COIL AND MELT COMPRESSIBILITY OF POLYMER BLENDS STUDIED BY SANS AND PVT EXPERIMENTS

The average radius of gyration R(g) for the isotopic blend deuteropoly styrene/polystyrene (d-PS/PS) and for the blends deuteriopolystyrene/p oly(vinyl methyl ether) (d-PS/PVME) and deuteropolystyrene/poly(phenyl methylsiloxane) (d-PS/PPMS) has been measured by SANS experiments as a function of temperature (T) and pressure (p) up to 1.2 kbar. Furtherm ore, the specific volume as a function of p and T has been measured. T he resulting compressibilities beta(v) = -(1/V)(partial derivative V/p artial derivative p) and the compressibility of the radius of gyration , beta R(g) = -(3/R(g))(partial derivative R(g)/partial derivative p), were compared. For d-PS/PS the following were found: (i) For T > T-g (T-g = glass temperature) R(g) changes with pressure less than the mac roscopic sample dimensions (beta R(g) < beta(v))) whereas beta R(g) de creases with increasing temperature. (ii) At T-g geometrical affinity is approached (beta R(g) approximate to beta(v)) (iii) Below T-g there is still an increase of the ratio between beta R(g) and beta(v). This implies that in the glassy regime the polymer chain seems still to be mobile on a ''local scale. Thus, in general, it is concluded that the ''matrix effect'' in the chain is relatively small both above and bel ow T-g. The value of the temperature coefficient kappa = partial deriv ative ln(R(g)(2))/partial derivative T < 0 is consistent with detailed calculations of Yoon et al. For the other blends, where the temperatu res are far above T-g, the compressibilities beta(v) and beta R(g) dif fer strongly and the change of their values with temperature is small.