MISCIBILITY AND PHASE SEPARATION BEHAVIOR OF AMORPHOUS/AMORPHOUS POLYMER BLENDS

The substitution of deuterated polystyrene (PSD) for hydrogenated PS (PSH) in PS/PVME blends raised the LCST of the blend by about 40(DEGREES)C. This deuteration effect has been qualitatively interpreted by the larger percentage of negative excess volume of mixing for PSD/PVME relative to that of PSH/PVME. Both blends have the same glass transition temperature (T(,g)) for the same composition. Dynamic parameters--maximum scattering vector (q(,m)) and time (t) of spinodal decomposition for critical composition 30/70 wt% of PSD/PVME and PSH/PVME blends studied by light scattering are scaled to the reduced variables Q(,m) and (tau), respectively, in terms of the characteristic parameters--diffusion constant (D) and q(,m) (t = 0). Phase separation process is found to be the same for PSD/PVME, PSH/PVME and other systems such as metallic alloys, inorganic glasses and small molecule systems. Their exponent has the same value (1.0) according to the power-law approach. The phase separation kinetics for PSD/PVME is much faster than that for PSH/PVME with the same degree of superheating simply due to its lower viscosity and higher diffusion constant. The neutron cloud point was observed by the temperature scanning Small Angle Neutron Scattering (SANS) for PSD/PVME blends, which was in good agreement with light cloud point . Phase reversibility of the blends are also investigated. By employing the de Gennes\u27 scattering function for blends, the correlation length ((xi)), average statistical segment length ((\u27)b) and interaction parameter((chi)) were obtained as functions of temperature and composition from SANS measurements. The observed (\u27)b value was 7.7(ANGSTROM) consistent with the calculated value of 8.5(ANGSTROM) considering the polydispersity effect. The spinodal temperature was obtained by the correlation length approach. The critical exponents (nu) and (gamma) were close to 0.5 and 1.0, respectively, which implies that the blend can be described by the mean field theory. The composition dependence of (chi) was observed and explained in terms of Sanchez\u27s fluid lattice theory. Also, modified Noryl blends--PpMS/PPO and P(pMS-Co-St)/PPO have been found to be miscible from DSC measurements