We seek to investigate the non-equilibrium phenomena of a model polymer mixture by time-solved SANS and temperature jump experiments within (a) one-phase region and (b) one to two-phase region. The former will determine the q-dependent rate of growth (or decay) of concentration fluctuations between stable states while the latter yields chi parameters from the two-phase region, as well as a Cahn-Hilliard mobility parameter M. Such mutual diffusion coefficients will be directly comparable with interdiffusion FRES measurements (Kramer) and resolve a conflict between apparent thermodynamic interaction and (model-dependent) diffusion parameters in polymers. Mixture TMPC/PSd is chosen as model system for this study.