SELF-ASSEMBLY OF TAPER-SHAPED MONOESTERS OF OLIGO(ETHYLENE OXIDE) WITH 3,4,5-TRIS(N-DODECAN-1-YLOXY)BENZOIC ACID AND OF THEIR POLYMETHACRYLATES INTO TUBULAR SUPRAMOLECULAR ARCHITECTURES DISPLAYING A COLUMNAR HEXAGONAL MESOPHASE

The synthesis of the monoesters of oligo(ethylene oxide) and octane-1, 8-diol with 3,4,5-tris(n-alkan-1-yloxy)benzoic acids and of their corr esponding polymethacrylates is described. The LiCF3SO3 complexes of th e monoesters of triethylene glycol with 3,4,5-tris(n-dodecan-1-yloxy)b enzoic acid (3-12-3), and with 3,4,5-tris(n-octadecan-1-yloxy)benzoic acid (3-18-3), as well as the polymethacrylates of the monoesters of m ono-(5-12-1), di-(5-12-2), tri-(5-12-3) and tetra-(5-12-4) ethylene gl ycol with 3,4,5-tris(n-dodecan-1-yloxy)benzoic acid self-assemble into a cylindrical supramolecular architecture which displays a columnar h exagonal (PHI(h)) mesophase. This cylindrical supramolecular architect ure was characterized by a combination of techniques including differe ntial scanning calorimetry, wide- and small-angle X-ray scattering, th ermal optical polarized microscopy, and molecular modelling. The chara cterization results suggest a model that resembles the cylindrical arc hitecture that forms by the self-assembly of low molar mass and polyme rized inverse micelles. A cross-section of the cylindrical assembly is constituted of about five molecules of 3-12-3 in its LiCF3SO3 complex or about four to five repeats units of 5-12-n with their oligooxyethy lenic segments melted and segregated in the inner core of the cylinder and their melted alkyl tails radiating towards the periphery of the c ylinder. The driving force for the cylindrical self-assembly is provid ed by a fine balance of exo- and endo-recognition processes. Exo-recog nition is the result of the tapered shape and hydrophobic character of the 3,4,5-tris(n-dodecan-1-yloxy)benzoate group. Endo-recognition is generated by either the combination of dipolar and ionic interactions of the oligo(ethylene oxide) receptor (LiCF3SO3 complex of 3-12-3) or the combination of dipolar interactions and covalent bonding (5-12-n). The necessity of the presence of endo-recognition for the self-assemb ly of the cylindrical supramolecular architecture is demonstrated by t he replacement of the oligo(ethylene oxide) receptor by a non-polar al iphatic spacer. Comparison between the 'molecular' polymethacrylate ba ckbone (in 5-12-3) and the 'supramolecular polymer backbone' (formed v ia ionic interactions in the complex of 3-12-3) indicates that in this particular example, the ionic interactions generated by the dissolved ion-pairs stabilize the supramolecular assembly to a greater extent t han does the covalent bonding.