GB719950A - Improvements in or relating to the manufacture of fluorine-containing polymers - Google Patents

Abstract

Fluorine-containing polymers (except the homopolymer of tetrafluoethylene) are made by polymerizing a substituted ethylene having at least two fluorine atoms in the presence of an aqueous suspension medium containing a water-soluble salt of a peracid as a promoter, a water-soluble reducing agent as an activator and an inorganic water-soluble salt which in its oxidized state is more readily reducible than the promoter and in its reduced state is more readily oxidizable than the activator. Specified fluorine-containing polymers are trifluorochloroethylene, perflurobutadiene, perfluoropropene, phenyl-trifluoroethylene, alpha-methyl-phenyl-difluoroethylene, perfluoroacrylonitrile, perfluorostyrene, perfluorocyclobutene, perfluorocyclobutadiene, vinyl fluoride, trifluoroethylene and difluorodichloroethylene, and their copolymers with each other or with tetrafluoroethylene, vinyl chloride and vinylidene chloride. Specified peracids are the sodium, potassium, calcium, barium and ammonium salts of persulphuric and perphosphoric acids: specified activators are sodium bisulphate, hydrosulphite, thiosulphate and trimethylamine and specified salts are the hydroxides, carbonates, sulphates, phosphates, nitrates and chlorides of cobalt, silver, copper, nickel, molybdenum, iodine and, preferably, iron, manganese and chromium. Suitable concentrations of promoter, and of activator, lies within the range 0.003 molar to 0.1 molar, while the concentration of inorganic salt is preferably maintained between 5 and 300 p.p.m. in the aqueous phase during the polymerization. The polymerization may take place in either a batchwise or continuous manner preferably using buffering agents such as borax, disodium phosphate, sodium carbonate, ammonium carbonate, sodium acetate, acetic acid, propionic acid and monosodium phosphate to produce optimum pH conditions. Fillers such as titanium oxide, carbon black, clays, asbestos, and glass fibre may be added before polymerization. The polymerization vessel may be made of or lined with, stainless steel, "Insonel" (R.T.M.), "Monel" (R.T.M.), silver, nickel, glass or fluorinated solid polymers.