Blends of polybutadiene with different vinyl contents and polystyrene studied with small-angle neutron scattering in varying temperature and pressurefields

Blends of polybutadiene with three different vinyl contents and polystyrene were studied by small-angle neutron scattering as a function of temperatur e and pressure. The data were analyzed with a crossover function combining the universality classes of the 3D-Ising and the mean field behavior and th us yield the spinodal temperature T-S, the Ginzburg number Gi, and the crit ical amplitude C-MF. From these parameters the mean field Flory-Huggins int eraction parameter is calculated in terms of entropic and enthalpic contrib utions. The application of the theory of random copolymers delivers large e nthalpic and entropic contributions of the intramolecular interaction betwe en the 1,2- and 1,4-butadiene units. These numbers could not be confirmed f rom measurements of the corresponding intermolecular interaction contributi ons in an h-PB(1,2)/d-PB(1,4) blend, which thus leads to speculations about the equivalence of inter- and intramolecular interactions in random copoly mers. The Ginzburg number proved to be specific to the vinyl content and th us deviated from the universal behavior Gi proportional to V-1 predicted by deGennes. By our pressure experiments we find that the Clausius-Clapeyron equation suggests the phase boundary to be influenced by the Flory-Huggins parameter and the Ginzburg number.