Fundamental importance of the diluent complete dissolution curve in phase diagrams for systems of polymer with low molecular compound

To construct phase diagrams for systems containing semicrystalline polymer with low molecular substance, such as an organic liquid or a solid matter, appears to be the first step in developing and producing polymeric films, powders and membranes.

There are several available methods of receiving data for phase diagram construction. One of the traditional techniques, the so-called differential scanning calorimetry method (DSC), is widely used in most of binary polymeric systems investigations. The method being fast and precise, however, it identifies processes that accompanied heat absorption/generation or changes of heat capacity only.

As the dissolution process is gradual, DSC fails to provide data about I/III border lines. Therefore, a substantial difference between the phase diagram obtained by DSC method and the complete phase diagram was observed (Fig. 1). '

Figure 1. Schematic interpretation of traditional (first) and complete (second) phase diagram of hypothetic binary system of semi crystalline polymer with low molecular liquid substance (polymer-good solvent).
Roman numerals represent different states. I corresponds to the two-phase system containing solid crystalline polymer with some diluent dissolved in its amorphous areas and liquid diluent. II demonstrates true solution of one component in another. III is one-phase microheterogeneous system, being the solution of diluent in amorphous areas of solid semicrystalline polymer.

Basko A.V.