Studies of the thermal stability of maleic anhydride co-polymers in aqueous solution

A study on the influence of the temperature of hydrolysis on molecular weig hts of poly(maleic anhydride-co-methyl vinyl ether) P(MAMVE) was carried ou t in aqueous solution. The self-association of polymer chains, due to hydro gen bonding between nonionized COOH groups and hydrophobic interactions, wa s decreased upon increasing temperature. Concomitant to that, scission of t he polymer chains was observed. From the molecular weights as obtained usin g a multiangle laser light scattering detector (MALLS), the main features o f the polymer degradation were determined: the degree of degradation, the s cission number, the activation energy (ca. 70 kJ/mol) and the rate constant (ca 10(-9)/s). The change in polymer conformation showed that the desaggre gation took place during the first 48 h at 100 degrees C; thereafter the de gradation mechanism became predominant. It was observed that the degradatio n process of P(MAMVE) was favoured for pH values below 7 and that the stabi lity of maleic anhydride copolymers was influenced by the chemical nature o f the co-monomers. The side-products originating from the degradation were methanol and carbon dioxide (CO2). During degradation in the solid state of the co-polymer under the anhydride form, CO? release occurred at 250 degre es C and no methanol was released. This last result confirmed that the degr adation in solution requires the presence of carboxylic acid moieties. (C) 1999 Elsevier Science Ltd. All rights reserved.