Broadband dielectric spectroscopy for poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) blend

Blends of poly(methyl methacrylate), PMMA, and Poly(α-methyl styrene-co-acrylonitrile), PαMSAN, random copolymer have been studied by broadband dielectric relaxation spectroscopy and differential scanning calorimeter (DSC). The dielectric measurements were carried out over a wide range of frequency (10^-1 to 10⁶ Hz) and temperature (30-155°C). The molecular dynamics of the glass relaxation process, α-process, was investigated as functions of composition, frequency and temperature. It has been found that, only one common α-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 α-relaxation process located at a temperature range between those of the pure polymer components was taking as a strong evidence for the miscibility of the blend over the entire range of composition. The miscibility 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 α-relaxation processes of the blends. The T_g of the blends were found to follow Fox-equation. The composition dependence of the dielectric relaxation strength, Δε has been also examined for α and β-relaxation processes. In addition, the blending was found to have no effect on the kinetics and broadness of the β-relaxation processes of the PMMA, indicating that blending does not change 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 environment of 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.