Utilization of the oligomeric diglycidylether of bisphenol A epoxy in assessing equilibrium phase behaviour of polycarbonate/poly(methyl methacrylate) blends

Abstract

Abstract The long controversial nature of the equilibrium phase behaviour in the blend system of poly(methyl methacrylate) (PMMA) with bisphenol A polycarbonate (PC) was investigated by dissolving both polymers in an oligomeric epoxy, namely the diglycidylether of bisphenol A (DGEBA). Phase behaviour and morphology changes with temperature were examined by using differential scanning calorimetry (d.s.c.) and optical microscopy. Upon lowering the T g s of the PC/PMMA blends, thus enhancing the chain mobility by the plasticizing epoxy molecules, phase separation did take place in the blend with an accelerated rate at temperatures as low as 68°C. To our knowledge, this has never been reported previously in the literature. Consequently, the widely reported miscibility and lower critical solution temperature ( LCST ) in PC/ PMMA blends have to be carefully reinterpreted. Our results have suggested that the equilibrium behaviour of PC/PMMA blends is actually one of phase separation, with possibly only partial miscibility. In addition, this study has also showed that the single- T g , transparent blends above 240°C of the reported ‘upper critical solution temperature ( UCST )’ are actually not miscible but display microphase domains. A reinterpretation was provided based on these results.