Polyamide networks with stiff ‘liquid-crystalline’ segments and trifurcated flexible junctions

Abstract

The preparation of a novel family of polyamide network gels is described. In these networks, the segments are stiff and longer than the critical axial ratio for mesomorphic behaviour. The junctions are trifurcated and flexible. The gels were prepared at 10% network concentration. They are intensely birefringent in the relaxed nascent state, unlike fully rigid or flexible network gels. Upon swelling in N, N-dimethylacetamide (DMAc) to equilibrium, the gels lose their birefringence, which is recovered when the equilibrated gels are heated to less than 120°C and then cooled. The birefringence of the present gels is clearly associated with the coexistence in them of both long, stiff mesogenic segments and flexible trifurcated junctions. X-ray diffraction studies reveal the gelled networks to be fully amorphous. Thermal studies by differential scanning calorimetry indicate very strong attractive interactions between the polyamide networks and DMAc solvent, manifested by pronounced solvent retention in the gels at high temperatures and substantial lowering of both freezing and melting points of the DMAc in the gels relative to its transitions in the bulk.