13C NMR and electron spin resonance analyses of the radical polymerization of diisopropyl itaconate

Radical polymerizations of dialkyl itaconates were performed in benzene at 50 °C. The ¹³C NMR spectra of the obtained polymers indicated that intramolecular chain‐transfer reaction had taken place more frequently in the polymerizations of itaconates with bulkier ester groups as follows: isopropyl (i‐Pr) > n‐butyl (n‐Bu) ≈ ethyl (Et) > methyl (Me). In addition to the ¹³C NMR analysis, an electron spin resonance (ESR) analysis was conducted for polymerizations of diisopropyl itaconate, the ESR spectra of which consisted of two kinds of resonances due to the radicals with different conformations. It was assumed that the difference in conformation was attributable to the stereosequences near the propagating chain end because the relative intensity ratios of the resonances varied with the magnitude of the intramolecular chain‐transfer reaction, which was accompanied by a decrease in the syndiotacticity of the obtained poly(diisopropyl itaconate)s. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4513–4522, 2002     

Fabrication of self-standing nanowires, nanodendrites, and nanofractal-like trees on insulator substrates with an electron-beam-induced deposition

Self-standing tungsten nanowires, nanodendrites, and nanofractal-like trees were fabricated on insulator (Al₂O₃) substrates with a process of electron-beam-induced decomposition in a transmission electron microscope. The conditions for fabricating different morphologies are described. The fabricated structures are characterized with high-resolution transmission electron microscopy and X-ray energy-dispersive spectroscopy. A high concentration of tungsten and a high crystallinity of the structure are confirmed. The growth process is discussed, involving charges produced on the surface of the substrate and the behavior of precursor molecules under electron-beam irradiation. The formation of these structures is considered to relate to nanoscaled unevenness of the charge distribution on the surface of the substrate, movement of charges to the convex surface of the substrate, and accumulation of charges at the tips of the grown structures. PACS 81.07.-b; 07.78.+s; 81.15.Gh; 81.16.-c     

π-Extended Thiadiazoles Fused with Thienopyrrole or Indole Moieties: Synthesis, Structures, and Properties

We report the syntheses, structures, photophysical properties, and redox characteristics of donor-acceptor-fused π-systems, namely π-extended thiadiazoles 1-5 fused with thienopyrrole or indole moieties. They were synthesized by the Stille coupling reactions followed by the PPh(3)-mediated reductive cyclizations as key steps. X-Ray crystallographic studies showed that isomeric 1b and 2b form significantly different packing from each other, and 1a and 4a afford supramolecular networks via multiple hydrogen bonding with water molecules. Thienopyrrole-fused compounds 1b and 2b displayed bathochromically shifted intramolecular charge-transfer (CT) bands and low oxidation potentials as compared to indole-fused analog 3b and showed moderate to good fluorescence quantum yields (Φ(f)) up to 0.73. In 3b-5b, the introduction of electron-donating substituents in the indole moieties substantially shifts the intramolecular CT absorption maxima bathochromically and leads to the elevation of the HOMO levels. The Φ(f) values of 3-5 (0.04-0.50) were found to be significantly dependent on the substituents in the indole moieties. The OFET properties with 1b and 2b as an active layer were also disclosed.     

Nematic conformation of oxyethylene spacers involved in main-chain liquid crystals

²HNMR measurements were performed on main-chain dimer and polymer liquid crystals (LC) having oxyethylene (OE) spacers -(OCH₂CH₂)_xO-(x=2, 3). The orientational as well as conformational characteristics of these molecules have been investigated in bulk and in a nematic solution. The OE spacer was found to take spatial arrangements characteristics of the nematic phase. The nematic conformation of the spacer remains nearly invariant over a wide range of temperature and concentration. In these analyses, the ratio of the deuterium quadrupolar splittings Δν/Δν^R (Δν: spacer and Δν^R: mesogenic unit) provided an important information regarding the spatial configuration of molecules in the LC state. The results obtained in this study are consistent with our previous conclusion drawn on a series of main-chain LC oligomers and polymers comprising n-alkane spacers -O(CH₂)_nO- (n=9, 10).     

Support Varieties for Modules Over Stacked Monomial Algebras

Let Λ be a finite-dimensional (D, A)-stacked monomial algebra. In this article, we give necessary and sufficient conditions for the variety of a simple Λ-module to be nontrivial. This is then used to give structural information on the algebra Λ, as it is shown that if the variety of every simple module is nontrivial, then Λ is a D-Koszul monomial algebra. We also provide examples of (D, A)-stacked monomial algebras which are not self-injective but nevertheless satisfy the finite generation conditions (Fg1) and (Fg2) of [4 Erdmann , K. , Holloway , M. , Snashall , N. , Solberg , Ø. , Taillefer , R. ( 2004 ). Support varieties for selfinjective algebras . K-Theory 33 : 67 – 87 .[Crossref] , [Google Scholar]], from which we can characterize all modules with trivial variety.     

Bending and springback theory of metal-polymer sandwich laminates

In this report an analysis is made of the behavior of sandwich beams in which the core polymer is laminated on both sides with surface metal sheets, each of which has a different thickness and mechanical properties when they are loaded with a uniform bending moment which is then released resulting in springback of the bent sandwich beam. It is assumed that the polymer behaves elastically because the bending strain in the core is small and its elastic limit is much larger than that of metals. Sandwich beams have various elastoplstic stess distributions when bent depending on the mutual relationships between their dimensions, the mechanical moduli, and the applied bending moment. Further, residual curvatures, shifting position of neutral axis, and residual stress distributions in sandwich beams variously elastoplastically stressed initially on the decrease of applied bending moment are analyzed.     

Dirichlet series obtained from the error term in the Dirichlet divisor problem

In this paper we consider the Dirichlet series obtained from the error term in the Dirichlet divisor problem. We shall prove their analytic continuations and determine the locations of poles. We shall also discuss the relation between our results and the conjecture of Lau and Tsang on the mean square estimate of the error term.