Nearly monodisperse spherical domain morphology in polycarbonate/ poly(methylmethacrylate) blends following spinodal decomposition coupled with an interchange reaction

The morphological development in blends of bisphenol-A polycarbonate (PC) and poly(methylmethacrylate) (PMMA) blends during isothermal annealing above 200°C has been investigated where competition between liquid-liquid phase separation by spinodal decomposition and interchange reactions take place. Interchange reactions between PC and PMMA occurs at temperatures above 200°C and leads to the formation of in situ graft copolymers from an ester-ester interchange reaction. During spinodal decomposition, graft copolymers are produced mainly at the interface region between the interconnected microphase domains. Instead of the usual "coarsening" process which is characteristic of the late-stage of spinodal decomposition, the mixture exhibits nearly monodisperse spherical domains as revealed by optical microscopy. This phenomenon is further studied through extensive small angle light scattering measurements. Resonance peaks up to fourth order are noted, a rare observation. The result clearly demonstrates that graft copolymers are formed in situ and can act as very effective "surfactants" in polymer blends. Furthermore, an attempt is made to analyze the angular dependence of the scattering intensity from this morphology with the Percus-Yevick hard sphere liquid theory. These results are believed to be general and therefore applicable to a wide variety of blends containing one or more components capable of an interchange reaction.