The polymer blend system of deuterated polystyrene (PS(D)) and a statistical copolymer poly(cyclohexyl acrylate-stat-n-butyl methacrylate) (P(CHA(1-x)-stat-nBMA(x))) was investigated by small-angle neutron scattering (SANS) and neutron reflectometry (NR). The Flory-Huggins-Staverman interaction parameter chi was determined as a function of temperature and copolymer composition in the one- and two-phase regions by SANS and NR, respectively. By a combination of both methods compatible and incompatible blends could be investigated. It is shown that theoretical treatments of the two regimes are consistent. The phase diagram is calculated where a snitching from an upper critical solution temperature to a lower critical temperature behavior is predicted.