SYNTHESIS AND STEREOCHEMISTRY OF ISOMERIC METHACRYLIC POLYMERS DERIVED FROM 4-AMINOSALICYLIC 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 a cid, 5-HMA). The monomers obtained present phenolic -OH and carboxylic functional groups in different positions of the side aromatic ring wi th respect to the methacrylamide group. This structural difference aff ects slightly the stereochemical structure of the polymers prepared by free radical polymerization at 50 sigma C. From a stereochemical poin t of view, the polymers are syndiotactic predominantly, with isotactic ity parameters sigma=0.17 for poly(4-HMA) and sigma=0.20 for poly(5-HM A), and a Bernoullian distribution. The stereochemical configuration o f polymers was analysed in terms of triads and pentads based on the C- 13 nuclear magnetic resonance signals of the alpha-CH3, quaternary car bon and amide carbonyl carbon of the polymers. Differential scanning c alorimetry gave values for glass transition temperature of 504 K for p oly(4-HMA) and 534 K for poly(5-HMA), the difference being explained i n terms of the inter- and intramolecular interactions of the polar -OH and -COOH side groups through hydrogen bonding as indicated by Fourie r transform infra-red spectroscopy. (C) 1997 Elsevier Science Ltd.