RHEOLOGY AND PHASE-BEHAVIOR OF BLENDS OF POLY(ETHYLENE OXIDE) WITH POLY(VINYL ACETATE) AND WITH POLY(VINYL ACETATE-RAN-ETHYLENE)

Abstract

The dynamic viscoelastic properties of blends of poly(ethylene oxide) (PEO) with poly(vinyl acetate) (PVAc) and with poly(vinyl acetate-ran-ethylene) (PVAE) were measured, using a cone-and-plate rheometer in the oscillatory shear mode. For the study, two grades of PEO, one with weight-average molecular weight M(w) = 20 000 (PEO20) and the other with M(w) = 100 000 (PEO100), were used. The PVAE used was found to be amorphous, as determined by differential scanning calorimetry, and it had M(w) = 12 600, as determined by gel permeation chromatography, and 73.4 wt% vinyl acetate, as determined by elemental analysis. It was found that the amorphous phase of the PEO20/PVAc blend system has one glass transition temperature T(g) over the entire range of blend compositions, whereas the amorphous phase of the PEO100/PVAc blend system has one T(g) for blend compositions up to 50 wt% PVAc, but two T(g) values for blends with greater amounts of PVAc. Melting-point depression measurements were conducted to determine the Flory interaction parameter chi to be: (a) -0.211 for PEO20/PVAc pair; (b) -0.069 for PEO100/PVAc pair; (c) -0.027 for PEO20/PVAE pair; and (d) -0.024 for PEO100/PVAE pair. Our experimental results show that plots of the logarithm of zero-shear viscosity versus blend composition at constant temperature exhibit negative deviations from linearity for the PEO20/PVAc blend system, but positive deviations from linearity for both PEO20/PVAE and PEO100/PVAE blend systems. These experimental observations are interpreted using a molecular viscoelasticity theory recently developed by Han and Kim.