Copolymerization of styrene and methacrylic acid in concentrated emulsions

Copolymerization of styrene and methacrylic acid was carried out by the concentrated emulsion polymerization method, using sodium dodecylsulfate and AIBN as emulsifier and initiator, respectively. Compared to conventional emulsion polymerization, a much smaller amount of water (5–25 vol %) is employed as the continuous phase and thus the loss of methacrylic acid, which is very soluble in water, is minimized. The concentrated emulsion, which has the appearance of a gel, was prepared at room temperature, and was polymerized at 40°C. The size of copolymer latexes is affected by the internal phase ratio, and was in the range of 0.2–0.3 μm in diameter. Potentiometric titration was used to determine the surface density of the carboxylic groups of the copolymer latexes and its dependence on the feed molar ratio of methyacrylic acid to styrene. NMR and IR spectroscopies have been employed to determined the composition of the copolymer latexes.