Conformational motions in immiscible blends of polycarbonate and styrene-acrylonitrile copolymers

Blends of commercial bisphenol-A-polycarbonate and styrene-acrylonitrile copolymers were prepared by precipitation in ethanol from the solution in methylene chloride in order to eliminate the low molecular weight substances contained in the commercial polymers, specially the oligomers contained in commercial SAN copolymers. Two glass transitions appear in the DSC thermograms of the blend at the same temperatures as in the pure components which, in principle, indicates that the blend consists of two phases formed by pure PC and pure SAN. In order to detect small changes in the glass transition process that could be indicative of different mobility of the polymer chains in the blend with respect to the pure polymers, blends of different compositions were subjected to different thermal treatments that included annealing at temperatures below both glass transitions, and then the DSC thermograms were recorded. A broadening in the peaks shown by the c_p(T) curves measured on annealed samples in the zone of the PC transition is detected while no significant differences are shown by the glass transition of the SAN phase of the blend with respect to pure SAN copolymer. Dielectric relaxation experiments in the frequency domain (from 100 to 3·10⁶Hz) were carried out on the blends. The dielectric relaxation spectrum in the zone of the SAN main relaxation process was fitted with the stretched exponential equation showing no significant differences between the blends and the pure SAN copolymer. The region of the main relaxation process of PC was not analyzed due to the small polar activity of PC and the overlapping with the relaxation of the SAN phase.