Two mechanisms of liquid-liquid phase separation in polymer solutions are possible: nucleation and growth of one of the equilibrium phases, and decomposition by a spinodal mechanism. The conditions for and characteristics of both mechanisms are discussed. By combining a number of observations on phase separation in concentrated solutions of poly(2,6-dimethyl-1,4-phenylene ether) and of an ethylene — vinyl acetate copolymer in caprolactam, it becomes clear that a spinodal mechanism is operative at the onset of the separation process. In later stages the flow properties of the concentrated polymer phase determine the final state of the separated mixture.
Smolders, C. A., van Aartsen, J. J., & Steenbergen, A. (1971). Liquid-liquid phase separation in concentrated solutions of non-crystallizable polymers by spinodal decomposition. Kolloid-Zeitschrift und Zeitschrift für Polymere, 243(1), 14-20. https://doi.org/10.1007/BF01500609