Thermodynamic interactions in polydiene/polyolefin blends composed of 1,2-polybutadiene (1,2-PBD) and fully saturated (with deuterium) 1,2-PBD were explored with small-angle neutron scattering (SANS). Two methods were employed to extract the temperature dependence of the Flory− Huggins interaction parameter, χ, from SANS data obtained in the single-phase region. First, Zimm analysis was conducted employing data obtained at low scattering angles, providing a model-independent method of characterizing χ. Next, the random phase approximation was fit to the full angle-dependent absolute scattering intensity. The χ parameter for 1,2-PBD/ saturated 1,2-PBD was found to be large in magnitude at low temperatures and exhibited a strong temperature dependence. The experimentally measured χ, at high temperatures, was in agreement with predictions of solubility parameter theory based on PVT properties of the individual components. The large and strongly temperature-dependent χ parameter of the 1,2-PBD/saturated 1,2-PBD mixture is an attractive feature enabling facile material processing and is in stark contrast to behavior observed in more traditionally studied polyolefin/polyolefin and polydiene/polydiene pairs.