Self-assembly of taper-shaped monoesters of oligo(ethylene oxide) with 3,4,5-tris(p-dodecyloxybenzyloxy)benzoic acid and of their polymethacrylates into tubular supramolecular architectures displaying a columnar mesophase

Abstract

The taper-shaped monoesters of mono-3a, di-3c, tri-3d, and tetra-3f ethylene glycol with 3,4,5-tris(p-dodecyloxybenzyloxy)benzoic acid 1 and their corresponding polymethacrylates, 6a, b, c and d, respectively, self-assemble into a tubular supramolecular architecture displaying an enantiotropic columnar hexagonal (Φh) mesophase. Characterization of this supramolecular architecture by a combination of differential scanning calorimetry, wide- and small-angle X-ray scattering, thermal optical polarized microscopy, and molecular modelling suggests a model in which the stratum of the column is formed by in between 3.9 and 5.4 molecules of 3 or 4.5 and 5.9 repeat units of 6 with their oligo(oxyethylenic) segments melted and segregated in the centre of the column and their melted alkyl tails radiating towards the columns periphery. 2-(2-Methoxyethyl) 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate 3b(the model compound of 3a in which the hydroxy group has been replaced by a methoxy group) is only crystalline, while bis(2-{2-[3,4,5-tris(p-dodecyloxybenzyloxy)benzoyloxy]ethoxy}ethyl) ether 3g(which is the dimer of 3c) displays a monotropic Φh phase. These results support that endo-recognition by H-bonding of the oligo(oxyethylenic)receptor of 3 and exo-recognition provided by the tapered 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate fragment of 3(most probably functioning by hydrophobic–hydrophobic interactions) provide the driving force for the self-assembly of this tubular supramolecular architecture. In the case of the supramolecular architectures derived from 6, the H-bonding interaction is replaced by the poly(methacrylate) backbone which leads to a Φh mesophase that undergoes isotropization at temperatures that are 40 °C higher than those of 3. The channel penetrating the middle of the supramolecular cylinders derived from both 3 and 6 dissolves alkali-metal triflates and the ionic interaction generated by the dissolved ion-pairs enhances the thermal stability of their Φh phase. These results allowed for the first time a comparison between a ‘molecular’ polymer backbone effect (polymethacrylate) and a 'supramolecular' polymer backbone effect (generated by way of H-bonding and ionic interactions) to be made.