Structure Development in Reactive Polycarbonate‐Poly(Ethylene Terephthalate) Melt Blends

Abstract

A series of 50:50 polycarbonate‐poly(ethylene terephthalate) (PC‐PET) blends were formed via reactive melt blending in a torque rheometer at 270°C. The degree of interfacial transesterification between the two homopolymers was promoted by the incorporation of an alkyl titanium catalyst during melt blending. The resultant materials were characterized using differential scanning calorimetry (DSC), small‐angle light scattering (SALS), Fourier‐transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Multicycle DSC showed the uncatalyzed (0 T) blend to exhibit significant reactivity after four consecutive heat‐cool‐heat cycles between 50 and 280°C. The effect of interfacial transesterification on the melt morphology of the 0 T blend was studied using SALS. As transesterification proceeded, the domain size within the blend melt was observed to drop from ∼50 μm to ∼35 μm over a period of 120 s. The range of domain sizes measured by SALS after 120 s showed good agreement with values of domain thicknesses measured for co‐continuous PC‐rich and PET‐rich phases from SEM and TEM micrographs. The DSC, FTIR, and dynamic mechanical thermal analysis (DMTA) studies of 0 T and blends containing up to 150 ppm added alkyl‐titanium catalyst indicated that only relatively low levels of interfacial transesterification occurred during melt blending, although the level did increase with catalyst addition. The SALS, SEM, and TEM showed that the increased level of interfacial reaction changed the distribution of domain sizes in the blends and that a co‐continuous morphology persisted. In contrast, addition of 200 ppm catalyst resulted in a significant increase in the degree of transesterification and the formation of an amorphous, single‐phase material. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.