Polymerisation of unsaturated organic compounds

Polymerizable unsaturated organic compounds are polymerized in aqueous dispersion by subjecting them to intermittent illumination. One or more photo-initiators may be present. If more than one is used they should be sensitive to light in different sections of the spectrum. The initiators may be of the kind that dissoci ate into free radicals or which produce free radicals by an electron transfer reaction. Examples given are: 1-chloroanthraquinone, azo-bis-iso-butyronitrile, diacetyl, benzin, benzoin, anthraquinone, N-bromosuccinimide, di-chloramine, diazonium salts, e.g. salts of diazotized sulphanilic acid, iron salts, parabromo phenacyl bromide, uranyl nitrate and uranium dioxide. Benzoin and uranyl nitrate may be used in combination. The illumination periods may vary from 0.005 to 0.5 seconds while the dark periods are preferably not less than 0.2 seconds and in any event not less than twice the length of the light period. The process may be effected using a central lamp and rotating reflector surrounded by a circle of transparent vessels holding the dispersion, or by circulating the dispersion through an illuminated chamber. Emulsions, which are opaque, should be stirred to distribute the irradiated surface layer throughout the emulsion. Monomers referred to are vinyl ketones, e.g. vinyl methyl ketone, acrylate esters, e.g. methyl and ethyl acrylate, vinylidene chloride, vinyl chloride, vinyl acetate, methyl methacrylate, styrene and butadiene. Copolymers may be prepared. In Examples 1 to 4 aqueous emulsions of vinyl acetate are polymerized under various conditions and in Example 5 a mixture of butadiene and styrene. The emulsions consisted of (1) vinyl acetate, sulphated methyl oleate and uranyl nitrate; (2) vinyl acetate, gum acacia and azo-bis-isobutyronitrile; (3) vinyl acetate, sulphated methyl oleate and azo-bis-isobutyrinitrile; (4) vinyl acetate, gum acadia and p-bromophenacyl bromide; (5) butadiene/styrene (70 : 30 by weight), tertiary dodecyl mercaptan, potassium oleate and uranyl nitrate. The efficiency of the polymerization is compared with that using continuous illumination, efficiency being expressed as the ratio of polymerization rate to amount of light received. Suspension polymerization is also referred to.