Alkaline Hydrolysis of Styrene-Acrylonitrile Copolymers

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Abstract
Styrene-acrylonitrile copolymers of different compositions have been hydrolyzed by concentrated potassium hydroxide in dioxane solutions as well as in ethanol and aqueous suspensions. The reaction rate was followed by the amount of liberated ammonia which was absorbed in 0.1 N H2 S04, thus resulting in pH changes. With a tenfold excess of KOH, first-order hydrolysis rate constants were obtained. A plot of the conversion of nitrile groups versus time plot follows the familiar pattern. The hydrolysis rate decreased greatly as the acrylonitrile content in the copolymer decreased. The reaction rates decreased in the order dioxane > ethanol > water. Compared to the statistical samples, the alternating SAN copolymer showed the highest resistance toward hydrolysis. The relation between the distribution of triads of the repeating units in the copolymer and the hydrolysis rate constants demonstrated the dominant influence of the structure of the copolymer on the hydrolysis rate.