Polymers and thermodynamics

Classic thermodynamic equilibrium considerations, supported by simple molecular models, may lead to useful predictions about phase relationships in partially miscible systems that contain polymers. How quantitative the prediction is depends on the amount of experimental information, as well as, on the complexity of the system. The solubility parameter and group contribution approaches present the first !eve! and allow a qualitative judgement whether a system is miscible or not. On this level, the entropy of mixing is not considered though it is higly important. A second, higher level of prediction is supplied by the Flory-Huggins-Staverman equation which permits estimations of the temperature and chain length dependence on the location of miscibility gaps. On this level the concentration ranges of partial miscibility are not well covered. Taking account of the ever present disparity in size and shape between molecules and repeat units improves the situation considerably and represents a third level of prediction. On this level the influence of pressure can reasonably accurately be dealt with. If predictions of a high precision are required, the present-day theory fails, even in the simple case of a linear, apolar homopolymer solution. Extensive measurements then remain needed to determine the many empirical and theoretical parameters. Predictions on such a high level have a more than academic value, since they may supply better mathematical frameworks to be applied in less demanding calculations.