Abstract: The concept of volume fraction at chain-end is presented to overcome the mean-field approximation in Flory-Huggins(FH) theory. With the concept of interval-continuous chain introduced to replace multi-chains mathematically, some thermodynamical quantities can be written in path integral method. The entropy of polymer/solvent system is divided into two parts. Based on the conditions metioned above and the approximation that the interaction energy doesn′t affect the entropy of the system, a new theory of polymer solutions is built. The calculated FH interaction parameter and the spinodal curves with different molecular weights of PS are all quite well consistent with the experimental data, and much better than those of FH theory.

Key words: Volume fraction at chain-end, Path integral method, Polymer solution, Phase separation, FH interaction parameter