GB785174A - A process for the production of emulsions - Google Patents

Abstract

An emulsion is made by polymerizing or copolymerizing one or more organosiloxanes of the general formula RnSiO 4-n/2 , wherein each R is a monovalent hydrocarbon or halogenated hydrocarbon radical, some of which may be replaced by H atoms, and n has an average value from 1 to below 3, while the siloxane(s) is dispersed in a finely-divided state in an aqueous medium by reacting the dispersed siloxane(s) with a catalyst which is a strong mineral acid or a strongly alkaline compound. The process may be effected either by dispersing the siloxane in water, preferably by using an emulsifying agent, adding the catalyst thereto and allowing the emulsion to stand, with or without agitation, at the desired temperature until the siloxane has reached the desired size of molecular aggregation, or by adding the catalyst to the siloxane prior to or simultaneously with dispersion. Preferably an emulsifying agent is dispersed in the siloxane and the mixture is then added with agitation to water to give the desired emulsion and the catalyst is then added and polymerization allowed to proceed. Polymerization may be effected at room temperature, or at above 100 DEG C. in a closed system, but preferably at 25 DEG to 80 DEG C. The siloxane may be recovered from the emulsion merely by breaking the latter, e.g. by adding salts such as NaCl or by evaporating the water. If the viscosity of the initial siloxane is too high for adequate dispersion, a little solvent may be used. Siloxanes specified contain saturated, unsaturated, cyclic or halogenated aliphatic or aromatic or halogenated aromatic hydrocarbon radicals or H atoms. The final siloxanes may contain hydroxyl terminal groups. Catalysts specified are HCl, HBr, HI, H2SO4, HNO3, H3PO4 NaOH, CsOH, LiOH and quaternary ammonium hydroxides of the formula R14NOH, where each R1 is an alkyl, aralkyl or hydroxyalkyl radical, or their salts, and are used in amount, e.g. of 1 alkali mol. per 100 to 50,000 Si atoms, or 15 to 80 per cent of acid based on the weight of the aqueous phase of the emulsion. Where quaternary ammonium salts are used, acids or alkaline materials must be added to effect polymerization. Many cationic, anionic and non-ionic emulsifying agents are specified. The emulsions may be used for release agents or for coating compositions, particularly latex paints. Examples are given.