DYNAMIC-MECHANICAL STUDY OF THE DYNAMICS OF POLYMER BLENDS NEAR THE GLASS-TRANSITION

Poly(methyl acrylate) (PMA) and its blends with poly(4-hydroxystyrene) and a poly(4-hydroxy-co-4-methoxystyrene) have been studied by dynami c-mechanical spectroscopy at temperatures; close to the calorimetric g lass transition temperature T-g and frequencies between 0.3 and 30 Hz. The results for the imaginary part of the elastic modulus lead to bro ad master curves, which width increases with the content of the concen tration of the second polymer. Even though the results can be describe d reasonably well using a Kohlrausch-Williams-Watts relaxation functio n, rather low values of the stretching parameter beta are necessary in order to obtain good agreement with the experimental data. The Havril iak-Negami relaxation function leads to slightly worse agreement with experiment. The fragility parameter of the blends decreases with the c oncentration of PMA. The qualitative trend of the results may be inter preted in terms of the existence of concentration fluctuations in the blends.