Mixtures of deuterated polyethylene oxide with hydrogenous polymethyl methacrylate and hydrogenous polyethylene oxide with deuterated polymethyl methacrylate have been investigated using small angle neutron scattering. The range of temperatures used was 423-473 K and the volume fraction of polyethylene oxide in the mixtures varied from ca. 0.1 to ca. 0.27. Values of the effective interaction parameter (chi(eff)) were obtained using the incompressible random phase approximation. Both temperature dependence and composition dependence were noted in the values of chi(eff). The temperature dependence observed was compared with that predicted by equation of state theory. A notable feature of the composition dependence of chi(eff) was the change in behaviour as temperature increased. Changes in the excess volume of mixing have been cited 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 independent interaction parameter have been obtained.