The free enthalpy correction parameter g in the Flory-Huggins equation for the Gibbs free enthalpy of mixing in polymer solutions is considered generally as a concentration- and temperature-independent parameter. It has been extended here with linear concentration- and temperature-dependent terms. With these parameters, six different types of cloudpoint curves can be predicted. Using the experimental cloudpoint curve for solutions of poly(2,6-dimethyl-1,4-phenylene oxide) in toluene up to about 70 per cent by weight of polymer, a set of g-parameters is obtained, accounting for concentration and temperature dependence. With the parameters thus obtained, the melting point curve has been calculated which agrees very well with the experimental melting points for this system.