The phase transition of PSLG in the optically anisotropic state was studied in terms of the thermal behaviors examined by DTA, DSC and TGA.
A fraction of water in the solution containing PSLG of less than 48% freezed, whereas the rest water did not freeze. Water in the solution containing more than 48% PSLG did not freeze at all, indicating that the water is associated closely with PSLG molecule.
The structure of the solution of PSLG below 60% was regarded as a liquid crystal, and that of the solution above 70% was regarded as a crystal. These conclusions agreed closely with those obtained by X-ray analysis.
Phase diagrams were obtained referring to the PSLG concentration and the molecular weight. The anisotropic to isotropic transition temperature for the PSLG solution of below 60% was lower than 100°C, and the temperature for the solution of above 70% was higher than 200°C. The relationship between the transition temperature (
T) and degree of polymerization (
DP) of PSLG was represented by the following relation (1), where
K and
C are constant. Also the relationship between the transition concentration and the molecular weight of PSLG at 20°C agreed with Flory's prediction as, where
v*2 is the concentration in the volume fraction at which anisotropic phase appears, and
x is the axial ratio of PSLG helix.
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