomer such as 1,1,3-trifluorobutadiene, 1,1,2,2-tetrafluoroethyl vinyl ether and 2,2,2-trifluoroethyl allyl ether. Polymerization is preferably effected in aqueous emulsion in the presence of an organic or inorganic peroxide catalyst or a redox system and an emulsifying agent which may be potassium stearate, sodium oleate or potassium palmitate, or which preferably is the sodium or potassium salt of a halogen-substituted carboxylic acid which is at least half fluorinated and which has between 4 and 20 carbon atoms per molecule, such as perfluorohexanoic, perfluoro-octanoic, 3,5,6-trichlorooctafluorohexanoic and 3,5,7,8-tetrachloroundecafluorohexanoic acid. The pH of the system may be from 2 to 10, preferably from 4 to 8, being maintained by the addition of a buffer such as disodium hydrogen phosphate and sodium metaborate. Polymerization may also be effected in an organic solvent such as hexane, iso-octane, cyclohexane, benzene, toluene, methanol, t-butanol, dioxane, tetrahydrofuran, or preferably a fluorocarbon solvent such as fluorotrichloromethane. Polymerization may be carried out in the presence of fillers such as titanium dioxide, copper and iron powder, mica and asbestos; the preformed polymer may also be mixed with these materials as well as with a high molecular weight polytrifluorochloroethylene to improve impact strength. The molecular weight of the polymer product may be controlled by the presence or absence in the reaction medium of a modifier such as chloroform, 1,1,2 - trichlorotrifluoroethane, carbon tetrachloride, bromotrichloromethane, trichloroacetyl chloride and dodecyl mercaptan. In an example the copolymer is vulcanized by heating under pressure with a mixture of benzoyl peroxide, disodium phosphite and zinc oxide. Solutions of the copolymers in a solvent such as methyl, ethyl or butyl acetate may be used as coating compositions.