Temperature dependence of the interaction parameter of polystyrene and poly(methyl methacrylate)

The Flory--Huggins interaction parameter, chi , has been determined for polystyrene, PS, and poly(methyl methacrylate), PMMA, by measuring the small-angle neutron scattering, SANS, from P(S-b-MMA), symmetric, diblock copolymers above the microphase separation temperature. The SANS profile can be well described by the correlation hole scattering from which chi is easily obtained. Measurements as a function of temperature yield chi = (0.028 plus /minus 0.002) + (3.9 plus/minus 0.06)/T where T is the absolute temperature. These results show that the entropic contribution of chi is much greater than the enthalpic contribution and that the temperature dependence of chi is weak. . 36 ref.--AA