Heat of Formation for LiMyMn2−yO4 (M=Co,Cr, Li,Mg, Ni) Spinel Solid Solution

The enthalpy of formation for LiM_yMn_2–yO₄ (M=Co, Cr, Li, Mg, Ni) was measured by a Tian-Calvet type high temperature isothermal microcalorimeter. The standard enthalpy of formation for LiMn₂O₄ at 876 K was evaluated to be H_f⁰=–1404.2±6.4 kJ mol^–1. The partial substitution of Co and Ni for Mn decreased the absolute H_f⁰ value, while that of Cr and Mg for Mn increased the absolute H_f⁰ value. In the case of the partial substitution of Li for Mn, no marked change in H_f⁰ could be observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Homochiral column structure of rac- and lambda-tris(ethylenediamine)cobalt(III) cyclotriphosphate dihydrate in crystal structures and cation-anion association in aqueous solution

rac- and Lambda-tris(ethylenediamine)cobalt(III) cyclotriphosphate dihydrate with the chemical formulas rac-[Co(en)(3)]P(3)O(9).2H(2)O (1) and Lambda-[Co(en)(3)]P(3)O(9).2H(2)O (2) were synthesized, and their crystal structures were determined by single-crystal X-ray analyses. In 1, the cationic complex molecule [Co(en)(3)](3+) with the Delta or Lambda enantiomer and cyclotriphosphate anion are alternately arrayed and connected by multiple hydrogen bonds to form a homochiral column structure. Adjacent homochiral columns with different chirality for 1 are connected by intercolumn hydrogen bonds through P(3)O(9)(3)(-) anions, as the bridging groups, to form a tetrameric cyclic cylindrical structure, while the adjacent columns with the same chirality are connected for 2 to form the cyclic cylindrical structure. All 6 amino groups per [Co(en)(3)](3+) participate in the formation of 12 hydrogen bonds, in which 8 hydrogen bonds contribute to the construction of a homochiral column and the remaining 4 hydrogen bonds contribute to the intercolumn interactions. The circular dichroism spectrum of the aqueous solution of Lambda-[Co(en)(3)](3+) changes drastically when excess P(3)O(9)(3)(-) is added, and this change is explained by ion-pair formation. The thermodynamic association constant of [Co(en)(3)](3+) with P(3)O(9)(3)(-), calculated from the conductivity data, was log K = 4.26 at 25 degrees C.     

Asymmetric polymerization of N‐substituted maleimides with chiral oxazolidine–organolithium

Asymmetric anionic homopolymerizations of achiral N‐substituted maleimides (RMI) were performed with lithium 4‐alkyl‐2,2‐dialkyloxazolidinylamide. All obtained polymers were optically active, exhibiting opposite optical rotation to that of a corresponding oxazolidinyl group at the terminal of the main chain. This suggests that opposite optical rotation to the corresponding chiral oxazolidine was induced to the polymer main chain. In the polymerization using a fluorenyllithium (FlLi)–oxazolidine complex, the obtained polymer with a fluorenyl group at the polymer end showed a negative specific rotation. This also suggests that asymmetric induction took place in the polymer main chain. The asymmetric induction was supported by the circular dichroism (CD) and GPC analysis with polarimetric detector. Optical activity of the polymer was attributed to different contents of (S,S) and (R,R) structures formed from threo‐diisotactic additions, as supported by the ¹³C‐NMR spectra of the polymers and the model compounds. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 473–482, 1999     

Recent lean NOx catalyst technologies for automobile exhaust control

The current status of our development work on lean NO_x catalysts for application to future gasoline and diesel engines is described. As a result of further improvements in fuel economy, the temperature of exhaust gas will be lower and there will be smaller quantities of hydrocarbons (HCs) in the exhaust of future engines. Therefore, it is necessary to improve the activity of lean NO_x catalysts at lower temperatures and achieve higher selectivity of the NO_x–HC reaction. Utilizing precious metal catalysts is one effective way of improving catalyst activity at lower temperatures, and HC adsorption and reforming are two key technologies for improving the catalyst selectivity for the NO_x–HC reaction.     

Structure and properties of polypropylene crystallized from the glassy state

Glassy isotactic propylene (PP) films of thickness up to 0.3 mm were obtained by an ultraquenching technique. The structure and properties of the as-quenched and subsequently crystallized samples were characterized by various techniques. Electron microscopy indicates the glass has no structure larger than 25 Å. X-ray diffraction shows PP crystallizes from the glass into a smectic structure at ca. ?20°C and then transforms to monoclinic microcrystals at ca. 40°C; a nodular structure (80 to 100 Å in diameter) was observed on the surface. The transformation temperature increases with the film thickness. Annealing above the α-relaxation temperature results in an increase in the nodule size. A correspondence was found between the diameter of the nodules observed on the surface and long spacings obtained by small-angle X-ray scattering from the bulk. Dynamic mechanical spectra show the presence of two relaxation-like peaks at ca. ?10°C and 10°C for the as-ultraquenched samples. X-ray scattering, differential scanning calorimetry (DSC), and torsion pendulum measurements show PP crystallizes from the glass at a temperature, depending on the rate of heating, that corresponds to the lower relaxation peak temperature.     

Evaluation of polycarbonate substrate hologram recording medium regarding implication of birefringence and thermal expansion

In this paper, we evaluate photopolymer media using a polycarbonate (PC) substrate. In holographic data storage medium, substrates that sandwich the photopolymer material are needed to protect the photopolymer material against exogenous shock and open air. An optical glass such as BK-7 is normally used as a substrate, but a PC substrate has a cost advantage and is easy to fabricate compared with optical glass. For holographic recording and reading, however, the high birefringence and high thermal expansion of a PC substrate are significant problems. First, we analyze the degree of degradation of output power by the polarization change and estimate the threshold value of birefringence to record hologram normally. Next, we estimate the temperature tolerance of hologram readout with polycarbonate substrate hologram medium. These analyses results indicate the possible usage of the PC substrate as holographic recording media.     

Anisotropy of dielectric relaxation in crystal form II of poly(vinylidene fluoride)

The anisotropy of the crystalline relaxation (α relaxation) in oriented poly(vinylidene fluoride) in crystal form II has been studied. The dielectric increment Δε is analyzed on the basis of the two-site model. A linear relation between Δε/χξ and cos²θ is obtained, where χ is the degree of crystallinity, ξ is the ratio of the internal field to the applied field, and θ is the angle between the applied electric field and the molecular axis. The dipole moment changes direction only along the molecular axis in the relaxation in crystal form II; the molecular motion cannot be explained by chain rotation around the molecular axis. Possible models for the α relaxation are proposed: change in conformation with internal rotation can occur in the crystalline chains, and defects in the crystalline regions play an important role in the α relaxation.