Dimitris Tomazos

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...

The influence of the polymer backbone flexibility on the phase transitions of side chain liquid crystal polymers containing 6-[4-(4-methoxy-β-methylstyryl)phenoxy]hexyl side groups

SummaryThe influence of the polymer backbone flexibility on the phase transition temperatures of side chain liquid crystalline polymethacrylate, polyacrylate, polymethylsiloxane, and polyphosphazene containing 6-[4-(4-methoxy- β- methylstyryl)phenoxy]hexyl side groups is discussed. Flexible backbones enhance the decoupling of the motions of the side chain and main chain and therefore, increase the rate of side-chain crystallization. Subsequently, the kinetically controlled crystallization process may transform the thermodynamically controlled mesomorphic phases from enantiotropic into monotropic. However, the highest degree of order in the mesophase is exhibited by the polymers based on the most rigid polymer backbone.

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...

Can the rigidity of a side-chain liquid-crystalline polymer backbone influence the mechanism of distortion of its random-coil conformation?

Abstract The relationship between the isotropization transition temperatures and the associated entropy changes of two series of side-chain liquid-crystalline polymers based on three different polymer backbones (polymethacrylate, polyacrylate and polymethylsiloxane) and 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene mesogenic side-groups attached to the polymer backbone through different flexible spacers is discussed. In the case of polymers containing long flexible spacers, isotropization transition temperatures, which are mostly dictated by the side-groups, are higher for polymers based on flexible backbones, suggesting that they provide the highest degree of order in the mesophase. Therefore, their mesophase should exhibit the lowest entropy and the highest entropy change of isotropization. However, experimentally determined entropy changes of isotropization, which refer to the overall degree of order of the polymer, present the highest values for polymers based on the most rigid backbone. Two different mechanisms of distortion of the random-coil conformation of flexible and rigid polymer backbones are suggested to account for this contradictory result. A squeezed random-coil conformation, which in the case of smectic polymers is confined between the smectic layers, is considered for flexible backbones. An extended-chain conformation is considered for rigid backbones. The entropy associated with the squeezed random-coil conformation is higher than that associated with the extended conformation, and therefore the overall order that results from the combination of backbone and the organization of the mesogenic side-groups may explain the experimentally observed isotropization entropy changes. Polymers based on short flexible spacers exhibit similar entropy changes of isotropization irrespective of the nature of their backbone. This may suggest an extended backbone conformation for polymers based on short spacers and rigid or flexible backbones.

Liquid crystalline copoly(vinylether)s containing 4(4′)-methoxy-4′ (4)-hydroxy-α-methylstilbene constitutional isomers as side groups

SummaryEthoxy vinyl ethers containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers as side groups were synthesized by phase transfer catalyzed etherification of a Mixture containing the above mentioned isomers with 2-chloroethyl vinyl ether. Cationic copolymerization of various ratios between the two constitutional isomeric monomers led to a mixture of two copolymers which were separated by fractional precipitation. One copolymer exhibits a nematic mesophase, the other exhibits two smectic mesophases.

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...

Mesomorphic polyelectrolytes based on side-chain liquid-crystalline polymers containing side-on fixed mesogens and oligooxyethylenic spacers

The synthesis and characterization of side-chain liquid-crystalline polysiloxanes based on 4′-cyanobiphenyl-4-yl 4-{2-[2-(2-allyloxyethoxy)ethoxy]ethoxy}benzoate (11a-3), 4′-cyanobiphenyl-4-yl 4-[2-(2-allyloxyethoxy)ethoxy]benzoate (11a-2), 4′-methoxybiphenyl-4yl 4-{2-[2-(2-allyloxyethoxy)ethoxy]ethoxy}benzoate (11b-3) and 4′methoxybiphenyl-4-yl 4-[2-(2-allyloxyethoxy)ethoxy]benzoate (11b-2) and of copolysiloxanes containing structural units derived from monomer 11a-2 and 2-(2-allyloxyethoxy)ethyl methyl ether (3-2), and from monomer 11a-3 and 2-[2-(2-allyloxyethoxy)ethoxy]ethyl methyl ether (3-3), are presented. The polysiloxanes based on 11a-3 and 11a-2 display an SA mesophase, while the polysiloxanes based on 11b-3 and 11b-2 display N, and SA and N mesomorphism, respectively. All copolysiloxanes display an SA mesophase. The complexation of the polysiloxane based on the monomer 11a-3(i.e.P-11a-3) with LiCF3SO3 led to an increase in their glass-transition temperatures and a decrease in their SA-I transition temperatures. These complexes are thermotropic liquid-crystalline polyelectrolytes which can accommodate up to 0.6 mol of salt per mole of ethylene oxide repeat unit (CH2CH2O).

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...

Semifluorinated polymers: 1. Synthesis and characterization of side chain liquid crystalline polymers containing semifluorinated oligooxyethylene based flexible spacers

Abstract The synthesis and characterization of polymethacrylates, polyacrylates and polysiloxanes containing 4-methoxy-4′-hydroxybiphenyl (4-BP), 4-methoxy-4′-hydroxy-α-methylstilbene (4-MS) and 4-hydroxy-4′-methoxy-α-methylstilbene (4′-MS) mesogenic groups and a semifluorinated triad based on tetrafluorooxetane, hexafluoropropylene oxide and trifluoroethylene oxide is described. All polymers display a SA mesophase and side chain crystallization. In the case of polymers based on 4-MS and 4′-MS the highest degree of decoupling seems to be displayed by the polymethacrylates. This result is in contrast to the behaviour of the corresponding polymers containing aliphatic spacers. The polymethacrylate based on 4-BP displays an unusual ‘inverse’ monotropic SA·mesophase which to our knowledge was not previously encountered in any liquid crystal systems. The synthesis and characterization of copolymethacrylates and copolysiloxanes containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers is also described.

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.