Laterally substituted dicarboxylic acids and their bispyridyl complexes: Main-chain association polymers
The design of laterally substituted dicarboxylic acids and dicarboxylic acid/bispyridyl adducts that display glass transitions and form fibers has been achieved. Both of these characteristics are found in conventional covalently bonded polymers, which leads us to believe that there is effective chain-extension within our association polymers. The dicarboxylic acids with larger substituents (i.e. nitro ( D4 ), bromo (D5 ), phenyl (D10 )), as well as those possessing two substituents per aromatic ring (i.e. methoxy (D11 ), methyl (D13 ), chloro (D14 )) readily form fibers and all have glass transitions. The lateral substituents are effective at retarding crystallization, which allows examination of the material at low temperatures, for the hydrogen-bonds are most effective at low temperatures. Therefore our association polymer chains are expected to be longer at low temperatures and shorter at higher temperatures. The complexation of bispyridyls with our acids provides a stronger hydrogen bond as well as mesogenic behavior. The directional character of the stronger hydrogen bond coupled with the directional ordering of the mesophase, enhances the polymer properties of our molecules.