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 metha crylic 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 polystyren e homopolymer two relaxations, the beta and alpha relaxations, with in creasing temperature. Styrene-co-methacrylic acid copolymers exhibit t hree mechanical relaxations, the gamma, beta, and alpha relaxations, f rom 100 to 450 K. These relaxations could be related to the progressiv e occurring of motions of the side groups and of the backbone chains w hen increasing the temperature. This could be due to the progressive b reakdown of hydrogen bonds, which could show a somewhat wide range of magnitude. Furthermore, the decreasing of the magnitude of the a relax ation with increasing methacrylic acid content could suggest the prese nce of a stable network of chemical cross-links induced by the presenc e 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 mole cular mobility.