Main chain, thermotropic, liquid crystalline, hydrogen-bonded polymers of 4,4′-bipyridyl with 4,4′-dicarboxy-α,ω-diphenoxyalkanes

A series of main chain, thermotropic, liquid crystalline (LC) hydrogen-bonded polymers based on 4,49-bipyridyl as a hydrogen bond acceptor and 4,4'-dicarboxy-alpha,omega-diphenoxyalkanes as hydrogen bond donors were prepared by a slow evaporation technique from a pyridine solution and characterized for their thermotropic LC properties using a variety of experimental techniques. The homopolymer of 4,4'-bipyridyl with 4,4'-dicarboxy-1,9-diphenoxynonane exhibited relatively low T-m at 205 degrees C and low T-i at 230 degrees C, giving an LC phase range of 25 degrees C. The other two homopolymers with 4,4'-dicarboxy-1,6-diphenoxyhexane and 4,4'-dicarboxy-1,9-diphenoxydecane exhibited relative low T-m values, above which each of them formed high-order smectic phases. With further heating at higher temperature they transformed into low-order smectic phases that persisted up to their decomposition temperatures. Several copolymers also had relatively low T-m values as well as low T-i values and, therefore, had a broad LC phase range (22-77 degrees C). All of the polymers including copolymers exhibited high-order and low-order smectic phases, since they developed usually mosaic and schlieren (or batonnets) textures. Generally, copolymerization increased the temperature range of the LC phases for these polymers. The thermal transitions of all of the polymers were well below their decomposition temperatures, which were in the ranges of 254-329 degrees C.