Broadband Dielectric Spectroscopy for Poly (methyl methacrylate)/Poly (alpha-methyl styrene-co-acrylonitrile) Blend

摘要

Blends of poly (methyl methacrylate), PMMA, and Poly (alpha-methyl styrene-co-acrylonitrile), PalphaMSAN, random copolymer have been studied by broadband dielectric relaxation spectroscopy and differential scaning calorimenter (DSC). The dielectric measurements were carried out over a wide range of frequence (10~(-1) to 10~6 Hz)and temperature (30-155 deg C). The molecualr dynamics of the glass relaxation process, alpha-process, was investigated as functions of composition, frequency and temperature. It has been found that, only one common alpha-relaxation process has been observed for all measured samples, its dynamics and broadness were found to be composition dependent. The existence of only one common alpha-relaxation process located at a temperature range between of the pure polymer components was also confirmed by measuring the glass transition temperatures of the blends. T_gS, calorimetrically using DSC and dielectrically from the activation curves of the alpha-relaxation processes of the blends. The T_gs of the blends were found to follow Fox-equation. The composition dependence of hte dielectric relaxation strength, DELTAepsion has been also examined for alpha and beta-relaxation processes, In addition, the blending was found to have no effect on the kinetics and broadness of the beta-relaation processes of the PMMA, indicating that blending does not cahnge the local environment of each component in the blend. This also led to in turn that the mixing of the two polymer components should take place on a structure level bigger than the segmental level to keep the local environmental unchanged and small enough to have the same volume as the cooperative dipoles, which are related to the single T_g of the miscible blend.