Phase behavior of the polybutadiene–polystyrene diblock copolymer with the addition of the nonselective solvent dichlorobenzene in temperature and pressure fields

Thermal composition fluctuations were measured in a polybutadiene–polystyrene diblock copolymer with small-angle neutron scattering as a function of the temperature, pressure, and solvent content. The solvent was dichlorobenzene. In particular, we determined the phase diagram, the Flory–Huggins parameter, and the Ginzburg parameter. The two latter parameters were determined in terms of a theory by Fredrickson and Helfand from the susceptibility at an elevated temperature in the disordered regime. These parameters showed an overall linear decrease with pressure and a minimum at a 10% solvent content. The ordering temperature could be sufficiently well described by the theory of concentrated solutions. These results were consistent with corresponding experiments on a polybutadiene–polystyrene blend, for which the compensation of the free volume was observed by the solvent molecules. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3179–3190, 2004