Process control by surface tension measurement

摘要

Polymer latices are formed by conducting an emulsion polymerization reaction of the monomer, wherein a sample of reaction mixture is continuously withdrawn, changes in its surface tension are sensed by measuring the maximum pressure required to blow disciete bubbles in the sample and surface-active agent is added to the reaction mixture to maintain its surface tension at a predetermined value. Specified monomers are styrene, alpha-methyl styrene, divinyl benzene, acrylonitrile, butadiene, isoprene, vinyl chloride, vinylidene chloride, vinyl acetate. acrylic and methacrylic acids, ethyl acrylate and methyl methacrylate. In examples, (1) styrene was polymerized in presence of a tertiary mercaptan potassium persulphate and potassium oleate; (2) styrene/butadiene were copolymerized in presence of the ingredients of example (1) and additionally potassium hydroxide and sodium bisulphite; (3) butadiene was polymerized in presence of the ingredients of example (2); (4) methacrylic acid/styrene/butadiene were copolymerized in presence of a tertiary mercaptan, potassium persulphate, sodium bisulphite, ethylenediaminetetraacetic acid and an alkylbenzene sodium sulphonate; these reactions were initiated in absence of surface-active agent, which was added in accordance with the invention. In general, the surface-active agent may be an aqueous, alcoholic or other solution of a soap such as an alkali or alkali metal salt of e.g. lauric, palmitic, stearic, oleic or a rosin acid, or a solution of synthetic detergent such as sodium dodecyl benzene sulphonate or sodium lauryl sulphate, or a non-ionic surfactant. U.S.A. Specification 2,579,908 is referred to.ALSO:A method of controlling the surface tension of a liquid reaction mass whose surface tension tends to increase during reaction, comprises continuously withdrawing a sample of liquid, sensing changes in the surface tension of the sample by measuring the maximum pressure required to blow discrete bubbles therein and adding a surface-active agent to the reaction mass so as to maintain its surface tension at a predetermined value. The method is especially applicable to the polymerization of an aqueous emulsion of a monomer to form a polymer latex (see Division C3). An automatic apparatus is described. U.S.A. Specification 2,579,908 is referred to.