Influence of the reference temperature on the orientation and relaxation of miscible polystyrene/poly(vinyl methyl ether) blends

The deformation and relaxation behavior of polymers depends heavily on temperature. In miscible polystyrene/poly(vinyl methyl ether) (PS/PVME) blends, which possess a broad glass transition region, polarization modulation infrared linear dichroism (PM-IRLD) measurements show that when the mean glass transition temperature (T-g) is used as the reference temperature, the orientation and relaxation of orientation of PS in the blends depend significantly on the composition. In contrast, similar values are obtained for blends containing between 40 and 100% PS when the end of the glass transition region (T-gf) is used as the reference temperature. Physical aging experiments made by differential scanning calorimetry indicate that T-gf can be associated with the highest temperature at which enthalpic relaxation occurs, above the mean T-g of the blend. Both series of results have been analyzed, first, by considering the presence of concentration fluctuations in the miscible blends and, second, in the framework of the Lodge-McLeish model.