Phase behaviour and structure formation in solutions of vinyl polymers

The supramolecular structure formation in solutions of syndiotactic polystyrene is discussed from the viewpoint of the temperature-concentration behaviour of this system. The phase diagrams that result from these investigations localize the different temperature-concentration domains in which the β -phase (planar zigzag chain conformation) and the δ -phase (helix chain conformation) are formed. The study of these diagrams informs also on the relationship between the different phases and the nature of the supramolecular structure that is formed. The shape of the diagrams is characteristic of the formation of an incongruent melting compound ( δ -phase) between the polymer and the solvent. The formation of this compound at not to high polymer concentrations leads to the formation of thermoreversible gels. The solvent quality has a different influence on the stability of the β - and the ( δ -phase. An increase of the solvent quality lowers the melting point of the β -phase, but increases the stability of the ( δ -phase. The diagrams are interpreted on the basis of schematized equilibrium diagrams.