Synthesis and stereochemistry of isomeric methacrylic polymers derived from 4- and 5-aminosalicylic acids

The paper describes the direct synthesis of methacrylamide derivatives of 4-aminosalicylic acid (2-hydroxy-4-N-methacrylamidobenzoic acid, 4-HMA) and 5-aminosalicylic acid (2-hydroxy-5-N-methacrylamidobenzoic acid, 5-HMA). The monomers obtained present phenolic -OH and carboxylic functional groups in different positions of the side aromatic ring with respect to the methacrylamide group. This structural difference affects slightly the stereochemical structure of the polymers prepared by free radical polymerization at 50 sigma C. From a stereochemical point of view, the polymers are syndiotactic predominantly, with isotacticity parameters sigma=0.17 for poly(4-HMA) and sigma=0.20 for poly(5-HMA), and a Bernoullian distribution. The stereochemical configuration of polymers was analysed in terms of triads and pentads based on the C-13 nuclear magnetic resonance signals of the alpha-CH3, quaternary carbon and amide carbonyl carbon of the polymers. Differential scanning calorimetry gave values for glass transition temperature of 504 K for poly(4-HMA) and 534 K for poly(5-HMA), the difference being explained in terms of the inter- and intramolecular interactions of the polar -OH and -COOH side groups through hydrogen bonding as indicated by Fourier transform infra-red spectroscopy. (C) 1997 Elsevier Science Ltd.