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

Blends of commercial bisphenol-A-polycarbonate and styrene-acrylonitrile co polymers were prepared by precipitation in ethanol from the solution in met hylene chloride in order to eliminate the low molecular weight substances c ontained in the commercial polymers, specially the oligomers contained in c ommercial SAN copolymers. Two glass transitions appear in the DSC thermogra ms of the blend at the same temperatures as in the pure components which, i n 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 chain s in the blend with respect to the pure polymers, blends of different compo sitions were subjected to different thermal treatments that included anneal ing at temperatures below both glass transitions, and then the DSC thermogr ams were recorded. A broadening in the peaks shown by the c(p)(T) curves me asured on annealed samples in the zone of the PC transition is detected whi le no significant differences are shown by the glass transition of the SAN phase of the blend with respect to pure SAN copolymer. Dielectric relaxatio n experiments in the frequency domain (from 100 to 3.10(6)Hz) were carried out on the blends. The dielectric relaxation spectrum in the zone of the SA N main relaxation process was fitted with the stretched exponential equatio n showing no significant differences between the blends and the pure SAN co polymer. The region of the main relaxation process of PC was not analyzed d ue to the small polar activity of PC and the overlapping with the relaxatio n of the SAN phase.