Materials Literature
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The enantiomeric excesses obtained during the epoxidation reactions of p-chlorostyrene or 1,2-dihydronaphthalene catalysed by two different series of chiral porphyrins are reported. An attempt is made to correlate the enantioselectivity with the steric hindrance generated by the straps of these catalysts. It is shown…
The behavior of chiral-nematic and isotropic phases of helical kappa-carrageenan in aqueous solution of sodium iodide was compared with that of the anisotropic biphasic phase that contains both these phases. On the basis of birefringence, rheology, chemical analysis, average molecular weight, and polydispersity index…
A main-chain nonracemic chiral liquid crystalline polymer was synthesized from ( R )-(−)-4‘-{ω-[2-( p -hydroxy- o -nitrophenyloxy)-1-propyloxy]-1-decyloxy}-4-biphenylcarboxylic acid. This polymer contained 10 methylene units in each chemical repeating unit and was abbreviated PET( R *-10). On the basis of differential…
Protonated forms of layered perovskites were derived from Aurivillius phases, Bi 2 ANaNb 3 O 12 (A = Sr or Ca), by the substitution of bismuth oxide sheets with protons via acid treatment. The conversion into the protonated forms was achieved easily using 6 M HCl at room temperature. Preservation of the structure of t…
The effect of γ-radiation on a perfluoroalkoxy (PFA) resin was examined using solid-state high-speed magic angle spinning (MAS) 19 F NMR spectroscopy. Samples were prepared for analysis by subjecting them to γ-radiation in the dose range 0.5−3 MGy at either 303, 473, or 573 K. New structures identified include new sat…
An investigation of side chain microphase separation within a single comb copolymer molecule containing chemically different A and B side chains has been carried out. Expressions for the transition point in a good ( ∼ N -3/8 ), marginal ( ∼ N -1/2 ), θ ( ∼ N -2/3 ), and poor ( ∼ N -1 ) solvent are derived both by a me…
Abstract A novel preparation approach for high‐performance polyimide gels that are swollen or have a jungle‐gym‐type structure is proposed. A new rigid and symmetric trifunctional amine, 1,3,5‐tris(4‐aminophenyl)benzene (TAPB), was synthesized as a crosslinker. Three different kinds of amic acid oligomers derived from…
Thermally activated mobility of clusters of interstitial atoms is an important factor driving microstructural evolution of materials under irradiation. Molecular dynamics simulations show that the statistics of one-dimensional Brownian motion of clusters is characterized by unusual correlated jumps spanning many inter…
Mixtures of Ln(SC(6)F(5))(3) and Ln(EPh)(3) (E = S, Se) react with elemental E to give chalcogen-rich clusters with fluorinated thiolate ancillary ligands. The structures of both (THF)(6)Yb(4)S(SS)(4)(SC(6)F(5))(2) and (THF)(6)Yb(4)Se(SeSe)(4)(SC(6)F(5))(2) have been established by low-temperature single-crystal X-ray…
New misfit cobaltites, containing lead and mercury, have been synthesized, [Pb 0.7 Sr 1.9 Co 0.4 O 3 ][CoO 2 ] 1.8 and [Pb 0.7 Hg 0.2 Sr 1.9 Co 0.2 O 3 ][CoO 2 ] 1.8 . Their structural study, using high resolution electron microscopy and X-ray powder diffraction, shows that the samples are perfectly homogeneous and co…
The structure and bonding in alpha and beta octamolybdate anions have been investigated using density functional methods. In general, good computational-experimental agreement for the geometrical parameters has been obtained. The electronic structure of the anions has been probed with molecular orbital and Mulliken-Ma…
Rare-earth-doped SiO2 colloids can be grown in a wet chemical procedure by adding the appropriate rare earth chloride to a solution of tetraethoxysilane, glacial acetic acid, and water. The size polydispersity of the particles can be controlled in a seeded growth process, and monodisperse Er3+-doped particles were gro…
Maleated polyethylene/silicate nanocomposite (PEMA/20A) and maleated polyethylene/SiO 2 composite (PEMA/SiO 2 ) were prepared by the melt compounding. Transmission electron microscopy and X-ray scattering results confirmed the exfoliation of the silicate layers (20A) throughout the maleated polyethylene (PEMA) matrix,…
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTSANS and Cryo-TEM Study of Self-Assembled Diblock Copolypeptide Hydrogels with Rich Nano- through Microscale MorphologyDarrin J. Pochan, Lisa Pakstis, Bulent Ozbas, Andrew P. Nowak, and Timothy J. DemingView Author Information Mater…
Experimental control of block copolymer segregation is ideally achieved by varying temperature, but in practice, the range of segregation is very restricted. A far greater range can be accessed by diluting the block copolymer melt with a solvent, assuming the mixture obeys the so-called dilution approximation. We exam…
UV excitation of ${\mathrm{Ce}}^{3+}$-doped ${\mathrm{Ca}}_{2}{\mathrm{Al}}_{2}{\mathrm{SiO}}_{7}$ melilite crystals produces long-lasting phosphorescence $(1\ensuremath{-}{10}^{3} \mathrm{s})$ from ${\mathrm{Ce}}^{3+}$ ions in addition to the intrinsic ${\mathrm{Ce}}^{3+}$ luminescence with a lifetime of 40 ns. The d…
Polymers containing coumarin and Ru(BpyMe 2 ) 3 2+ chromophores were synthesized using a grafting approach and also a copolymerization approach. It was found that the solubility of polymers made from Ru-containing monomers was higher than that observed for comparable polymers obtained by grafting of Ru complexes onto…
Surface-tethered triblock copolymers composed of poly(methyl acrylate), poly(methyl methacrylate), and poly(2-hydroxyethyl methacrylate) were grown from gold substrates by a series of atom transfer radical polymerizations at ambient temperature. GPC determinations of the molecular weights of desorbed triblock homopoly…
Covalently bonded layered silicates/polyimide (BTDA-ODA) nanocomposites have been synthesized from γ-(aminopropyl)triethoxysilane (APTS) grafted kenyaite and poly(amic acid). The existence of covalent bonds between APTS and silicates and between APTS and the dianhydride end groups of the polymer have been confirmed by…
Two novel B 3 monomers, tri(phthalic anhydride) and tri(phthalic acid methyl ester), were synthesized. Hyperbranched polyimides were prepared by A 2 + B 3 polymerizations of (a) 1,4-phenylenediamine (A 2 ) and tri(phthalic anhydride) (B 3 ) (method A) and (b) 1,4-phenylenediamine (A 2 ) and tri(phthalic acid methyl es…