Number Of Methylene Units Research Articles

Fabrication of Nanotubules and Microspheres from the Self-Assembly of Amphiphilic Monochain Stearic Acid Derivatives

A series of amphiphilic monochain derivatives of stearic acid, CH(3)(CH(2))(16)CONH(CH(2))(n)NH(2) (n = 2, 3, 4, 6), CH(3)(CH(2))(16)CONH(CH(2))(2)S(2)(CH(2))(2)NH(2), and [CH(3)(CH(2))(16)CONH](2)(CH(2))(2), are synthesized, and their self-assembly behaviors have been investigated in 1,2-dichloroethane (DCE). In addition to the concentration of the compound in DCE, the number of methylene units in hydrophilic segments play a crucial role in determining the final morphology of self-assembling structures from nanotubules with 20 nm inner diameter to microspheres with an average diameter of 20 μm. The external texture of the microsphere is also influenced by the number of methylene units in the hydrophilic segment. The microspheres formed by highly ordered aggregation of nanobelts show high thermal stability. The particular processes and causations have been expatiated.

Dimer acid-based thermoplastic bio-polyamides: Reaction kinetics, properties and structure

New dimer acid-based-polyamides were synthesized with rapeseed oil-based dimer acid (DA) and 1,2-diaminoethane, 1,6-diaminohexane or 1,8-diaminooctane to form DAPAe, DAPAh and DAPAo, respectively. Effects of diamine chain lengths on kinetics evolution as well as on the thermal, physical and mechanical properties of the different polyamides synthesized were investigated. DAPAo was found to be the most reactive diamine because of its higher nucleophilic character. Differential scanning calorimetry (DSC) combined with X-ray diffraction revealed a low-order semi-crystalline structure for all polyamides. A tentative schema for the structural organization of these DAPA is proposed and shows a specific organization with local semi-crystalline segregation domains. DAPAe was found to possess the higher melting temperature likely due to higher crystal cohesion, which was confirmed by higher Young modulus in stress-strain experiments. Rheological data showed an increase of the glass transition temperature concomitantly with the increase of diamine chain length. They also revealed an increase of complex viscosity with the diamine chain length. Investigation of thermal stability showed that DAPAe degrades before DAPAh and DAPAo in connection with the number of methylene units per diamine.

Supramolecular Liquid Crystalline π-Conjugates: The Role of Aromatic π-Stacking and van der Waals Forces on the Molecular Self-Assembly of Oligophenylenevinylenes

Here, we report a unique design strategy to trace the role of aromatic π-stacking and van der Waals interactions on the molecular self-organization of π-conjugated building blocks in a single system. A new series of bulky oligophenylenevinylenes (OPVs) bearing a tricyclodecanemethylene (TCD) unit in the aromatic π-core with flexible long methylene chains (n = 0-12 and 16) in the longitudinal position were designed and synthesized. The OPVs were found to be liquid crystalline, and their enthalpies of phase transitions (also entropies) showed odd-even oscillation with respect to the number of carbon atoms in alkyl chains. OPVs with an even number of methylene units in the side chains showed higher enthalpies with respect to their highly packed solid structures compared to odd-numbered ones. Polarized light microscopic analysis confirmed the formation of cholesteric liquid crystalline (LC) phases of fan shaped textures with focal conics in OPVs with 5 ≤ n ≤ 9. OPVs with longer alkyl chains (OPV-10 to OPV-12) produced a birefringence pattern consisting of dark and bright ring-banded suprastructures. The melting temperature followed a sigmoidal trend, indicating the transformation of molecular self-organization in OPVs from solid to ring-banded suprastructures via cholesteric LC intermediates. At longer alkyl chain lengths, the van der Waals interactions among the alkyl chains became predominant and translated the mesogenic effect across the lamellae; as a consequence, the lamellae underwent twisted self-organization along the radial growth direction of the spherulites to produce bright and dark bands. Scanning electron microscope (SEM) analysis of cholesteric LC and ring-banded textures strongly supported the existence of twisted lamellae in the OPVs with ring-banded textures. Variable temperature X-ray diffraction analysis confirmed the reversibility of the molecular self-organization in the solid state and also showed the existence of the higher ordered lamellar structure in ring-banded OPVs. Photophysical characterizations such as excitation, emission, and time resolved fluorescence decay measurements were employed to trace molecular self-organization in their liquid crystalline phases. The emission spectra of the OPV samples showed odd-even oscillation in their emission wavelengths with respect to the length of alkyl chains. Highly packed even-OPVs showed more blue shift compared to that of less crystalline odd-OPVs. Time dependent fluorescence decay of OPVs followed a biexponential fit, and their lifetimes (τ(1) and τ(2) values) revealed that the decay is faster for odd-OPVs compared to even-OPVs. Among all the OPVs, the τ(2) values for OPV-8 and OPV-12 were found to be much higher, indicating their high luminescent characteristics. In a nut shell, bulky liquid crystalline OPV chromophores were cleverly utilized, for the first time, to probe the aromatic π-stacking versus van der Waals interactions on the molecular self-organization of π-conjugated system.

Tuning Down of Color Transition Temperature of Thermochromically Reversible Bisdiynamide Polydiacetylenes

A series of bisdiynamide lipids containing various lengths of methylene spacer (m = 2, 3 and 4) between the diynes and the diamide headgroup and number of methylene units (n = 6 and 9) in their hydrophobic tails are synthesized. All six lipids synthesized can be dispersed in water and photopolymerized by UV irradiation to give the corresponding polydiacetylene (PDA) sols. The color transitions from blue to red during heating−cooling cycles of the PDA sols are photographically recorded and monitored by UV−vis absorption spectroscopy. The bisdiynamide PDAs exhibit excellent thermochromic reversibility and the color transition temperature can be tuned between ca. 25−55 °C by the variation of m and n values. Temperature indicators can be obtained by applying a screen printing ink formulated from the bisdiynamide monomer on plastic substrates followed by UV irradiation to generate desired patterns of thermochromically reversible PDAs.

ChemInform Abstract: 4-Dihydroxyborylphenyl Analogues of 1-Aminocyclobutanecarboxylic Acids: Potential Boron Neutron Capture Therapy Agents.

A series of 4-dihydroxyborylphenyl analogues of an unnatural α-amino acid, 1-aminocyclobutanecarboxylic acid (ACBC), was synthesized. Varying numbers of methylene units were introduced between the 4-boronophenyl and ACBC moieties in order to introduce different degrees of lipophilicity into the molecules. The key step in the syntheses was the preparation of the precursor p-boronophenyl-substituted cyclobutanones which were subsequently converted to the desired amino acids via the Bucherer−Strecker reaction.

Synthesis and characterization of polyepichlorohydrin-based copolymers with biphenyl groups attached thioether unit

Three novel copolymers, poly[1-(4-(benzothiazole-2-thio-alkyloxy)-biphenyl-4′-oxy)2.3-epoxypropane]s, were synthesized by the reaction of polyepichlorohydrin with obtained monomers, 4-(benzothiazole-2-thio-alkyloxy)biphenyl-4′-ols, in which the number of methylene unit in substitution group of biphenyl group was 2, 4, 6, respectively. The structures of obtained compounds were confirmed by elemental analysis and 1H NMR. The decomposition temperatures of copolymers were near 340 °C. Differential scanning calorimetry (DSC) measurement and polarized optical microscopy (POM) observation showed the resulting copolymers did not exhibit thermotropic liquid crystalline mesomophism and belonged to semi-crystalline substance.

Self-Assembly, Dynamics, and Phase Transformation Kinetics of Donor−Acceptor Substituted Perylene Derivatives

The role of alkyl chain substitution on the phase formation and core dynamics is studied in a series of diphenylamine functionalized perylenemonoimides (PMIs), by X-ray scattering, calorimetry and site-specific solid-state NMR techniques. In addition, the strong dipole associated with the donor-acceptor character of the molecules allow an investigation of the dynamics with dielectric spectroscopy. The self-assembly revealed an ordered phase only in PMIs with branched alkyl chains. This phase comprises a helical stacking of molecules with a molecular twist angle of 60 degrees. Results from solid-state NMR further pointed out the importance of intramolecular hydrogen bonding in stabilizing the intracolumnar packing within the ordered phase. Moreover, the core dynamics are frozen as revealed by the value of the dynamic order parameters and the reduced strength of dipolar relaxation. The kinetics of phase transformation from the isotropic to the ordered phase proceeds via a nucleation and growth mechanism, and the rates are dominated by the nucleation barrier. Within the isotropic phase the core dynamics display strong temperature dependence with rates that depend on the number of methylene units in the alkyl chains.

Curing behavior of epoxy resins with a series of novel curing agents containing 4,4′-biphenyl and varying methylene units

Abstract A new homologous series of curing agents (LCECAn) containing 4,4′-biphenyl and n-methylene units (n = 2, 4, 6) were successfully synthesized. The curing behaviors of a commercial diglycidyl ether of bisphenol-A epoxy (E-51) and 4,4′-bis(2,3-epoxypropoxy)biphenyl (LCE) by using LCECAn as the curing agent have been investigated by differential scanning calorimetry (DSC), respectively. The Ozawa equation was applied to the curing kinetics based upon the dynamic DSC data, and the isothermal DSC data were fitted using an autocatalytic curing model. The glass transition temperatures (Tg) of the cured epoxy systems were determined by DSC upon the second heating, and the thermal decomposition temperatures (Td) were obtained by thermogravimetric (TG) analyses. The results show that the number of methylene units in LCECAn has little influence on the curing temperatures of E-51/LCECAn and LCE/LCECAn systems. In addition, the activation energies obtained by the dynamic method proved to be larger than those b...

트리-0-[4-{4`-(시아노페닐아조)페녹시}]알킬 셀룰로오스들의 열방성 액정 거동

초록 · 키워드 목차 오류제보하기 등록된 정보가 없습니다. #Cellulose #cyanoazobenzene #nematic phase #spacer Length 등록된 정보가 없습니다.

Helical Crystal Assemblies in Nonracemic Chiral Liquid Crystalline Polymers: Where Chemistry and Physics Meet

Chirality transfer (or amplification) in soft materials is an important topic for understanding how chiral assemblies develop from the atomic level to macroscopic objects. This is an interdisciplinary area which is critically associated with the evolution from asymmetric chemistry to asymmetric physics, and, more specifically, in biomaterials, liquid crystals, and polymers. In this review, we discuss our recent studies on the conditions for chirality transfer across different length scales. We observed that the formation of helical structures in different length scales is a typical process in chirality transfer. This is illustrated by a series of nonracemic chiral main-chain liquid crystalline (LC) polyesters, PETs(R*-n). The polymers contained a different number of methylene units in the chain backbone (from 7 to 11). All of the PETs(R*-n) macroscopically exhibited an LC chiral smectic C (SC*) phase, a chiral smectic A (SA*) phase, and a twist grain boundary smectic A (TGBA*) phase with increasing temperature. The atomic chiral centers caused the helical conformation, and then, helical lamellar crystals were found in these polymers. The crystal structures were determined by X-ray diffraction and electron diffraction techniques. Dark field transmission electron microscopic images revealed that the molecular orientation in these helical crystals is double twisted. Our systematic studies showed that chirality transfer from one length scale to another is neither automatic, nor necessary, and it critically depends upon the packing scheme of the chiral building blocks on each length scale. It was particularly surprising that in this series of polyesters, the odd−even effect exists across many length scales. This includes not only thermodynamic properties such as the SC*, the SA*, and the TGBA* LC phase transition temperatures, but also the helical crystal handedness.

Synthesis and thermal properties of polythioether‐based liquid‐crystalline polymers containing azobenzene in the side chain

AbstractBACKGROUND: Owing to the unusual structural rearrangement of polychloromethylthiirane (PCMT) at room temperature, it has not been used as the main‐chain backbone of side‐chain liquid‐crystalline polymers (SLCPs). However, it has been observed that PCMT has a relatively stable and clear structure under special conditions. Therefore, we attempted to synthesize SLCPs using PCMT as main‐chain backbone and investigated their thermal behavior.RESULTS: New polymers, poly[1‐({(4‐methoxyazobenzene‐4′‐oxy)alkyl}thio)‐2,3‐epithiopropane], in which the number of methylene units in the alkyl group is 4, 5 or 6, were prepared by means of reactions of corresponding (4‐methoxyazobenzene‐4′‐oxy)alkylthiols with PCMT. The structures of these compounds were confirmed using elemental analysis and 1H NMR spectroscopy. The substitution ratios of the copolymers with 4, 5 and 6 methylene units in the alkyl group were 56, 75 and 80%, respectively. Differential scanning calorimetry measurements and polarized optical microscopy observations showed that the resulting copolymers exhibited thermotropic liquid‐crystalline mesomorphism with nematic phase except for the copolymer with a 56% substitution ratio. The decomposition temperature of all the synthesized copolymers was near 195 °C.CONCLUSION: This investigation has demonstrated that PCMT polymerized for 8 h has the ability to act as a suitable main‐chain backbone for SLCPs. Moreover, SLCPs could be obtained only by the reaction of PCMT with thiolate salt containing mesogenic groups. The substitution ratios increased with increasing number of methylene groups in the spacer. Copyright © 2009 Society of Chemical Industry

Synthesis and thermal behaviours of side-chain liquid-crystalline poly[N-(4-methoxyazobenzene-4′-oxyalkyl)ethyleneimine

A series of side-chain liquid-crystalline polymers, poly[N-(4-methoxyazobenzene- 4′-oxyalkyl)ethyleneimine](PEnZO), has been synthesised in which the number of methylene units in spacers varies from two to six. The structures of the synthesised monomers and polymers were confirmed by infrared (IR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The thermal properties of these polymers have been investigated using differential scanning calorimetry (DSC), polarising optical macroscopic (POM) X-ray diffraction and thermogravimetric analysis (TGA). The test results indicated that the obtained polymers exhibited thermotropic liquid-crystalline mesomorphism of nematic type with schlieren textures. It was observed that the thermal behaviours of the polymers were strongly dependent on the degree of substitution and the length of spacers. Polymers containing less than 57% of mesogenic groups did not exhibit mesogenic phase and resembled amorphous polymer. A more pronounced odd–even effect in the melting points and their enthalpy changes was observed on increasing the spacer length in which the odd members displayed lower values, which were also slightly dependent on the substitution degree of polymers. The mesomorphic temperature ranges of odd members were wider than those of even members. The decomposition temperatures of copolymers were near 230°C.

Balancing Hydrogen Bonding and van der Waals Interactions in Cyclohexane-Based Bisamide and Bisurea Organogelators

The solvent dependence of the gelation properties, the thermotropic behavior, and the melting enthalpy of a series of enantiomerically pure cyclohexane-based bisamide and bisurea compounds are reported. The two series of gelators examined are related structurally with the intermolecular interactions responsible for gelation differing in a systematic manner through varying the length of the alkyl tail and the number of hydrogen bonding units present. The gelation properties of the compounds in decalin, DMSO, and 1-propanol were studied by FTIR spectroscopy and by comparison of the thermal stability of their gels as determined by dropping ball experiments and by differential scanning calorimetry (DSC). FTIR spectroscopy, supported by the single-crystal X-ray diffraction of a3, indicates that the gelator molecules are aggregated through intermolecular hydrogen bonding in all of the solvents examined. The thermal stability of the gels in apolar and polar solvents was found to be dependent primarily on the relative strength of intermolecular hydrogen bonding and van der Waals interactions, respectively, compared with the strength of solvent-gelator interactions. The results of DSC indicated that the contribution of the difference in intergelator van der Waals interactions, compared with the gelator-solvent van der Waals and hydrogen bonding interactions, provided by the alkyl tail to the stability of the gel has a linear relationship with the number of methylene units in alkyl chains of length greater than six. In polar solvents, this contribution lies between 3.5 and 4.2 kJ mol(-1) per methylene unit, and in apolar solvents, it is 2.2 kJ mol(-1). The hydrogen bonding interactions were weaker in polar solvents and hence gelation occurred only where sufficient compensation was provided by intergelator van der Waals interactions. The results show that the direct relation of gelation strength to changes in solvent properties is not possible and more complex relationships should be considered. Furthermore, it is apparent that the development of design rules for the construction of LMWG molecules incorporating more than one anisotropic growth element must take into consideration the role of the solvent in determining which of the contributions is dominant.

Temporal integration in nasal lateralization of homologous propionates

For nasal irritation from volatile chemicals, a version of Haber’s rule (k = CnT) can model the trade-off between concentration (C) and duration of exposure (T) to achieve a fixed sensory impact, e.g. threshold-level irritation or a fixed suprathreshold intensity. The term k is a constant. The exponent, n, represents how well the system integrates over time. An exponent of 1 indicates complete temporal integration: an x-fold increase in stimulus duration exactly compensates for cutting the concentration 1/x. An exponent greater than 1 indicates incomplete temporal integration: more than an x-fold increase in duration is needed. In a previous study of homologous alcohols, n varied systematically with number of methylene units: integration became more complete as the length of the carbon chain increased. To explore the generality of this finding, we tested homologous esters that differ in the number of methylene units: n-ethyl propionate, n-propyl propionate, and n-butyl propionate. Nasal lateralization was used to measure irritation thresholds. Human subjects received a fixed concentration of a single compound within each experimental session. Stimulus duration was varied to find the briefest stimulus that caused lateralizable irritation. Concentration and compound varied across sessions. Consistent with results with n-alcohols, integration became more complete as the number of methylene units increased. Lipid solubility varies with chain length; hence, solubility in the nasal mucosa may play a role in the dynamics of irritation. Further, preliminary analyses suggest that, for data pooled across both chemical series, n varies systematically with molecular parameters related to solubility and diffusion.

Structure–Activity Relationships of SSAO/VAP‐1 Arylalkylamine‐Based Substrates

Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) substrates show insulin-mimetic effects and are therefore potentially valuable molecules for the treatment of diabetes mellitus. Herein we review several structural and electronic aspects of SSAO arylalkylamine-based substrates. Two main modifications directly affect amine oxidase (AO) activity: 1) variation in ring substitution modulates the biological activity of the arylalkylamine ligand by converting a substrate into a substrate-like inhibitor, and 2) variation in the number of methylene units between the aromatic ring and the ammonium groups of the arylalkylamine substrates dramatically alters the oxidation rate between species. Furthermore, we review relevant information about mammalian SSAO/VAP-1 substrate selectivity and specificity over monoamine oxidases (MAOs).

Thermo-mechanical characteristics of UV-irradiated polyurethane elastomers extended with α, ω-alkane diols

A series of polyurethane elastomers were prepared by the reaction of poly ε-caprolactone and 4,4′-diphenylmethane diisocyanate. The prepolymer was extended using α, ω-alkane diols as chain extenders having 2–10 methylene units in their structure. The synthesized samples were irradiated for 50, 100 and 200 h in an ultra violet (UV) exposure unit. Modifications in the chemical structure before and after irradiation were characterized using Fourier Transform Infrared spectroscopy. The thermal and mechanical properties were affected by the ultra violet irradiation time and the number of methylene units in the chain extenders. The experimental results indicated that the morphological structure changed during irradiation as a consequence of hard segment and soft segment degradation.

Synthesis and study of new liquid crystalline compounds with an epoxy group

The influence of the transformation of a terminal double bond to an epoxide group in the series of compounds containing phenyl benzoate moiety as the mesogenic rigid core is investigated. The epoxide derivatives are obtained by biotransformation methods. The double bond or epoxide ring are separated by different numbers of methylene units from the phenyl ring of benzoic acid in its methoxy or decyloxyphenyl esters. The mesogenic properties of the synthesised compounds are investigated by optical microscopy, calorimetric and X‐ray methods. In contrast to methoxyphenyl esters most of decyloxyphenyl esters showed enantiotropic liquid crystalline behaviour. The replacement of the double carbon–carbon bond by the polar and bulky epoxy group destabilises the mesophase in almost all cases.

Banana‐shaped dopants for flexoelectric nematic mixtures

The synthesis is reported of new meta‐substituted quaterphenyls and several related dimers as dopants for nematic mixtures with flexoelectric properties. The number and nature of the terminal substituents is varied from apolar with a small dipole moment to polar with a strong dipole moment. The number of methylene units in the flexible aliphatic spacer between the polyfluorinated aromatic groups of the dimers is also varied. Dimers capable of banana‐shaped conformers induce an increase in the flexoelectric coefficients of mixtures containing them and reduce the clearing point to a small extent.

Synthesis and thermal properties of side‐chain liquid crystalline poly[1‐({(4‐methoxyazobenzene‐4′‐oxy)alkyl}thio)‐2.3‐epoxypropane

A novel series of side‐chain liquid crystalline copolymers, i.e. poly‐[1‐({(4‐methoxyazobenzene‐4′‐oxy)alkyl}thio)‐2.3‐epoxypropane]s, were synthesised in which the number of methylene units in the alkyl group of the side chain varies from 3 to 6. The structures of compounds obtained were characterised by elemental analysis and 1H NMR spectroscopy. Thermal properties were investigated using polarising optical microscopy, differential scanning calorimetry and X‐ray diffraction analysis. The synthesised thiols and corresponding polyepichlorohydrin‐based copolymers exhibited thermotropic liquid crystalline behaviour and nematic phases with schlieren textures. The thiols have lower transition temperatures than the corresponding copolymers. In addition, the degree of substitution of the copolymers synthesised increased with an increase in number of methylenes in the side chain. The phase transition temperatures increased and the mesomorphic temperature ranges widened with the increasing degree of substitution of the copolymers.

Charge-Transfer Patterns for [Ru(NH3)6]3+/2+ at SAM Modified Gold Electrodes: Impact of the Permeability of a Redox Probe

Electrochemical performance of a (Ru(NH3)6) 3+/2+ redox couple at gold electrodes modified by alkanethiol self assembled monolayer (SAM) films of the type (-SH -(CH2)n - CH3) with different number of methylene units (n = 2 to 10) in the presence and absence of glucose additives has been studied using fast scan cyclic and steady-state voltammetry. Specific scatter of measured rate constants caused by enhanced sensitivity of this probe to minor defects of SAMs has been observed in a general agreement with the published data for thicker SAMs (n = 9 to 18). In addition, we have disclo- sed the anomalous viscosity-imposed drop of the heterogeneous rate constant for the case of Au electrodes modified by thinner n-alkanethiol SAMs (n = 2, 4). Taking into the account the fact of (Ru(NH3)6) 3+/2+ couple's capability to penetrate into the SAM interior, we ascribe the obtained results to the manifestation of the solvent-friction mechanism under the condition where the redox species presumably together with a few of solvating water molecules reside in a SAM's peri- pheral interior marked by much higher local viscosity (slower dielectric relaxation) compared to the electrolyte solution.