Ionic liquid crystals derived from the protonation of poly(propylene imine) dendrimers with a cholesterol-based carboxylic acid

The liquid crystalline character of salts resulting from the interaction of poly(propylene imine) dendrimers with 3-cholesteryloxycarbonylpropanoic acid has been studied. The supramolecular structure and consequently the observed liquid crystalline phases are dictated by the degree of protonation of primary amino groups as compared with that of tertiary ones, determined by FTIR spectroscopy in the bulk and by NMR spectroscopy in solution. Glass transition temperatures of the materials are about 38°C. At higher temperatures they are transformed to smectic C* phases while a second-order smectic C phase to smectic A phase transition is observed between 90 and 110°C depending on dendrimer generation. At about 150°C the onset of degradation is observed. The influence of the ionic dendrimeric scaffold on the thermotropic properties is discussed.     

Ionic liquid crystals derived from the protonation of poly(propylene imine) dendrimers with a cholesterol-based carboxylic acid

The liquid crystalline character of salts resulting from the interaction of poly(propylene imine) dendrimers with 3-cholesteryloxycarbonylpropanoic acid has been studied. The supramolecular structure and consequently the observed liquid crystalline phases are dictated by the degree of protonation of primary amino groups as compared with that of tertiary ones, determined by FTIR spectroscopy in the bulk and by NMR spectroscopy in solution. Glass transition temperatures of the materials are about 38°C. At higher temperatures they are transformed to smectic C* phases while a second-order smectic C phase to smectic A phase transition is observed between 90 and 110°C depending on dendrimer generation. At about 150°C the onset of degradation is observed. The influence of the ionic dendrimeric scaffold on the thermotropic properties is discussed.     

Hydrogen-bonded supramolecular poly(ether ketone)s

The preparation of 2,4-diamino-1,3,5-triazine telechelic poly(ether ketone)s (triazine PEKs) and the formation of supramolecular polymers with dodecyl-(α-ω)-bis(5-methyl-1,3-pyrimidine-2,4-dione) were investigated. Both structures interacted by complementing hydrogen-bonding units present at their respective chain ends, this being reminiscent of triple hydrogen bonding in DNA. The preparation of the triazine PEKs started from hydroxyl-terminated poly(ether ketone)s by a nucleophilic displacement reaction with 2,4-diamino-6-(4-fluorophenyl)-1,3,5-triazine. With this method and molecular weight control via the Carothers equation, a series of triazine PEKs with a complete degree of end-group functionalization were prepared. The structure of the polymers was proven by ¹³C NMR spectroscopy and matrix-assisted laser desorption/ionization spectroscopy. When mixed as a 1:1 complex in solution with dodecyl-(α-ω)-bis(5-methyl-1,3-pyrimidine-2,4-dione), short triazine PEKs (molecular weight = 5700 or 10,000) showed a temperature-dependent association behavior visible via dynamic NMR spectroscopy. Additional proof of the formation of a supramolecular, hydrogen-bonded network was derived from solid-state NMR spectroscopy, differential scanning calorimetry, and rheological investigations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 661–674, 2004     

Polystyrene latices containing dodecanamide‐modified poly(propyleneimine) dendrimers

Polymerization of styrene in aqueous dispersions of the dodecanamide derivative of poly(propyleneimine) dendrimer DAB‐dendr‐(NH₂)₆₄ and sodium dodecyl sulfate (SDS) produced stable latices. With initial SDS concentrations of 10 mM or less, molar ratios of SDS to dendrimer end groups ranging from 2.3:1 to 9.5:1, and less than 10 wt % of SDS relative to styrene, the polystyrene latices had diameters of 30–60 nm and coefficients of variation of diameters of less than 10% when measured by transmission electron microscopy. Higher concentrations of SDS gave more polydisperse latices. The polystyrene latices formed with SDS and the dodecanamide‐modified dendrimer were almost the same size and polydispersity as those formed with SDS and the parent primary amine dendrimer DAB‐dendr‐(NH₂)₆₄. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 597–605, 2003     

Hydrogen-bonded supramolecular complexes formed between isophthalic acid and pyridine-based derivatives

Two types of supramolecular liquid crystals were prepared through the formation of double hydrogen-bonded complexes between isophthalic acid (A) and two different groups of pyridine-based derivatives ( I n and I _a-e ). The first group of the base, I n (molecular formula 4-C_nH_2n+1OC₆H₄COOC₆H₄-N=N-C₅H₄N) homologues differ from each other by the number of carbon atoms (n) in the alkoxy chain, which varies between 8, 10, 12 and 14 carbons. The second group of the pyridine-based derivatives, I _a-e (molecular formula 4-X-C₆H₄COOC₆H₄-N=N-C₅H₄N) analogues differ from each other by the terminal polar substituent, X, that changes between OCH₃, CH₃, H, NO₂ and Br groups. In this manner two different groups of complexes are formed, one of them is A : 2I n, (Group A ), and the other is A : 2I _a-e , (Group B ). All complexes were investigated for their mesophase behaviour by differential scanning calorimetry and polarised light microscopy. The formation of 1:2 hydrogen-bonded complexes was confirmed by FTIR spectroscopy and binary phase diagrams. Most complexes A and B show nematic and/or SmA phases. X-ray diffraction of the SmA phase of a representative complex of type A indicates a layer distance corresponding to only half of the length of the H-bonded complexes which is interpreted by a phase structure where these complexes adopt a U-shape which intercalate and form non-polar SmA phases.     

Oligosaccharide-modified poly(propyleneimine) dendrimers: synthesis, structure determination, and Cu(II) complexation

The multiple application of reductive amination on primary amino groups of first and second generation poly(propyleneimine) dendrimers is used as a one-pot approach to introduce twice the amount of the oligosaccharide units as surface groups, compared to initially present amino groups in the first and second generation dendrimers. This was proven by (1)H NMR, MALDI-TOF-MS, and LILBID-MS analysis. The size of these dendrimers was determined by the hydrodynamic radius using pulsed field gradient NMR and dynamic light scattering. Molecular modeling confirmed the presence of dense-shell dendrimers. These dendrimers exhibit a generation dependent Cu(II)/dendrimer ratio in an aqueous environment, highlighting these materials as possible metal-carrier systems with a well-defined oligosaccharide protection shell for application in a biological environment.     

Mesomorphism of thermotropic poly(propyleneimine) dendrimers and phase equilibria in systems on their basis

The thermotropic mesomorphism of poly(propyleneimine) dendrimers of first, second, and third generations has been studied by the methods of polarization thermomicroscopy and DSC. Phase diagrams for the binary systems of dendrimers with n-amyloxy-n′-cyanobiphenyl calamite liquid crystal and hexa(pentyloxy)triphenylene discotic liquid crystal have been constructed. Measurements have been carried out over the entire concentration range at temperatures corresponding to the stable states of nematic, columnar, and isotropic phases. The effects of the chemical nature and shape of linear and cyclic mesogen molecules on the manifestation of mesomorphism in LC dendrimers are considered.     

Composition and plasticizing effect of poly(carboxylic acid) complexes with amino compounds

Poly(carboxylic acid)-dimethylalkylamine complexes were prepared and examined by various methods including infrared spectrometry and chemical titrations. FTIR measurements provided some of the most complete and detailed insights into the type and the stoichiometry of the acid-base complexes. A (1:1) stoichiometric complexation of the poly(carboxylic acid) with tertiary amines was involved in protic solvents. A threshold degree of complexation of 42% was obtained in such a macromolecular system. The equilibrium constant of the proton transfer reaction K was estimated to be independent on the alkyl chain length of the base reagent. Besides the formation of the acid-base complexes, a plasticizing effect of the amine derivatives was demonstrated by differential calorimetry. A T_g depression could be both attributed to the amine molecules linked to the polymer backbone via ionic bonds and to the free molecules dissolved within the free volume of the polymer.     

U-Shaped dimeric liquid crystals derived from phthalic acid

Details of the transitional properties of four homologous series of U-shaped liquid crystal materials, the benzene-1,2-di-(4-carboxyalkoxybenzylidene-4-n-alkylanilines), are presented. The spacers incorporate 3 to 6 methylene units, whilst terminal aliphatic chain lengths are varied from 1 to 12 units. Members of the two homologous series with an odd number of methylene units in the spacer form nematic and smectic phases as a function of terminal chain length. Materials with an even number of methylene units in the spacer are purely smectogenic, and in both series the first two homologues form only smectic B phases. For all four series the higher homologues show the phase sequence SF/I-SC-SA-I. X-ray diffraction studies have shown that these smectic phases are composed of molecules arranged in bilayers.     

Supramolecular ferroelectric liquid crystals. Hydrogen-bonded complexes between benzoic acids and chiral stilbazoles

Supramolecular ferroelectric liquid crystalline complexes have been obtained from 4-alkoxybenzoic acids and optically active trans-4-substituted-4'-stilbazoles. Chiral smectic C phases are induced by the formation of supramolecular mesogenic structure through the selective intermolecular hydrogen bond between the achiral benzoic acids and the chiral non-mesogenic stilbazoles.     

Synthesis and ferroelectric properties of chiral swallow-tailed liquid crystals derived from (L)-lactic acid

Three homologous series of chiral swallow-tailed materials derived from (L)-lactic acid were prepared. Structural effects on the mesomorphic and physical properties were investigated in terms of (i) the variation of non-chiral peripheral length chain, (ii) the variation of swallow-tailed groups and straight alkyl chain at the chiral tails, and (iii) lateral halogen substituents in the core of the molecules. The mesophases and their corresponding transition temperatures were identified by optical polarized microscopy and differential scanning calorimetry. The physical properties of the ferroelectric SmC * phases such as switching current, spontaneous polarization and electro-optical response were also measured and compared.     

Synthesis and ferroelectric properties of chiral swallow-tailed liquid crystals derived from (L)-lactic acid

Three homologous series of chiral swallow-tailed materials derived from (L)-lactic acid were prepared. Structural effects on the mesomorphic and physical properties were investigated in terms of (i) the variation of non-chiral peripheral length chain, (ii) the variation of swallow-tailed groups and straight alkyl chain at the chiral tails, and (iii) lateral halogen substituents in the core of the molecules. The mesophases and their corresponding transition temperatures were identified by optical polarized microscopy and differential scanning calorimetry. The physical properties of the ferroelectric SmC* phases such as switching current, spontaneous polarization and electro-optical response were also measured and compared.     

Hydrogen-bonded liquid crystals built from hydrogen-bonding donors and acceptors. Infrared study on the stability of the hydrogen bond between carboxylic acid and pyridyl moieties

Abstract

The stability of a hydrogen-bonded complex built through inter-molecular hydrogen bonding between carboxylic acid and pyridine fragments has been examined using infrared spectroscopy. Infrared spectra as a function of temperature have been recorded for the 1:1 complex of 4-hexyloxybenzoic acid and trans-4-propoxy-4′-stilbazole from the crystalline state to the isotropic state. A dependence of the stability of the hydrogen bond on molecular orientation is observed clearly in the infrared spectra. The spectra also suggest that the hydrogen bond is an unionized type with a double minimum potential energy.     

Hydrogen-bonded liquid crystals built from hydrogen-bonding donors and acceptors. Infrared study on the stability of the hydrogen bond between carboxylic acid and pyridyl moieties

The stability of a hydrogen-bonded complex built through inter-molecular hydrogen bonding between carboxylic acid and pyridine fragments has been examined using infrared spectroscopy. Infrared spectra as a function of temperature have been recorded for the 1:1 complex of 4-hexyloxybenzoic acid and trans-4-propoxy-4'-stilbazole from the crystalline state to the isotropic state. A dependence of the stability of the hydrogen bond on molecular orientation is observed clearly in the infrared spectra. The spectra also suggest that the hydrogen bond is an unionized type with a double minimum potential energy.     

Interpolymer complex between poly(ethylene oxide) and poly(carboxylic acid)

An interpolymer complex was prepared by mixing aqueous solutions of poly(ethylene oxide) (PEO) and of a poly(carboxylic acid), i.e., poly(acrylic acid)(PAA), poly(methacrylic acid)(PMAA), or styrene-maleic acid copolymer(PSMA). The complexation mechanism was discussed on the basis of results of such experimental methods as viscosity, potentiometric titration, and turbidimetry. The hydrogen bond is primarily involved in these complexations, but the influence of hydrophobic interaction on complexation can not be ignored. If the degree of dissociation α of carboxylic acid or the degree of polymerization P_n of PEO was perceptibly changed, a stable complex was obtained at about α 0.1 or P_n (PEO) = 40 for PMAA, 200 for PAA. This fact indicates that more than a definite number of binding sites are necessary for a stable interpolymer complex to be formed and that cooperative interaction among active sites plays an important role in complex formation.     

Antiferroelectric liquid crystals derived from a new optically active (R)-3-ethylmercapto-2-methylpropionic acid

A new optically active (R)-3-ethylmercapto-2-methylpropionic acid has been synthesized using D(-)—2,10-camphorsultam as a chiral auxiliary. The optical purity of the acid obtained was greater than 98 per cent. Its derivatives, (R)-4-(3-ethylmercapto-2-methylpropionyl)phenyl 4'-alkoxybiphenyl-4-carboxylates (EMMPPmBC; m = 7-16), have been prepared for the investigation of liquid crystalline properties as a function of peripheral alkyl chain length. Optical studies showed that all members exhibited an antiferroelectric S*c_A phase. The results also indicate that a lengthened alkyl chain length is favoured for S_cA* phase formation.     

Formation and manipulation of supramolecular structures of oligo(p-phenylenevinylene) terminated poly(propylene imine) dendrimers

A third generation poly(propylene imine) dendrimer modified with pi-conjugated oligo(p-phenylenevinylene)s forms spherical and rod-like aggregates that can be manipulated by optical tweezers.