THERMOREVERSIBLE SUPRAMOLECULAR NETWORKS WITH POLYMERIC PROPERTIES

Hydrogen bonding between carboxylic acids and pyridines can be used as a means of chain extension. However, the reversibility of hydrogen bo nd formation does not allow the chain-extended structure to be fixed, and a temperature-dependent chain length results. Complexation between a tetrapyridyl species and a diacid is shown to counteract the revers ibility of the hydrogen bonding. These complexes form thermoreversible three-dimensional supramolecular networks which have properties typic al of low molar mass materials at high temperatures but polymeric prop erties at low temperatures. The complexes exhibited a glass transition and could form fibers from the melt yet exhibited a low-viscosity iso tropic liquid at elevated temperatures. Atypically, a complex incorpor ating a 2,2',6,6'-tetrasubstituted biphenyl moiety was found to be liq uid crystalline.