Formation of defect structures in Au-polysilane interfaces probed by low energy positron beams

Formation and accumulation of defect structures at interfaces between polysilanes and vacuum-evaporated gold (Au) electrodes are discussed quantitatively by low energy positron annihilation spectroscopy. The size distribution of the defects at the interface is analyzed based on the values of ortho-positronium (o-Ps) lifetime (τ₃), and no effect of the evaporation process is observed in the polymer films. The intensity of o-Ps (I₃) indicates no considerable change before and after Au evaporation on dialkyl-substituted polysilanes, however, the values of I₃ is increased ∼20% in phenyl-substituted polysilane (PMPS) by the evaporation. The I₃ dependence on incident positron energy suggests the formation of the defects not only at an Au-PMPS interface but also in PMPS bulk phase as deep as 400 nm from the interface. Phenyl ring dissociation from the polymer backbone will play a significant role in the selective formation of the defects in PMPS. This is the first report on the direct measurement of defect structures at conjugated polymer-metal interface with non-destructive way, implying that electrode fabrication by vacuum evaporation affects the solid state structure of polymers.     

High‐Yield Electrochemical Production of Formaldehyde from CO2 and Seawater

The catalytic, electrocatalytic, or photocatalytic conversion of CO₂ into useful chemicals in high yield for industrial applications has so far proven difficult. Herein, we present our work on the electrochemical reduction of CO₂ in seawater using a boron‐doped diamond (BDD) electrode under ambient conditions to produce formaldehyde. This method overcomes the usual limitation of the low yield of higher‐order products, and also reduces the generation of H₂. In comparison with other electrode materials, BDD electrodes have a wide potential window and high electrochemical stability, and, moreover, exhibit very high Faradaic efficiency (74 %) for the production of formaldehyde, using either methanol, aqueous NaCl, or seawater as the electrolyte. The high Faradaic efficiency is attributed to the sp³‐bonded carbon of the BDD. Our results have wide ranging implications for the efficient and cost‐effective conversion of CO₂.     

Effect of the substrate temperature and deposition rate on the initial growth of thin lithium niobate-tantalate films deposited from a thermal plasma

Thin lithium niobate-tantalate (LiNb_0.5Ta_0.5O₃) films are studied at the initial stage of deposition from a thermal plasma. The effect of two deposition parameters (the substrate temperature and the deposition rate) on the film morphology, the film crystallinity, and the density of nuclei growing on a (0001) sapphire substrate are investigated. It is shown that the crystalline structure and roughness of a film are determined, for the most part, in the initial growth stage and therefore depend directly on both parameters. At the optimum temperatures and growth rates for obtaining good characteristics of (0006) texture, crystallinity, and surface roughness of the films, the film nuclei on the substrate have a high density and good epitaxial orientation to it. If the growth conditions are not optimum, the islands are either amorphous or have a low density on the substrate surface. The nucleation activation energy is observed to decrease as the deposition rate increases, which supports the assumption that the species that are active in film deposition are “hot” clusters forming in an oxygen-argon plasma in the immediate vicinity of the substrate.     

Chiral synthesis of the ABC-ring system of quinocarcin

Stereoselective synthesis of an enantiomeric pair of the ABC-ring system of quinocarcin(1), a notable antitumor antibiotic, could be achieved in> 95%ee by utilizing each enantiomer of 4-O-benzyl-2,3-O-isopropylidene-threose as a chiral auxiliary and featuring novel diastereoselective reduction of the 1,3-disubstituted isoquinoline as a key step.     

Selective single monomer addition in living cationic polymerization: Sequential double end‐functionalization in combination with capping agent

Amine‐functionalized and amine‐carboxylate double‐functionalized polymers ( I and II , respectively) have been synthesized by a selective single addition of a protected 2‐aminoethyl vinyl ether (BocVE) {CH₂ = CH[OCH₂CH₂N(Boc)₂]; Boc = t‐butoxycarbonyl} onto a living cationic poly(n‐butyl vinyl ether) [poly(NBVE)] initiated with the SnCl₄/n‐Bu₄NCl system: ( I ) ‐(NBVE)_n‐ CH₂CH(OCH₂CH₂NH₂)‐H; ( II ) ‐(NBVE)_n‐CH₂CH(OCH₂CH₂NH₂)‐CH₂CO₂H. The single addition was examined with a set of alkene monomers less reactive than NBVE, including BocVE, 2‐chloroethyl vinyl ether, 2‐vinyloxyethylphtalimide, and styrene (St). Upon addition of 10 molar excess of these alkenes onto the living ends, only BocVE led to the intended single adduct, and this was attributed to a chelating interaction of the two carboxylate groups in the terminal BocVE unit with the growing poly(NBVE) terminal, thus sterically hampering further propagation. A simple acid‐catalyzed Boc‐deprotection led to the amino‐functionalized version I . Alternatively, an additional quenching the BocVE‐capped living end (the precursor of I ) with sodium malonate, followed by double deprotection of the Boc and the malonate groups gave the double‐functionalized version II . The selective addition of a single monomer molecule is thus a new method for addressable or site‐specific introduction of functional groups along polymer chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3375–3381, 2010     

Understanding the catalytic activity of single‐chain polymeric nanoparticles in water

The structuring role of benzene‐1,3,5‐tricarboxamide (BTA) groups for the catalytic activity of single chain polymeric nanoparticles in water was investigated in the transfer hydrogenation of ketones. To this end, a set of segmented, amphiphilic copolymers was prepared, which comprised oligo(ethylene glycol) side chains to impart water solubility, BTA and/or lauryl side chains to induce hydrophobicity and diphenylphosphinostyrene (SDP) units in the middle part as a ligand to bind a ruthenium catalyst. All copolymers were obtained by reversible addition‐fragmentation chain transfer (RAFT) polymerization and showed low dispersities (M_w/M_n = 1.23–1.38) and controlled molecular weights (M_n = 44–28 kDa). A combination of circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) showed that all copolymers fold into a single chain polymeric nanoparticles (SCPNs) as a result of the helical self‐assembly of the pendant BTA units and/or hydrophilic–hydrophobic phase separation. To create catalytic sites, RuCl₂(PPh₃)₃ was incorporated into the copolymers. The Cotton effects of the copolymers before and after Ru(II) loading were identical, indicating that the helical self‐assembly of the BTA units and the complexation of SDP ligands and Ru(II) occurs in an orthogonal manner. DLS revealed that after Ru(II) loading, SDP‐bearing copolymers retained their single chain character in water, while copolymers lacking SDP units clustered into larger aggregates. The Ru(II) loaded SCPNs were tested in the transfer hydrogenation of cyclohexanone. This study reveals that BTA induced stack formation is not crucial for SCPN formation and catalytic activity; SDP‐bearing copolymers folded by Ru(II) complexation and hydrophobic pendants suffice to provide hydrophobic, isolated reaction pockets around Ru(II) complexes. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 12–20     

Semi-micro-monolithic columns using macroporous silica rods with improved performance

Monolithic silica columns in semi-micro-format have been synthesized using poly(acrylic acid) as a phase-separation inducer via a sol–gel route. The absence of a thick skin layer accompanied by deformation of the micrometer-sized gelling skeletons on the outermost part of the macroporous silica rod contributed to improve the efficiency of monolithic silica columns as thick as 2.4 mm in diameter. The kinetic plot analysis revealed that monolithic silica columns with macropore diameter of 1 μm and skeleton thickness of 1 μm with decreased macroporosity behave similarly to columns packed with 3 μm particles with slightly lower back pressure.