Low‐temperature rubber: Emulsion polymerization in a salt antifreeze system

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Abstract
Butadiene‐styrene copolymers have been prepared at subfreezing temperatures by means of redox recipes employing inorganic salts as freezing point depressants. Specific salt‐emulsifier combinations are required for optimum rates of polymerizations. With a sufficient amount of the inorganic salt to lower the freezing point of water 10°C., the sodium chloride–potassium caprylate combination resulted in a 60% conversion in 4.6 hours, the calcium chloride–sodium hexyl sulfate combination resulted in a 41% conversion in 24 hours, and the calcium chloride–alkyl aryl polyether alcohol combination resulted in a 58% conversion in 18.5 hours.Low molecular weight mercaptans such astert‐butyl mercaptan can be employed as practical modifiers for this recipe.Certain of the physical properties of the salt antifreeze copolymers prepared at −10°C. are superior to those of copolymers prepared at the same temperature by means of conventional recipes. The ease of processing and the heat‐aged properties are exceptional. One copolymer after 24 hours of aging at 100°C. withstood 118,000 flexures before a puncture increased to one inch in length at 99°C. The superiority of the product is attributed to the precipitation of the copolymer during the course of the polymerization.