James A. Heck

Poly{2-vinyloxyethyl 3,4,5-tris[4-(n-dodecanyloxy)benzyloxy]benzoate}: a self-assembled supramolecular polymer similar to tobacco mosaic virus

The synthesis of 2-vinyloxyethyl 3,4,5-tris[4-(n-dodecanyloxy)benzyloxy]benzoate (3), its cationic polymerization to poly{2-vinyloxyethyl 3,4,5-tris[4-(n-dodecanyloxy)benzyloxy]benzoate}(4) with relative number-average degrees of polymerization (DP) from 3.7 to 16 and narrow molecular-weight distributions (i.e. Mw/Mn⩽ 1.28), and the characterization of 4 by a combination of techniques consisting of differential scanning calorimetry, thermal optically polarized microscopy, and X-ray scattering experiments are presented. Regardless of molecular weight, compound 4 displays an enantiotropic columnar hexagonal (Φh) mesophase and an enantiotropic nematic (N) mesophase. The structural unit of 4 has a tapered shape. At low DP values (i.e. DP ⩽ 4) the tapered side-groups of 4 self-assemble into a disc-like supramolecular architecture which generates the Φh and the N mesophases. At DP ⩽ 4, 4 self-assembles directly into a column-like supramolecular architecture In this last case the backbone of the polymer penetrates through the middle of the column from which the tapered side groups are radiating out to the edge of the column. It is believed that the disc-like and column-like supramolecular architectures exist in the Φh, N, and the isotropic phases except that in the last one the structure lacks long-range positional order. The mechanism of self-assembly of 4 resembles that of the tobacco mosaic virus (TMV) except that in the first case the tapered side groups are linked to the polymer backbone via covalent bonds and in the latter case via non-covalent bonds.

Molecular recognition directed self-assembly of supramolecular cylindrical channel-like architectures from 6,7,9,10,12,13,15,16-octahydro-1,4,7,10,13-pentaoxabenzocyclopentadecen-2-ylmethyl 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate

Complexation of the crown ether receptor of the benzo-15-crown-5 benzoate 6[6,7,9,10,12,13,15,16octahydro-1,4,7,10,13-pentaoxabenzocyclopentadecen-2-ylmethyl 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate]6 with NaCF3SO3 and KCF3SO3 destabilizes the crystalline phase of 6 and induces the self-assembly of a supramolecular cylindrical channel-like architecture which displays an enantiotropic thermotropic disordered hexagonal columnar (Φh) mesophase. Characterization of this supramolecular architecture was performed by a combination of differential scanning calorimetry (DSC), X-ray scattering, thermal optical polarized microscopy, DC conductivity and molecular modelling. A model is proposed in which a stratum of the column is formed by ca. 5.8 molecules of 6 with their benzo-15-crown-5 receptors placed side-by-side in the centre of the column and their melted alkyl tails radiating towards its periphery. endo-Recognition generated via the benzo-15-crown-5 receptor upon complexation, and exo-recognition provided by the tapered 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate fragment of 6(most probably functioning via hydrophobichydrophobic interactions) provide the driving force for the self-assembly of this channel-like supramolecule. This mechanism of self-assembly resembles that of tobacco mosaic virus (TMV).

Re-entrant isotropic phase in a supramolecular disc-like oligomer of 4-[3,4,5-tris(n-dodecanyloxy)benzoyloxy]-4′-[(2-vinyloxy)ethoxy]biphenyl

The synthesis of 4-[3,4,5-tris(n-dodecanyioxy)benzoyloxy]-4′-[(2-vinyloxy)ethoxy]biphenyl (7), its cationic polymerization to poly{4-[3,4,5-tris(n-dodecanyloxy)benzoyloxy]-4′-[(2-vinyloxy)ethoxy]biphenyl}(8) with narrow molecular-weight distribution (Mw/Mn⩽ 1.25) and relative number-average degrees of polymerization (DP) from 2.7 to 8, and the characterization of the resulting oligomers by a combination of techniques consisting of differential scanning calorimetry, thermal optical polarized microscopy, and X-ray scattering experiments are presented. Compound 8 with DP = 3.2–3.9 displays a crystalline phase and a columnar hexagonal (Φh) mesophase at higher temperatures. Compound 8 with DP ≈ 5 exhibits a Φh mesophase and a thermodynamically stable enantiotropic re-entrant isotropic (Ire) phase. Compound 8 with DP > 5 is isotropic. The phase behaviour of the oligomers is explained based on the self-assembling of the tapered structural units of 8 into a supramolecular disc-like architecture in which the polymer backbone is confined to the centre of the disc-like supramolecule. The disc-like supramolecular architectures are responsible for the generation of Φh, Ire, and isotropic phases. Various structural suggestions for the influence of the molecular weight of 8 on its phase behaviour are discussed.

Molecular-Recognition-Directed Self-Assembly of Supramolecular Polymers

Abstract The first part of this paper discusses the molecular design of selected examples of structural units containing taper-shaped exo-receptors and various crown ether, oligooxyethylenic, and H-bonding-based endo-receptors, which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus. The ability of these structural units to self-assemble via a delicate combination of exo-and endo-recognition processes will be presented. A comparison between various supramolecular (generated via H-bonding, ionic, and electrostatic interactions) and molecular “polymer backbones” will be made. The present limitations concerning the ability to engineer the structural parameters of these supramolecular channel-like architectures and some possible novel material functions derived from them will be briefly mentioned. The second part of this paper discusses our research on the molecular design of a novel class of macrocyclics which self-assemble via intramolecular re...

Molecular Recognition Directed Self-Assembly of Supramolecular Architectures

This paper reviews some of our research on three classes of supra-molecular architectures which are generated via various combinations of molecular, macromolecular, and supramolecular chemistry. The ability of these supramolecular architectures to form liquid crystalline phases is determined by the shape of the self-assembled architecture and will be used to visualize it via various characterization techniques. The molecular design of selected examples of structural units containing taper-shaped exo-receptors and crown ether, oligooxyethylenic, and H-bonding based endo-receptors which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus (TMV), of macrocyclics which self-assemble into supramolecular rigid “rodlike” architectures and of hyperbranched polymers which self-assemble.into a willowlike architecture will be discussed. In the case of TMV-like supramolecular architectures, a comparison between various supramolecular(generated via H-bonding...

Molecular Recognition Directed Self-Assembly of Supramolecular Liquid Crystals

Abstract The first part of this paper discusses the molecular design of selected examples of structural units containing taper shaped exo-receptors and various crown ether, oligooxyethylenic, and H-bonding based endo-receptors, which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus (TMV). The ability of these structural units to self-assemble via a delicate combination of exo- and endo-recognition processes will be presented. A comparison between various supramolecular (generated via H-bonding, ionic, and electrostatic interactions) and molecular “polymer backbones” will be made. The formation of columnar hexagonal (Φh), nematic and re-entrant isotropic phases by selected self-assembled systems will be discussed. The present limitations concerning the ability to engineer the structural parameters of these supramolecular channel-like architectures and some possible novel material functions derived fiom them will be briefly mentioned. The seco...

Isomorphism within the hexagonal columnar mesophase of molecular and macromolecular self- and co-assembled columns containing tapered groups

Abstract The phase behaviour of binary mixtures of self-assembled tapering molecules based on monoesters of oligooxyethylene glycol and 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoic acid, their corresponding polymethacrylates, and of 4′-methyl (benzo-15-crown-5)-3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate within their hexagonal columnar mesophase (Φh) is described. The binary blends between molecular tapers co-assemble into a single supramolecular column resulting in isomorphism within their Φh mesophase over the entire range of composition. The binary blends between polymethacrylates containing tapered side groups co-assemble into a single Φh phase only when the columns of the parent polymers are of similar diameters. This results in binary mixtures which are isomorphic within the Φh mesophase over the entire composition range. When the diameters of the columns formed by the parent polymers are dissimilar, isomorphic mixtures are obtained only over a narrow range of composition. Binary mixture...

The influence of the complexation of sodium and lithium triflate on the self-assembly of tubular-supramolecular architectures displaying a columnar mesophase based on taper-shaped monoesters of oligoethylene oxide with 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzoic acid and of their polymethacrylates

The monoesters of mono-(1a), di-(1b), tri-(1c) and tetra-(ld) ethylene glycol with 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzole acid (1), the polymethacrylates derived from them (2) and the complexes of both 1 and 2 with LiCF3SO3 and NaCF3SO3 self-assemble into cylindrical supra-molecular architectures which exhibit a hexagonal columnar (Φh) mesophase. The generation of the Φh mesophase depends on the stabilization of this assembly by endo-recognition in the core of the cylinder (H-bonding and ionic interactions) and exo-recognition that occurs between the tapered groups and also between the cylinders (i.e., the hexagonal arrangement of the columns). The low molecular weight compounds 1 are able to complex more salt in the Φh mesophase and have larger increases in Φh–isotropic transition temperature (TΦh–i) per increase in salt concentration than the corresponding polymethylcrylates 2 derived from them. Molecular modelling appears to indicate that positional and conformational restrictions imposed by both the tapered side groups and the polymer backbone are responsible for these results. Both the polymers and the low molar mass compounds have their TΦh–i shifted to lower temperatures and allow more LiCF3SO3 to be complexed with the increase in the number of oxyethylene segments present in the flexible spacer. A comparison of the difference in the effectiveness of the Li cation versus the Na cation in providing increased stabilization of the Φh mesophase does not show any significant differences between the two cations.