We have measured the small-angle neutron scattering from semidilute solutions of poly(vinyl methyl ether) in water and in methanol-water mixtures in a poor solvent regime. The binary and ternary duster integrals of the polymer segments were determined from the concentration dependence of the correlation length at various temperatures just below the lower critical solution temperature. We have calculated the contributions of the segment-segment interactions to the entropy and enthalpy from the measured temperature dependences of these interaction parameters and found that both quantities are positive and decrease with increasing methanol content. The implication of these findings is discussed.