MOLECULAR MOBILITY IN STYRENE-CO-METHACRYLIC ACID RANDOM COPOLYMERS FROM 100-K TO 450-K

Molecular mobility of both the polystyrene homopolymer and a series of styrene- co-methacrylic acid copolymers with various amounts of methacrylic acid is analyzed in the temperature range from 100 to 450 K, by high-resolution dynamic mechanical spectrometry, IR, and differential scanning calorimetry. Isochronal spectrometry exhibits for polystyrene homopolymer two relaxations, the beta and alpha relaxations, with increasing temperature. Styrene-co-methacrylic acid copolymers exhibit three mechanical relaxations, the gamma, beta, and alpha relaxations, from 100 to 450 K. These relaxations could be related to the progressive occurring of motions of the side groups and of the backbone chains when increasing the temperature. This could be due to the progressive breakdown of hydrogen bonds, which could show a somewhat wide range of magnitude. Furthermore, the decreasing of the magnitude of the a relaxation with increasing methacrylic acid content could suggest the presence of a stable network of chemical cross-links induced by the presence of anhydride so that molecular mobility could be partially inhibited above T(g). The remaining of a fluctuation network of hydrogen bonds (labile contacts) above T(g) could also emphasize the decrease in molecular mobility.