Quantitative determination of carboxyl endgroups in vinyl polymers by the dye-interaction method

Abstract

The possibility of quantitative estimation of carboxyl groups in polymers by the dyeinteraction method developed in this laboratory has been investigated. The benzene extract of rhodamine 6Gx from a buffer of pH 10 under specified conditions has been used as the reagent. The estimation has been made by colorimetric measurement at 515 mμ of the color developed by mixing a solution of the polymer in benzene with the reagent. Copolymers of styrene (or methyl methacrylate of vinyl acetate) with acrylic acid, methacrylic acid, crotonic acid, itaconic acid, or maleic anhydride at varying M₁:M₂ ratios in the 100:1 composition range have been prepared, and the monomer reactivity ratio r₁ (which under such conditions becomes equal to the ratio of the mole-per cent of carboxyl in the feed to that in the copolymer) has been determined. The result agrees fairly well with the value of r₁ reported in the literature. This indicates that the proposed method is capable of estimating fairly accurately the carboxyl groups or endgroups present in a polymer chain.