Preparation of cellulosic soft and composite materials using ionic liquid media and ion gels

Cellulose - Ionic liquids (ILs) are powerful media for the modification and functionalization of cellulose. This review article discusses the preparation of cellulosic soft and composite materials...     

Stereochemistry-dependent, mechanoresponsive supramolecular host assemblies for fullerenes: a guest-induced enhancement of thixotropy

Self-assembly behaviors of a series of systems (G1, G2, and G3) possessing same organic building blocks based on a substituted anthracene have been investigated in decalin. G2 and G3 are dominated by head-to-tail (ht) and head-to-head (hh) type dimers of G1, respectively. G1 gives a thermoresponsive gel that behaves ideally, showing frequency-independent elastic and viscous moduli. Interestingly, G2 produces a thixotropic gel that shows the signature of structural relaxation, signifying the dynamic nature of the system. In contrast, G3 remains fluidlike. As investigated by scanning electron microscopy (SEM), in the assembly process of G2, first disklike nanoaggregates are formed, and in the second step these aggregates interact to construct the densely packed secondary assembly. A transition from secondary assembly to primary assembly under shear initiates the mechanoresponsive destruction of the gel. In the self-assembly process, G1 propagates in a one-dimensional fashion, whereas G2 and G3 can propagate in a two-dimensionional fashion. The same side orientation of the substituents in G3 facilitates the formation of a compact closed-shell-type structure, which results in the generation of isolated nanocrystals. The long-range weak interaction together with the capability of propagating in two dimensions is found to be essential for the construction of such a mechanoresponsive assembly. C(60) and C(70) could be incorporated successfully in G2 assembly to develop mechanoresponsive fullerene assemblies. The presence of fullerenes not only enhances the elastic properties of G2 but also intensifies the thixotropy. C(70) appears to be a superior guest in terms of property enhancement due to its better size fitting with the concave-shaped host.     

Synthesis of transparent block copolymers consisting of poly(diisopropyl fumarate) and poly(2-ethylhexyl acrylate) segments by reversible addition-fragmentation chain transfer polymerization using trithiocarbonates as the chain transfer agents

The reversible addition-fragmentation chain transfer polymerization of diisopropyl fumarate (DiPF) was carried out using ethyl 2-[[(dodecylthio)thioxymethyl]thio]-2-methylpropionate (T1) and 1,1′-(1,2-ethanediyl) bis[2-[[(dodecylthio)thioxymethyl]thio]-2-methylpropionate] (T2) as the monofunctional and difunctional chain transfer agents (CTAs) to synthesize poly(diisopropyl fumarate) (PDiPF) with a rigid chain conformation. The obtained PDiPF had a well-controlled molecular weight, molecular weight distribution, and structure of the chain ends. Size exclusion chromatography and NMR measurements revealed an excellent introduction efficiency (84–98%) of the terminal trithiocarbonate group into the polymer chain end. They were available as the monofunctional and difunctional macro-CTAs to synthesize the AB and ABA block copolymers, respectively. While the well-controlled block copolymers were solely obtained by the polymerization of 2-ethylhexyl acrylate as the second monomer in the presence of PDiPF as the macro-CTA, the block copolymerization of DiPF using poly(2-ethylhexyl acrylate) as the macro-CTA failed. The trithiocarbonate group at the chain end was completely removed by the reaction with n-butylamine and it was valid for the improvement of the coloration and other optical properties of the transparent polymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2584–2594     

Surface electronic structure of the (3 × 2) reconstruction induced by Yb on a Si(1 1 1) surface

We have investigated the electronic structure of the Yb/Si(1 1 1)-(3 × 2) surface using angle-resolved photoelectron spectroscopy. Five surface states have been identified in the gap of the bulk band projection. Among these five surface state, the dispersions of three of them agree well with those of the surface states of monovalent atom adsorbed Si(1 1 1)-(3 × 1) surfaces. The dispersions of the two other surface states agree well with those observed on the Ca/Si(1 1 1)-(3 × 2) surface, whose basic structure is the same as that of monovalent atom adsorbed Si(1 1 1)-(3 × 1) surfaces. Taking these results into account, we conclude that the five surface states observed in the band gap originate from the orbitals of Si atoms that form a honeycomb-chain-channel structure.     

Precise determination of rare earth elements in rocks by neutron activation analysis

A pre-irradiation group separation method has been developed for the neutron activation analysis of rare earth elements (REE) and Ba in silicate rocks. REE and Ba were quantitatively separated from other elements by cation exchange column method. The chemical yield of each separation was monitored with Pr added to the sample powder before decomposition. The accuracy and precision were tested by repeated analyses of JB-1 and one analysis of BCR-1. In addition, it was found that REE distribution in a granitic rock powder was inhomogeneous and therefore special care must be taken for the sampling of granitic rock powders.     

Synthesis of novel 3-(α-arylhydrazono-1,3,4-oxadiazol-2-ylmethyl)-2-oxo-1,2-dihydroquinoxalines and their characteristic tautomerism between the hydrazone imine and diazenyl enamine forms

The reactions of 3-(α-arylhydrazono)hydrazinocarbonylmethyl-2-oxo-1,2-dihydroquinoxalines 1a,b with triethyl orthoesters resulted in the intramolecular cyclization to give the 3-(α-arylhydrazono-1,3,4-oxadiazol-2-ylmethyl)-2-oxo-1,2-dihydroquinoxalines 4a–d , but not the 1,2,4,5-tetrazepinylquinoxalines 5a–d . The cyclization mode into the 1,3,4-oxadiazole ring was confirmed by the alternate syntheses of 4a,c from the reactions of 3-(1,3,4-oxadiazol-2-ylmethylene)-2-oxo-1,2,3,4-tetrahydroquinoxalines 6a,b with o-chlorophenyl diazonium salts, respectively. Moreover, 4a–d exhibited an interesting tautomerism between the hydrazone imine form A and diazenyl enamine form B.     

Application of ferrous-chromate and iodometric titration for the determination of copper oxidation states in the superconductor YBa2Cu3Oy

Summary Oxidation-reduction titration methods, Fe²⁺-Cr₂C ₇ ^2– and I^–-S₂O ₃ ^2– , were applied to the determination of the oxidation state of copper in the superconductor YBa₂Cu₃O _y , and related compounds. The former method presented problems in the sample dissolution and titration steps. The dissolution of the sample in low concentrations of Fe⁺-phosphoric acid and Fe²⁺-perchloric acid takes place in two steps, the oxidation of Fe²⁺ to Fe³⁺ and the liberation of oxygen gas, when the liberation results in low analytical values for Cu⁺. In addition the coexistence of cuprous ion and acids induces the oxidation of ferrous ion by dissolved oxygen and air. The problems were resolved by dissolution in 0.1 mol/l Fe²⁺-phosphoric acid and titration in an argon atmosphere. The latter method gave good results by controlling the amounts of potassium chloride, the concentration of acetic acid, and by elimination of the dissolved oxygen in acetic acid solution. The results of the two titration methods coincided with each other.

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Anwendung der Eisen(II)-Chromat- und der iodometrischen Titration zur Bestimmung der Oxidationsstufe des Kupfers im Supraleiter YBa₂Cu₃O _y