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

Abstract

A series of main-chain, thermotropic, liquid-crystalline (LC), hydrogen-bonded polymers or self-assembled structures based on 4,4Ј-bipyridyl 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 4,4Ј-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 4,4Ј-bipyridyl with adipic and sebacic acids (75/25 and 25/75) also exhibited two types of smectic phases. In contrast, the copolymer of 4,4Ј-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 -51°C). 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 193-210°C.

Supramolecular Liquid-Crystalline Polymer Organogel: Fabrication, Multiresponsiveness, and Holographic Switching Properties

“…Two additional peaks at 1927 and 2521 cm –1 appeared in the FTIR spectra of PM 11 AzPy–OA (1:1) compared with those of PM 11 AzPy, which can be assigned to the Fermi resonance bands and the vibration of hydroxyl groups, respectively . The peak at 930 cm –1 in the FTIR spectra of OA, corresponding to the out-of-plane O–H wagging vibration of the carboxylic acid dimers, disappeared completely in those of PM 11 AzPy–OA (1:1), strongly indicating the formation of hydrogen bonds between the carboxylic acid and the pyridyl group …”

Siloxane‐containing liquid‐crystalline supramolecular polymers: Preparation and study of thermotropic behavior

“…The self‐assembly of carboxylic acids as proton donors with pyridyl fragments as proton acceptors is most frequently used in the formation of hydrogen‐bonded structures 8. Such supramolecular polymers have been obtained and investigated, especially for liquid‐crystalline properties 8–13. It has been observed that hydrogen bonding in supramolecular polymers is enhanced by liquid crystallinity and phase separation 3.…”

“…8 Such supramolecular polymers have been obtained and investigated, especially for liquid-crystalline properties. [8][9][10][11][12][13] It has been observed that hydrogen bonding in supramolecular polymers is enhanced by liquid crystallinity and phase separation. 3 Siloxane-containing benzoic acids and bipyridine also form interesting supramolecular structures with cubic mesophases.…”

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

“…We also reported the preparation and characterization of chain-extended supramolecular polymers of 4,49-bipyridyl with adipic and/or sebacic acids, which exhibit thermotropic LC properties. They typically exhibit smectic phases, and even copolymers, unlike many other thermotropic LCPs, also exhibit smectic phases [48,49].…”

“…We note that the induction of liquid crystallinity via the H-bond is limited to a large extent to side chain LCPs [21,27,[51][52][53], but relatively few studies have been reported for main chain LCPs through the Main chain LC H-bonded polymers 843 secondary interactions of H-bonds [33,[41][42][43][44][45][46][47][48][49]54]. Therefore, it was of principal interest to study the thermotropic LC properties of new, chain-extended, supramolecular polymers that derive directly from these secondary interactions and to understand the structureproperty relationships of this novel class of polymers.…”