Supramolecular Interactions in the Formation of Thermotropic Liquid Crystalline Polymers - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 128

Fig. 7 A selection of bis benzoic acids and bis pyridine derivatives which have been used
to access main-chain liquid crystalline polymers
by Hoogboom and Swager. Poly(phenylene ethynylene) derivatives (Fig. 8)
that were endcapped with the four-fold hydrogen-bonding ureidopyrimidi-
none (Upy) motif and containing pendent iptycene groups on every second
backbone aromatic ring were synthesized. The iptycene moieties had previ-
ously been shown by the same group to create a strong coupling between
a rigid polymer and the molecular director of nematic liquid crystals. When
such compounds were dissolved in the nematic solvent, 5CB, a strong en-
hancement of the dichrotic ratio as well as the apparent polymer conjugation
length were witnessed for the case of Upy-capped PPE when compared to
non-functionalized counterparts. Moreover, it was proven that the length of
the main chain supramolecular polymer has an effect on the dichroic ratio.
The addition of chain terminating mono-Upy compounds which result in the