Melt rheology of poly(ethylene terephthalate), polyarylate, and their blends

Rheological properties of two polyesters; poly(ethylene terephthalate) (PET) and bisphenol A‐50/50 isophthalic/terephthalic acid based polyarylate (PAR), and their 85/15, 50/50, and 30/70 (PET/PAR) blends were investigated using a RDS rheometer, 290–310°C. Measurements included complex viscosity and modulus. Activation energy for flow and relaxation spectrum were subsequently calculated. Results indicated that PET/PAR blends are rheologically incompatible, i.e., zero‐shear viscosities of the blends showed a negative deviation from the averages of the two homopolymers with a sharp minimum at 85/15 composition. The relaxation spectrum for 85/15 blend also showed a relaxation plateau, a characteristic of rigid particle suspension. The morphology of the polymer blends was examined from cryogenically fractured and etched surface using a scanning electron microscopy (SEM). Morphological observation indicated that PAR‐rich phases, order of 0.1μm, were finely dispersed in PET phase for 85/15 blend, whereas the dispersion of PET phase in PAR‐rich phase was in spherical form, order of 0.5μm in diameter, for the 50/50 blend.