Structural and transport phenomena of urocanate-based proton carrier in sulfonated poly(ether ether ketone) membrane composite

Proton transport is one of crucial phenomena in electrolytic part highly considered to overcome a limit in fuel cell efficiency improvement. Proton conducting organic electrolyte was modeled and simulated at atomistic level of calculation by doping of butyl urocanate (C4U), a composite material with imidazole substructure, with sulfonated poly(ether ether ketone) (SPEEK) amorphous membrane at various working temperature. Molecular dynamics simulations were used to investigate structural and dynamics characteristic of C4U in the membrane comparing with the SPEEK-hydronium membrane model as a control. From simulations, thermal effect on water and proton carriers cluster surrounding the sulfonate groups was explored. At higher temperature, the more transport dynamics of C4U ions in SPEEK membranes were found than that of hydronium ions in the control system. Likewise, phase separation of hydrophobic and hydrophilic parts was taken into consideration here. A critical role of the enhancing proton conductivity by increasing the diffusion coefficient at temperature beyond C4U melting point in composite polymer membrane was emphasized. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1625–1635     

Structural Study of Phase Transition Behavior of Uniaxially-Oriented Ethylene-Tetrafluoroethylene Alternating Copolymer

Crystal modifications and phase transition behavior have been investigated for the uniaxially-oriented ethylene-tetrafluoroethylene alternating copolymer samples of equimolar content by the temperature-dependent X-ray diffraction and Raman spectral measurements. The X-ray fiber diagram measured for the sample drawn at 0 °C has been found to be quite different from that drawn above 100 °C or the normal orthorhombic-type sample. The new X-ray diagram is characterized by the sharpness of the reflections and the positional shift from the horizontal lines, indicating the tilting phenomenon of the crystallites. This sample was found to transform into the hexagonal phase in the temperature region around 110 °C with keeping the tilting phenomenon. The molecular motion of the more or less conformationally disordered chains was enhanced above this transition region as seen from the increase in the half-width of trans bands and the intensity increment of gauche bands in the Raman spectra.     

Inclusion Compounds Formed from N,N-bis(2-hydroxybenzyl)alkylamine Derivatives and Transition Metal Ions via Molecular Assembly

A series of N,N-bis(2-hydroxybenzyl)alkylamine derivatives (1–5) have been found to form host–guest compounds with transition metal ions. The inclusion phenomena in solution are confirmed from the new peak at 415?nm observed by UV-Vis (ultraviolet-visible) spectroscopy and the aromatic and methylene peak shifts observed by ¹H NMR (proton nuclear magnetic resonance) spectroscopy. Comparative studies on 1–5 by liquid–liquid extraction studies suggest that the bulky group at the aza position of the derivatives obstructs the ion interaction resulting in the decrease in ion extraction ability. Inclusion depends on the interaction of the transition metal ions with the compounds 1–5 at the aza and hydroxyl groups as identified by the two-dimensional nuclear Overhauser enhancement technique (¹H–¹H NOESY). The results from Job's plot and electrospray ionization mass spectroscopy (ESIMS) imply molecular assembly of the host–guest system in a 2:1 ratio. Comparative studies among different ions, i.e., Cu²⁺, Zn²⁺ and Cd²⁺ suggest that the host–guest formation is effective when electron sharing is possible through the outer orbital of the transition metal ions. In the case of inclusion in the solid state, the FTIR (Fourier transform infrared) spectra show the changes in vibrational mode of the functional groups in host molecules whereas the X-ray diffraction (XRD) patterns suggest a change in the packing structure of the host molecules. After host–guest formation, the thermal stability of the host molecules decreases as a result of the change in the packing structure from a hydrogen-bonded network to one of ionic interaction with the guest.     

Synergistic effects of a specific metal template and H-bonds in controlling macrocyclization: a simple, selective, and effective cyclization from N,N-bis(2-hydroxybenzyl)alkylamine derivatives

A macrocyclic compound obtained from a simple, selective, and effective reaction between N,N-bis(2-hydroxybenzyl)alkylamine derivatives and 1,3-bis(tosyloxy)propane is a good example of a cyclization controlled by synergistic effects of a metal template and hydrogen bonds.     

Selective crown ether based macrocyclization: a model case study from N,N-bis(2-hydroxyalkylbenzyl)alkylamine

A model case of selective crown ether based macrocycles, i.e., [1+1] or [2+2] macrocycles, obtained from a simple reaction of N,N-bis(2-hydroxyalkylbenzyl)alkylamine, HBA, and ditosylated compounds is proposed. For HBA with the methyl group at ortho and para positions, and at N atom, 1, the reaction between this derivative and the ditosylated compound with three, four, five, or eight atom chain length gives only a [1+1] macrocycle. For HBA with the methyl group at ortho and para positions, but a cyclohexyl group at N atom, 2, the reaction gives both [1+1] and [2+2] macrocyclic types when reacting with the ditosylated compound. The present work indicates that the structure of HBA induces selective macrocyclization to provide both [1+1] and [2+2] macrocycles.     

Supramolecular structure of N,N-Bis(2-hydroxybenzyl)alkylamine: flexible molecular assembly framework for host without guest and host with guest

N,N-Bis(2-hydroxybenzyl)alkylamine derivatives form a cage-like assembly consisting of two molecules via inter- and intramolecular hydrogen bonds. The derivatives exhibit themselves as host to accept copper-ion guests under the double-oxygen-bridged dimeric system. Quantum chemical calculation suggested that the host-guest interaction is based on a charge-transfer coordination. Comparison of the crystal structures before and after complexation clarifies a rare example of a host-guest compound where the hosts maintain their cage framework through the change of hydrogen bonds to coordination bonds.     

Supramolecular Structure of N,N-Bis(2-hydroxy-benzyl)alkylamine: From Hydrogen Bond Assembly to Coordination Network in Guest Acceptance

N,N-Bis(2-hydroxybenzyl)alkylamine ( HBA ) was described as a model to simplify the supramolecular system of polybenzoxazines. The single crystal X-ray analysis revealed that HBA forms a dimeric assembly based on its simultaneous inter- and intramolecular hydrogen bond network. When the HBA accepted the copper ion, the dimeric assembly HBA changed its primary hydrogen bond network to charge transfer coordination as clarified by the single crystal analysis as well as the superimposed structure based on DMol³ calculation. The supramolecular structure of HBA and copper also exhibited the role of solvent molecules in the packing structure which is a rare example showing the host accepts not only the metal ions but also the neutral molecules in the same time. The cyclization of HBA with esters or ethers to macrocyclic compounds was also an important model reaction to show how the backbone molecules self-stabilized with the hydrogen bond network initiate the simple, effective and efficient macrocyclic reaction.