Phase behaviour of blends of polyesters and polycarbonates

The phase behaviour of binary blends of polyesters and polycarbonates has been reviewed with reference to predictions of the enthalpic interaction, calculated using a binary interaction model, and with published information. Supplementary investigations of the mixing behaviour of additional blends are also reported and the results compared to model predictions. Calculations have been scaled using segmental interaction parameters derived from previous investigations of blends involving polyamides and copolyesteramides. By establishing boundary conditions for interactions in blends of polyesters and bisphenol A polycarbonate, the segmental interaction parameters involving carbonate segments have been estimated and found to be quantitatively similar to those involving the ester moiety. Results confirm that interactions in blends of polyesters and polycarbonate can be exothermic when certain compositional requirements are satisfied; however, the model predicts exclusively endothermic mixing for all binary polyester blends and that in these situations, miscibility occurs only when the entropic contribution to the free energy of mixing overwhelms the unfavourable interaction. Events that may moderate the mixing behaviour of blends, such as transesterification, have also been addressed. Exploratory projections are also presented for blends involving aliphatic polycarbonates and liquid crystalline polyesters. The results presented are broad in scope and exceptions to predictions are accounted for by considering the simplifications introduced to perform the analysis. (C) 1998 Elsevier Science Ltd. All rights reserved.