Main-chain, thermotropic, liquid-crystalline, hydrogen-bonded polymers of 4,4′-bipyridyl with aliphatic dicarboxylic acids

A series of main-chain, thermotropic, liquid-crystalline (LC), hydrogen-bonded polymers or self-assembled structures based on 4,4'-bipyiidyl as a hydrogen-bond acceptor and aliphatic dicarboxylic acids, such as adipic and sebacic acids, as hydrogen-bond donors were prepared by a slow evaporation technique from a pyridine solution and were characterized for their thermotropic, LC properties with a number of experimental techniques. The homopolymer of 4,4'-bipyridyl with adipic acid exhibited high-order and low-order smectic phases, and that with sebacic acid exhibited only a high-order smectic phase. Like the homopolymer with adipic acid, the two copolymers of 4,4'-bipyxidyl with adipic and sebacic acids (75/25 and 25/75) also exhibited two types of smectic phases. In contrast, the copolymer of 4,4'-bipyridyl with adipic and sebacic acids (50/50), like the homopolymer with sebacic acid, exhibited only one high-order smectic phase. Each of them, including the copolymers, had a broad temperature range of LC phases (36-51degreesC). The effect of copolymerization for these hydrogen-bonded polymers on the thermotropic properties was examined. Generally, copolymerization increased the temperature range of LC phases for these polymers, as expected, with a larger decrease in the crystal-to-LC transition than in the LC-to-isotropic transition. Additionally, it neither suppressed the formation of smectic phases nor promoted the formation of a nematic phase in these hydrogen-bonded polymers, as usually observed in many thermotropic LC polymers. The thermal transitions for all of them, measured by differential scanning calorimetry, were well below their decomposition temperatures, as measured by thermogravimetric analysis, which were in the temperature range of 193-210degreesC. (C) 2003 Wiley Periodicals, Inc.