Investigation of the Nematic-Isotropic Biphase in Thermotropic Main Chain Polymers. Homogeneity of the Pure Isotropic and Nematic Phases. Part III: NMR Study

Abstract

Nematic fraction f_N and biphase width are measured by combination of broad line PMR and DMR experiments and the data compared with microscopy and DSC results. Time dependence of f_N was monitored isothermally. Preliminary data suggest that: i) equilibrium distribution of chain lengths between I and N components is established rapidly; ii) supercooling at the I/N transition is of thermo-dynamic rather than kinetic origin. The DMR spectrum of PAAd14 is used to probe heterogeneity and isothermal evolution of molecular morphology in the pure N phase (model system of small molecules and polymers). Dynamics of homogenization of the N phase on the molecular level is extremely slow under normal laboratory conditions.