Synthesis of main‐chain hydrogen‐bonded supramolecular liquid crystalline complexes: The effects of spacer on thermal behavior of mesophase

Two series of difunctional proton acceptors, stilbazole derivatives 4a–c and 6a–c with different spacers, oligo(methylene) and oligo(ethylene glycol), respectively, were synthesized. Hydrogen‐bonded polymeric complexes 4/7 and 6/7 and trimeric complexes 4/82 and 6/82 (7 and 8 are aromatic dicarboxylic acids and monocarboxylic acids, respectively) were prepared, and their liquid crystallinity was examined. The effects of the spacer in 4, 6, and 7 and the terminal group in 8 on the thermal behaviors of hydrogen‐bonded complexes were investigated using differential scanning calorimetry and polarizing optical microscopy. X‐ray diffraction at elevated temperatures was used to verify liquid crystal phases. The study showed that the phase transition temperatures for isotropic to nematic (TI–Ns) of polymeric complexes 4/7 and 6/7 in general decreased with the increase in length of spacer in the corresponding proton donors 7. The increase in length of the proton acceptors 6 led to a drop of TI–Ns of the corresponding complexes 6/7; however, the TI–Ns of complexes 4/7 did not show any correlation with the spacer length in 4. In contrast, the increase in length of the terminal group in 8 resulted in a slight decrease in TI–Ns of trimeric complexes 4/82, but had a negligible effect on the TI–Ns of 6/82 because of the presence of the more flexible spacer in the proton acceptors 6. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4731–4743, 2005