Solubility of polymers

Polymers differ from low molecular weight compounds in a number of ways; among them are (i) the comparatively low thermal expansivities and compressibilities of their melts at higher temperatures, (ii) the frequent occurence of solidification to a glass instead of a crystal at low temperatures, and (iii) the fact that even chemically uniform polymer samples normally consist of a large number of species differing in molecular mass and architecture. The consequence of these peculiarities of polymers with respect to their solubility are discussed for the example of linear chain molecules. Firstly, the survey will review the experimental methods (some of which were specially developed for polymer solutions) for the determination of solubility limits and critical conditions. Then the general phenomena observed with systems containing high molecular weight material will be worked out and discussed theoretically. The main independent variables are: temperature, pressure, molar mass of the polymer and shear rate (for solubility in flowing systems). In addition, isotopic effects on the solubility will also be considered.