Dynamic rheological analysis of a miscible blend showing strong interactions

The rheological behavior of miscible blends was studied through oscillatory shear measurements. Two miscible blends were selected to compare with athermal blending cases, i.e. the hydrogen bonding poly(4-vinyl phenol)/poly(ethylene oxide) (PVPh/PEO) blend and the weakly interacting polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide) (PS/PPO) blend. The homopolymers and the blends were characterized over a wide experimental window using the time-temperature superposition principle. The horizontal shift factor, a(T), does not vary appreciably with composition for PS/PPO, whereas a strong compositional dependence is observed for the PVPh/PEO blends. Additions of up to 30 wt% of PEO to PVPh produce only minor changes in the value of rubber plateau modulus (G(N)(0)), while G(N)(0) increases steadily after this concentration. The G(N)(0) values follow athermal blending models [J. Polym. Sci., Part B: Polym. Phys. 25 (1987) 2511; J. Polym. Sci., Part B: Polym. Phys. 26 (1988) 2329] in the case of PS/PPO but not of PVPh/PEO. Values of eta(0b) for PVPh/PEO blends were estimated from weighed relaxation spectra. The three measured parameters, aT, Go and 770 show a turning point around 20-30 wt% of PEO, which corresponds to a 41-54 mol% of PEO, in correlation with the previously reported observation of a maximum in the deformation-induced uniaxial orientation behavior of PEO component near this composition [Macromolecules 32 (1999) 8509]. (C) 2003 Elsevier Science Ltd. All rights reserved.