The interaction of butadiene-styrene block copolyincis of different molecular architecture with tetrahydrofuran (THF) was studied by vapor pressure and light scattering experiments in the temperature range from 25 to 55 degrees C The thus obtained Flory-Huggins interaction parameters, chi, as a function of phi, the volume fraction of the polymers, were compared with that of the corresponding homopolymersim in the same solvent The results are very similar for all block copolymers (diblock, triblock and star-shaped, butadlene In the chi(phi) Curves of the homopolymers, which are always located center) and for all temperatures In contrast to they chi(phi) curves of the homopolymers, which are always located above their tangents, the dependencies for the block copolymers exhibit it maximum in the range of moderate polymer concentrations, where the heats of dilution are close to athermal ill the range of low phi values but become pronouncedly endoiliernial rot high phi values These Findings call be well modeled by all approach considering the phenomena of chain connectivity and conformational relaxation of polymers , If one accounts for the unfavorable interactions between the monomeric units of the different blocks