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Synthesis and modes of self-assembly are described for the tapered monodendritic molecules 3,4,5-nGi-X of generation i = 1, 2, 3 (see structures below) that contain multiple (CH2)nH alkyl chains on their periphery (n = 12, 14, 16) and a polar group X at the apex (X = COOH, COONa, COOCs, CO(OCH2CH2)3OH). These monodendrons self-assemble into supramolecular cylindrical or spherical dendrimers, which in turn self-organise into p6mm columnar or Pm3n cubic thermotropic liquid crystals, respectively. The two principal ways of affecting the self-assembly of these compounds by means of their molecular architecture are: a) by changing the width of the wide (aliphatic) end, and b) by changing the volume at the apex. In the present work a) is controlled through temperature (conformational disorder) and b) is controlled by chaging the generation number i or the size of X, for example, through the choice of metal cation. The single most important geometric parameter of these dendritic building blocks is the molecular solid angle (taper angle) alpha; a high alpha leads to spherical and a low alpha to cylindrical supramolecular dendrimers. Furthermore, alpha also determines the equilibrium size of the supramolecular objects; a larger alpha results in a smaller diameter. The unusually strong negative thermal expansion coefficient of the cubic and columnar lattice is attributed to the excess of the increasingly highly tapered molecules being rejected from their parent aggregates and reassembling as new ones. Increasing alpha is also considered to be responsible for the observed thermotropic columnar-cubic transition.

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X-ray methods have been used to analyze the supramolecular tubular structures in the hexagonal solid state and columnar hexagonal liquid crystalline ( &, ) phases of a polymethacrylate with tapered side groups: specific~y,poly(2-(2-[2-(2-(methacryloyloxy)ethoxy)ethoxylethoxy)ethyl3,4,5-tris(@-(dodecyloxy)-benzyl)oxy)benzoate), abbreviated as 12-ABG-4EO-PMA. Oriented fibers were drawn from the liquid crystalline phase at -60 O C and annealed for several days at 4 "C. The X-ray pattern for these fibers recorded at room temperature (25 "C) contained eight equatorial reflections that are orders predicted for a hexagonal unit cell with a = b = 60.4 A. The similarity of the data to those for unoriented specimens in the & phase suggests that both phases contain the same type of supramolecular cylindrical moieties. In addition, wideangle maxima are observed on the equator and two layer lines that suggest formation of a three-dimensionallyordered structure at room temperature. These data give the first available information on the supramolecular structure within the columns. The layer line spacings define a repeat of c = 5.03 A along the column axis, containing eight monomeric units based on the observed density. Strong off-meridional maxima at d = 4.30 and 3.84 A on the first layer line suggest that the "planes" of the aromatic moieties are tilted rather than perpendicular to the cylinder axis. Possible "pine tree" models are discussed in which the tapered side groups are stacked in 8-fold layers or form &fold helices within the columns. Increasing the temperature to 60 O C leads to a reduction in the cylinder diameter to 58.0 A. Stacking correlations remain along the fiber axis direction, but otherwise the internal structure of the cylinder is muchmore disordered than at room temperature. On cooling, the three-dimensional order is restored.

The synthesis of the monoesters of oligo(ethy1ene oxide) and octane-I ,8-diol with 3,4.5-tris(nalkan-1 -yloxy) benzoic acids and of their corresponding polymethacrylates is described. The LiCF,SO, complexes of the monoesters of triethylene glycol with 3,4,5-tris(n-dodecan-l -yloxy)benzoic acid (3-1 2-3). and with 3.4.5-tris(n-octadecan-I -yloxy) benzoic acid (3-1 8-3), as well as thepolymethacrylatesofthemonoestersof mono-(5-1 2-1 ),di-(5-12-2),tri-'(5-12-3) andtetra-(5-1 2-4) ethylene glycol with 3,4,5-tris(n-dodecan-l -yloxy) benzoic acid self-assemble into a cylindrical supramolecular architecture which displays a columnar hexagonal (Oh) mesophase. This cylindrical supramolecular architecture was characterized by a combination of techniques including differential scanning calorimetry, wide-and small-angle X-ray scattering, thermal optical polarized microscopy, and molecular modelling. The characterization results suggest a model that resembles the cylindrical architecture that forms by the self-assembly of low molar mass and polymerized inverse micelles. A cross-section of the cylindrical assembly is constituted of about five molecules of 3-12-3 in its LiCF,SO, complex or about four to five repeats units of 5-12-17 with their oligooxyethylenic segments melted and segregated in the inner core of the cylinder and their melted alkyl tails radiating towards the periphery of the cylinder. The driving force for the cylindrical self-assembly is provided by a fine balance of exo-and endo-recognition processes. Exo-recognition is the result of the tapered shape and hydrophobic character of the 3,4,5-tris(n-dodecan-I -yloxy) benzoate group. Endorecognition is generated by either the combination of dipolar and ionic interactions of the oligo(ethy1ene oxide) receptor (LiCF,SO, complex of 3 -1 2-3) or the combination of dipolar interactions and covalent bonding (5-1 2-17). The necessity of the presence of endo-recognition for the self-assembly of the cylindrical supramolecular architecture is demonstrated by the replacement of the oligo(ethy1ene oxide) receptor by a non-polar aliphatic spacer. Comparison between the 'molecular' polymethacrylate backbone (in 5-1 2-3) and the 'supramolecular polymer backbone' (formed via 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 than does the covalent bonding.