Synthesis of cellulose carbamate by supercritical CO2-assisted impregnation: Structure and rheological properties

Cellulose carbamate, an environmentally friendly material presents an interesting alternative to petroleum-based polymers because of its renewable, biodegradable, biocompatible nature and its solubility in conventional solvents. In synthesis process of cellulose carbamate, urea was firstly impregnated into the cellulose pulp by supercritical CO₂(scCO₂), followed by the esterification of cellulose. The structure of cellulose carbamate was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The rheological properties of these cellulose carbamates in 9% sodium hydroxide solution were investigated, using a range of the nitrogen content, concentrations and shear rates.     

Electroless deposition of open-end Cu nanotube arrays

Cu nanotube arrays were fabricated by electroless deposition using porous anodic aluminium oxide membranes as templates. This was accomplished by a four-step procedure, i.e. pore-wall modification, polishing treatment, sensitization-activation and electroless deposition. The as-synthesized Cu nanotubes possess controllable inner diameter and open ends.     

Structure for a graph with average genus

In [2], Chen et al. showed that the average genus for a graph of maximum degree at most 3 is at least 1/2 its maximum genus. In this paper, the structure for a graph of maximum degree at most 3 with average genus equal to 1/2 its maximum genus is described. Furthermore, LetH be a subgraph ofG and γ_avg(G) = γ_avg(H). It’s shown thatG can be obtained by a series operations of type I and II onH.     

Microstructure and wear properties of laser clad Cuss/Cr5Si3 metal silicide composite coatings

Wear resistant Cu-based solid solution (Cu_ss) toughened Cr₅Si₃ metal silicide composite coatings were fabricated on austenitic stainless steel AISI321 by laser cladding process. Due to the rapidly solidified microstructural characteristics and the excellent toughening effect of Cu_ss on Cr₅Si₃, the Cu_ss/Cr₅Si₃ coatings have outstanding wear resistance and low coefficient of friction under room temperature dry sliding wear test conditions coupling with hardened 0.45% C steel.     

具有突变结构开放腔的矩阵分析

利用模式展开与场匹配原理，建立了突变波导的散射矩阵(S参数矩阵)，在此基础上分析研究了具有突变结构的波导开放式谐振腔，并由矩阵级联建立了开放腔总的S参数矩阵.通过Matlab编制计算程序对具有多级突变结构的开放式输出腔进行了数值计算和分析，并通过与实验数据和软件模拟的结果比较对该方法得到的数据结果进行了验证. 关键词： 回旋管 开放式谐振腔 突变结构 S参数矩阵     

Synthesis and light emitting properties of polyacetylenes having pendent fluorene groups

Five novel fluorene‐containing polymers, poly[(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA1 ), poly[(1‐pentyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene) ( PFA2 ), poly[1‐decyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA3 ), poly[1‐phenyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA4 ), and poly[1‐(3,4‐difluorophenyl)‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA5 ) were synthesized by the polymerization of the corresponding fluorene‐substituted acetylenic monomers ( M1–M5), using WCl₆, MoCl_5, and TaCl₅ as catalysts and n‐Bu₄Sn as a cocatalyst. The synthesized polymers were thermally stable and readily soluble in common organic solvents. The degradation temperatures for a 5% weight loss of the polymers were ∼352–503 °C under nitrogen. PFA1–PFA5 show emission peaks from 402 to 590 nm. Besides, their electroluminescent properties were studied in heterostructure light‐emitting diodes (LEDs), using PFA2–PFA5 as an emitting layer. The PFA5 device revealed an orange‐red emission peak at 602 nm with a maximum luminescence of 923 cd/m² at 8 V. A device with the ITO/PEDOT/ a mixture of PFA2 (98 wt %) and PFA5 (2 wt %)/Ca/Al showed near white emission. Its maximum luminance and current efficiency are 450 cd/m² at 15 V and 1.3 cd/A, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 519–531, 2006     

Chemically modified proton‐conducting membranes based on sulfonated polyimides: Improved water stability and fuel‐cell performance

A series of branched/crosslinked sulfonated polyimide (B/C‐SPI) membranes were prepared and evaluated as proton‐conducting ionomers based on the new concept of in situ crosslinking from sulfonated polyimide (SPI) oligomers and triamine monomers. Chemical branching and crosslinking in SPI oligomers with 1,3,5‐tris(4‐aminophenoxy)benzene as a crosslinker gave the polymer membranes very good water stability and mechanical properties under an accelerated aging treatment in water at 130 °C, despite their high ion‐exchange capacity (2.2–2.6 mequiv g^?1). The resulting polymer electrolytes displayed high proton conductivities of 0.2–0.3 S cm^?1 at 120 °C in water and reasonably high conductivities of 0.02–0.03 S cm^?1 at 50% relative humidity. In a single H₂/O₂ fuel‐cell system at 90 °C, they exhibited high fuel‐cell performances comparable to those of Nafion 112. The B/C‐SPI membranes also displayed good performances in a direct methanol fuel cell with methanol concentrations as high as 50 wt % that were superior to those of Nafion 112. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3751–3762, 2006     

Sulfonated poly(aryl ether ether ketone ketone)s containing fluorinated moieties as proton exchange membrane materials

A series of sulfonated poly(aryl ether ether ketone ketone)s statistical copolymers with high molecular weights were synthesized via an aromatic nucleophilic substitution polymerization. The sulfonation content (SC), defined as the number of sulfonic acid groups contained in an average repeat unit, could be controlled by the feed ratios of monomers. Flexible and strong membranes in sodium sulfonate form could be prepared by the solution casting method, and readily transformed to their proton forms by treating them in 2 N sulfuric acid. The polymers showed high T_gs, which increased with an increase in SC. Membranes prepared from the present sulfonated poly(ether ether ketone ketone) copolymers containing the hexafluoroisopropylidene moiety (SPEEKK‐6F) and copolymers containing the pendant 3,5‐ditrifluoromethylphenyl moiety (SPEEKK‐6FP) had lower water uptakes and lower swelling ratios in comparison with previously prepared copolymers containing 6F units. All of the polymers possessed proton conductivities higher than 1 × 10^?2 S/cm at room temperature, and proton conductivity values of several polymers were comparable to that of Nafion at high relative humidity. Their thermal stability, oxidative stability, and mechanical properties were also evaluated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2299–2310, 2006     

Novel photoswitching dithienylethenes with ferrocene units

Two novel dithienylethenes with ferrocene units were synthesized by Wittig reaction. The structure of 2a has been established by X‐ray diffraction studies. They could reversibly interconvert between two thermally stable forms, an open and a closed one, using light of different wavelengths as triggers. Copyright © 2006 John Wiley & Sons, Ltd.     

高纯金属镨中痕量稀土杂质的电感耦合等离子体原子发射光谱分析及光谱干扰的校正

本文提出了PGS-2型平面光栅光谱仪(色散率0.18纳米,二级光谱)与PlasmaTherm ICP-5000D射频发生器联用,乙醇预去溶方式进样,同时直接测定高纯金属镨中5个痕量稀土杂质元素的方法。并讨论了基体浓度对检出限的影响以及光谱干扰及其校正方法。当样品溶液中镨的浓度为5毫克/毫升时,测定下限分别为镧、钕和钐0.002%,铈0.003%和钇0.0005%。获得了良好的实验结果,其相对标准偏差为1.2-6.2%。