X‐ray crystal structures and MMA polymerization of cadmium(II) complexes with bidentate pyrazole ligands: the formation of monomers or dimers as a function of a methyl substituent on the pyrazole and aniline rings

The reaction of CdBr₂·4H₂O with ancillary ligands, N,N‐bis(1H‐pyrazolyl‐1‐methyl)aniline ( L₁ ), N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐p‐methylaniline ( L₂ ), N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐3,5‐dimethylaniline ( L₃ ), N,N‐bis(3,5‐dimethyl‐1H‐pyrazolyl‐1‐methyl)aniline ( L₄ ) and N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐2,6‐dimethylaniline ( L₅ ) in ethanol yields novel Cd(II) bromide complexes, [L₁CdBr₂]₂ , [L₂CdBr₂]₂ , [L₃CdBr₂]₂ , [L₄CdBr₂] and [L₅CdBr₂] . The X‐ray crystal structures of [L₁CdBr₂]₂ , [L₂CdBr₂]₂ and [L₃CdBr₂]₂ reveal a bromo‐bridged dimeric species with crystallographic inversion symmetry. Conversely, [L₄CdBr₂] and [L₅CdBr₂] exist as monomeric complexes, presumably due to the steric hindrance between the methyl substituents of the two pyrazole groups in the ligand and cadmium centre for [L₄CdBr₂] , and crowding around the cadmium metal by methyl substituents on the aniline residue in the ligand for [L₅CdBr₂] . The geometry at each Cd(II) centre for [L₁CdBr₂]₂ , [L₂CdBr₂]₂ and [L₃CdBr₂]₂ is best described as a distorted trigonal bipyramid. A distorted trigonal bipyramid is achieved in [L₄CdBr₂] by coordinative interaction of the nitrogen atom of the aniline unit and the cadmium atom with a σ plane of symmetry, based on the bond length of Cd―N_aniline (2.759(7) Å). [L₅CdBr₂] exists with a distorted tetrahedral geometry involving non‐coordination of the nitrogen atom of aniline and the Cd centre, resulting in the formation of an eight‐membered chelate ring. The catalytic activity of monomeric, five‐coordinated [L₄CdBr₂] in the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60°C resulted in a higher molecular weight and a narrower polydispersity index (PDI) than those obtained with dimeric [L_nCdBr₂]₂ (L_n = L₁ , L₂ , L₃ ) or monomeric tetrahedral [L₅CdBr₂] . Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of growth pressure on the morphology evolution and doping characteristics in nonpolar a-plane GaN

Nonpolar a-plane GaN layers grown on r-plane sapphire substrates were examined by using a two-step growth process. The higher initial growth pressure for the nucleation layer resulted in the improved crystalline quality with lower density of both threading dislocations and basal stacking faults. This was attributed to the higher degree of initial roughening and recovery time via a growth mode transition from three-dimensional (3D) to quasi two-dimensional (2D) lateral growth. Using Hall-effect measurements, the overgrown Si doped GaN layers grown with higher initial growth pressure were found to have higher mobility. The scattering mechanism due to the dislocations was dominant especially at low temperature (<200 K) for the lower initial growth pressure, which was insignificant for the higher initial growth pressure. The temperature-dependent Hall-effect measurements for the Mg doped GaN with a higher initial growth pressure yielded the activation energy and the acceptor concentration to be 128 meV and 1.2 × 10¹⁹ cm⁻³, respectively, corresponding to about 3.6% of activation at room temperature. Two-step growth scheme with a higher initial growth pressure is suggested as a potential method to improve the performance of nonpolar a-plane GaN based devices.     

Study on the Constituents of Roots of Aceriphyllum rossii

A new stereoisomer of a tetrahydrofuranoid lignan, acerifuranoid A ( 1 ), and two new oleanane‐type triterpenoids, aceriphyllic acids J and K ( 2 and 3 ), were isolated from the roots of Aceriphyllum rossii. Their structures were elucidated on the basis of spectroscopic analyses and chemical evidence. These isolated compounds exhibited weak cytotoxic activity against various cancer cell lines with IC₅₀>150 μM .     

Time-resolved imaging of VUV emission from a He-Xe micro surfacedischarge

A direct observation of two-dimensional, time dependent behavior of 147 nm and 173 nm vacuum ultra violet emission from a single surface discharge type AC plasma display panel cell were obtained using a gated, image intensified charge-coupled device (ICCD). The images on the ICCD are formed by a pinhole. The two lines show similar spatial profile but quite different temporal behavior     

Impact of poly(ɛ‐caprolactone) architecture on the thermomechanical and shape memory properties

We report the synthesis of linear‐ and brush‐type poly(?‐caprolactone) (PCL) networks and investigate their thermal, mechanical, and shape memory behavior. Brush‐PCLs are prepared by ring‐opening metathesis polymerization (ROMP) of a norbornenyl‐functionalized ?‐caprolactone macromonomer (MM‐PCL) of different molecular weights. The linear analog, diacrylate end‐functionalized PCL (linear‐PCL), having comparable molecular weight of side chain of brush‐PCL is also synthesized. These polymers are thermally cured by a radical initiator in the presence of poly(ethylene glycol) diacrylate crosslinker. Thermal and linear viscoelastic properties as well as shape memory performance of the resulting PCL networks are investigated, and are significantly impacted by the PCL architecture. Therefore, our work highlights that tailoring macromolecular architecture is useful strategy to manipulate thermal, mechanical, and resulting shape memory properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3424–3433     

Solution processed fabrication of single wall carbon nanotubes thin film by electrohydrodynamic atomization deposition technique and its characterization

An effective method for the fabrication of thin film of single wall carbon nanotubes (SWCNT) using the electro-hydrodynamic atomization (EHDA) deposition technique was demonstrated. In this study, the SWCNT aqueous based dispersion ink was subjected to electrostatic atomization by using an EHDA deposition system. The ink flow visualization under the influence of electric field was performed and the operating EHDA parametric envelope of the ink was explored. Then the deposition of SWCNT through the EHDA process was carried out onto a metallic substrate at a fixed flow rate and corresponding applied voltage thereby achieving thickness ranging from ??70 to 130?nm by making multiple deposition passes. The microscopic inspection of the film was performed and thin film quality was examined by scanning electron microscope analysis. Finally, electrical behavior of the SWCNT film onto a metallic substrate through temperature dependent current-voltage measurements was investigated. The SWCNT film deposited onto the metallic substrate showed electrical conductivity of ??2.98?S/cm.