Process for the preparation of aqueous, colloidal dispersions of

Abstract

An improved process for the preparation of aqueous, colloidal dispersions of copolymers comprising at most 60 mole % of units of tetrafluoroethylene, 60 to 40 mole % of units of ethylene and 0 to 15 mole % of units of at least one other .alpha.-olefinic monomer, which can be copolymerized with tetrafluoroethylene and ethylene, in the presence of manganese compounds as the catalyst is described. In this process, the emulsion polymerization is carried out in an aqueous phase in the presence (a) of a chain transfer agent of the formula X--CH.sub.2 --COOR (X=Cl, Br, COOH, COOR, COCH.sub.3, CH.sub.3, C.sub.2 H.sub.5 or C.sub.3 H.sub.7 ; and R=C.sub.1 -C.sub.4 -alkyl), and (b) of a compound which stabilizes the dispersion and has the formula ##STR1## (Y=COONH.sub.4, COOH, CH.sub.3, CH.sub.2 OH, CH.sub.2 COOH or CH.sub.2 COONH.sub.4). (b) can additionally contain an ammonium salt of an inorganic non-metal acid, for example ammonium chloride or fluoride. Terpolymers or quaterpolymers containing, in addition to tetrafluoroethylene and ethylene, preferably hexafluoropropylene and/or a 'bulky' vinyl monomer as the third and/or fourth comonomer are preferably prepared. The copolymer dispersions thus prepared have very low coagulate contents and are very stable and the copolymers have melt flow indices most appropriate to the processing operations. They can be processed to coatings and shaped articles.