Wen-bing HU. Two Kinds of Judgement for Good Solvent and Poor Solvent of Polymers[J]. Polymer Bulletin, 2000,13(2):97-98,F3. DOI: 10.14028/j.cnki.1003-3726.2000.02.016.
There are two kinds of judgement to goodness of the solvent in polymer solutions. One is χ=1/2
from the free energy of Flory-Huggins mean-field calculation and the second Virial coefficient in the expansion of the osmotic pressure for dilution solution; another is χ=0
from the mixing heat. The former occurs in the current textbooks about polymer physics in China
but the author prefers the latter and gives his reasons.