Dielectric relaxation studies of miscible polycarbonate/polyester blends

Blends of bisphenol-A polycarbonate and a thermoplastic polyester (Kodar) a re miscible as shown by single DSC and DMTA glass transition temperatures a t all compositions. Blends of polycarbonate and Kodar also display a strong , single dielectric alpha -relaxation. Conclusions regarding the molecular nature of the blends, the state of mixing and molecular cooperativity can b e made by both quantitative and semi-empirical analysis of dielectric relax ation data. There is an increased broadening of the loss spectra on blendin g as determined by both Havriliak-Negami (HN) and Kohlrausch-Williams-Watts (KWW) fits to the dielectric data, and by analysis of the DMTA loss peaks. An increase of the relaxation time on blending is attributed to the temper ature of measurement being below the glass transition of the rigid PC-rich component of the blends and that this is likely to have an effect because o f micro-heterogeneity in the blends. Local regions of composition rich in K odar or polycarbonate exist in these blends and this allows the molecular m otion of the PC molecules to dominate the relaxation behaviour of the blend s. Concentration fluctuation is thus the dominant feature controlling the d ielectric response in these miscible, amorphous blends. (C) 2001 Elsevier S cience Ltd. All rights reserved.