Synthesis and characterization of new segmented polyurethanes with side‐chain,liquid‐crystalline chain extenders

Liquid‐crystalline, segmented polyurethanes with methoxy–biphenyl mesogens pendant on the chain extender were synthesized by the conventional prepolymer technique and esterification reaction. Two, side‐chain, liquid‐crystalline (SCLC) polyurethanes with mesogens having spacers of six and eight methylene units were prepared. The structures of the mesogenic units and SCLC polyurethanes were confirmed by Fourier transform infrared spectroscopy and ¹H NMR. Polymer properties were also examined by solubility tests, water uptakes, and inherent viscosity measurements. Differential scanning calorimetry studies indicated that the transition temperature of the isotropic to the liquid‐crystalline phase decreased with increasing spacer length. Wide‐angle X‐ray diffraction (WAXD) studies revealed the existence of liquid‐crystalline phases for both SCLC polyurethanes. Polarized optical microscopic investigations further confirmed the thermotropic liquid‐crystalline behaviors and nematic mesophases of both samples. Thermogravimetric analysis displayed better thermal stabilities for both SCLC polymers and indicated that the presence of mesogenic side chains may increase the thermal stability of segmented polyurethanes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 290–302, 2004     

Intramolecular energy transferable (2,2‐diphenylvinyl)phenyl substituted poly(p‐phenylenevinylene) derivative with efficient photoluminescence and electroluminescence

A poly(p‐phenylenevinylene) (PPV) derivative containing a bulky (2,2‐diphenylvinyl)phenyl group in the side chain, EHDVP‐PPV, was synthesized by Gilch route. The reduced tolane‐bisbenzyl (TBB) defects, as well as the structure of the polymer, was confirmed by various spectroscopic methods. The intramolecular energy transfer from the (2,2‐diphenylvinyl)phenyl side group to the PPV backbone was studied by UV‐vis and photoluminescence (PL) of the obtained polymer and model compound. The polymer film showed maximum absorption and emission peaks at 454 and 546 nm, respectively, and high PL efficiency of 57%. A yellow electroluminescence (λ_max = 548 nm) was obtained with intensities of 6479 cd/m² when the light‐emitting diodes of ITO/PEDOT/EHDVP‐PPV/LiF/Al were fabricated. The maximum power efficiency of the devices was 0.729 lm/W with a turn‐on voltage of 3.6 V. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5636–5646, 2004     

Composite Silica Particles Using a Mixture of Organosilane Monomers

Composite silica particles were synthesized by a two-step (acid-base) process in an aqueous solution with a mixture of organoalkoxysilane monomers. The two-step process separates the hydrolysis and condensation procedures to easily control condensation rate. In this study, the silane monomers used were phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), methyltrimethoxysilane (MTMS), and tetraethyl-orthosilicate (TEOS). The physical properties of the resultant composite particles were investigated with the change in the molar ratio of monomers. The size of the particles increased with increasing the molar ratio of R_aSi(OR)₃/R_bSi(OR)₃ or R_aSi(OR)₃/TEOS (R_a: phenyl; R_b: vinyl, methyl).     

Synthesis and characterization of soluble polyimides containing trifluoromethyl groups in their backbone

A series of polyimides were synthesized from 2,2‐Bis(3,4‐dicarboxyphenyl)hexafluoropropane, 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane, and 4,4′‐oxydianiline by chemical imidization. The effects of the diamine ratios on the properties of the films were evaluated through the study of their thermal, electrical, and morphological properties. All the polymers exhibited better solubility in most of the organic solvents and hence were easily processable. Polyimides with more 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane exhibited better solubility and a low refractive index, which is highly desired for microelectronic applications. The dielectric constant and birefringence were strongly dependent on the fluorine content. With an increase in the fluorine substitution, both the dielectric constant and birefringence decreased. All the polymers exhibited high thermal stability (>400 °C). The absence of crystalline melting in differential scanning calorimetry and broad wide‐angle X‐ray diffraction patterns revealed the amorphous nature of the polymers, which was due to the presence of bulky CF₃ groups and hinged ether linkages of the diamine component. The residual stress values decreased with an increase in the 4,4′‐oxydianiline content, and the results were in agreement with the dielectric constant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4303–4312, 2004     

Combined effects of clay modifications and compatibilizers on the formation and physical properties of melt‐mixed polypropylene/clay nanocomposites

The melt mixing technique was used to prepare various polypropylene (PP)‐based (nano)composites. Two commercial organoclays (denoted 20A and 30B) served as the fillers for the PP matrix, and two different maleated (so‐called) compatibilizers (denoted PP‐MA and SMA) were employed as the third component. The results from X‐ray diffraction (XRD) and transmission electron microscope (TEM) experiments revealed that 190 °C was an adequate temperature for preparing the nanocomposites. Nanocomposites were achieved only if specific pairs of organoclay and compatibilizer were simultaneously incorporated in the PP matrix. For example, PP/20A(5 wt %)/PP‐MA(10 wt %) and PP/30B(5 wt %)/SMA(5 wt %) composites exhibited nanoscaled dispersion of 20A or 30B in the PP matrix. Differential scanning calorimetry (DSC) results indicated that the organoclays served as nucleation agents for the PP matrix. Generally, their nucleation effectiveness increased with the addition of compatibilizers. The thermal stability enhancement of PP after adding 20A was confirmed with thermogravimetric analysis (TGA). The enhancement became more evident as a suitable compatibilizer was further added. However, for the 30B‐included composites, thermal stability enhancement was not evident. The dynamic mechanical properties (i.e., storage modulus and loss modulus) of PP increased as the nanocomposites were formed; the properties increment corresponded to the organoclay dispersion status in the matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4139–4150, 2004     

基于图像处理技术的束流剖面监视系统

 介绍了在兰州重离子加速器上利用荧光靶图像获取装置测量并计算束流剖面参数的方法，并建立了图像获取、处理、束流参数计算的实时测量软件系统。该系统具有可靠性好、测量直观、界面友好等优点。     

掺杂偶氮苯聚合物光致异构Z扫描测量及其理论解释

用He_Ne激光对掺有偶氮苯聚合物DR 13的PMMA薄膜样品进行Z扫描研究 ,发现其折射率改变量与光强的关系存在着饱和效应 ,且线偏振光引起的折射率改变明显大于圆偏振光引起的折射率改变 .对于这些现象 ,用光致异构的角烧孔机理进行解释     

Kinetic Studies on the Reaction of Sodium Hexa-cyanoferrate(II) Complex with Peroxydisulfate Anion

Introduction In the previous studies on the oxidation reaction,peroxydisulfate was widely used as an oxidizingagent.1-5 One of the advantages of this oxidant lies in itsstability in a wide range of pH values. The reaction be-tween Fe(CN)5L3- (L=N-aromatic heterocyclic li-gands) and S2O8 2- has been proved to proceed throughan outer-sphere electron transfer mechanism.5 For a re-action [(Eq. (1)] to be under an outer-sphere mechanismthe steps involved are the formation of a reactant …     

Metabolites of A Novel Antibiotic Bitespiramycin in Rat Urine and Bile

A sensitive analytical method to identify active metabolites of bitespiramycin in rat urine and bile was developed by liquid chromatography-electrospray ionization tandem mass spectrometry(LC/ESI-MS^n).Bitespiramycin and its major active metabolites in rat urine and bile were isolated and identified as M1 serial(spiramycin Ⅰ，Ⅱ，Ⅲ),M2 serial(platenomycin A1,josamycin and leucomycin A1) and M3 serial(deisovalerylplatenomycin A1,deisovaleryljosamycin,deisovalerylleucomycin A1).     

Baker＇s Yeast Mediated Reduction of Optically Active Diketone

Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products.