ISOTOPIC LABELING AND COMPOSITION DEPENDENCE OF INTERACTION PARAMETERS IN POLYETHYLENE OXIDE POLYMETHYL METHACRYLATE BLENDS

Mixtures of deuterated polyethylene oxide with hydrogenous polymethyl methacrylate and hydrogenous polyethylene oxide with deuterated polyme thyl methacrylate have been investigated using small angle neutron sca ttering. The range of temperatures used was 423-473 K and the volume f raction of polyethylene oxide in the mixtures varied from ca. 0.1 to c a. 0.27. Values of the effective interaction parameter (chi(eff)) were obtained using the incompressible random phase approximation. Both te mperature dependence and composition dependence were noted in the valu es of chi(eff). The temperature dependence observed was compared with that predicted by equation of state theory. A notable feature of the c omposition dependence of chi(eff) was the change in behaviour as tempe rature increased. Changes in the excess volume of mixing have been cit ed as a possible source of this behaviour, but the currently available data do not allow us to confirm this. Using the relation between chi( eff) and a composition independent interaction parameter proposed from Monte Carlo simulations, approximate values of the composition indepe ndent interaction parameter have been obtained.