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91.
Navzer D. Sachinvala David L. Winsor Othman Hamed Walter P. Niemczura Karol Maskos Tyrone L. Vigo Noelie R. Bertoniere 《先进技术聚合物》2002,13(6):413-427
Cellulose ( 1 ) was converted for the first time to 6‐phenyl‐6‐deoxy‐2,3‐di‐O‐methylcellulose ( 6 ) in 33% overall yield. Intermediates in the five‐step conversion of 1 to 6 were: 6‐O‐tritylcellulose ( 2 ), 6‐O‐trityl‐2,3‐di‐O‐methylcellulose ( 3 ), 2,3‐di‐O‐methylcellulose ( 4 ); and 6‐bromo‐6‐deoxy‐2,3‐di‐O‐methylcellulose ( 5 ). Elemental and quantitative carbon‐13 analyses were concurrently used to verify and confirm the degrees of substitution in each new polymer. Gel permeation chromotography (GPC) data were generated to monitor the changes in molecular weight (DPw) as the synthesis progressed, and the compound average decrease in cellulose DPw was ~ 27%. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the decomposition of all polymers. The degradation temperatures ( °C) and percent char at 500 °C of cellulose derivatives 2 to 6 were 308.6 and 6.3%, 227.6 °C and 9.7%, 273.9 °C and 30.2%, 200.4 °C and 25.6%, and 207.2 °C and 27.0%, respectively. The glass transition temperature (Tg) of6‐O‐tritylcellulose by dynamic mechanical analysis (DMA) occurred at 126.7 °C and the modulus (E′, Pa) dropped 8.9 fold in the transition from ?150 °C to + 180 °C (6.6 × 109 to 7.4 × 108 Pa). Modulus at 20 °C was 3.26 × 109 Pa. Complete proton and carbon‐13 chemical shift assignments of the repeating unit of the title polymer were made by a combination of the HMQC and COSY NMR methods. Ultimate non‐destructive proof of carbon–carbon bond formation at C6 of the anhydroglucose moiety was established by generating correlations between resonances of CH26 (anhydroglucose) and C1′, H2′, and H6′ of the attached aryl ring using the heteronuclear multiple‐bond correlation (HMBC) method. In this study, we achieved three major objectives: (a) new methodologies for the chemical modification of cellulose were developed; (b) new cellulose derivatives were designed, prepared and characterized; (c) unequivocal structural proof for carbon–carbon bond formation with cellulose was derived non‐destructively by use of one‐ and two‐dimensional NMR methods. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
92.
Seik Weng Ng Abdul Hamid Othman Sri Nurestri Abdul Malek 《Journal of chemical crystallography》1994,24(5):331-335
1-(2-Hydroxyphenyl)-3-phenyl-1,3-propanedione crystallizes in the triclinic space group
(a=5.4233(5),b=13.910(1),c=17.036(1) Å, =68.311(6), =80.854(7), =78.760(8)°) as two independent enolic tautomers in which the hydroxyl and phenolic protons are hydrogen bonded to the ketonic oxygen atom. The structure was refined toR=0.039 for 2085I3(I) reflections. 1-(1,3-Benzodioxol-5-yl)-3-(2,4-dimethoxyphenyl)-1,3-propanedione, which belongs to the triclinic
space group (a=7.3990(7),b=8.1239(5),c=14.004(1) Å, =86.673(6). =88.574(7), =64.885(7)°) also exists in the enolic form. The structure was refined toR=0.040 for 1564I3(I) reflections. 相似文献
93.
This paper reports photoelectrical properties of (As30Sb15Se55)100?xTex amorphous chalcogenide films (0 ? x ? 12.5 at.%) through measurements of ‘steady state’ and ‘transient’ photocurrents. The composition dependence of the steady state photocurrent at room temperature shows that the photoconductivity increases while the photosensitivity decreases with increasing Te content. A study of photoconductivity of (As30Sb15Se55)100?xTex at different levels of light intensity reveals that, the photoconductivity increases exponentially with increase in light intensity. The Photocurrent (Iph) when plotted against light intensity (G) follows a power law (Iph = Gγ) the exponent γ for (As30Sb15Se55)100?xTex films has been found nearly 0.5 suggesting bimolecular recombination. The transient photoconductivity shows that the lifetime of the carrier decreases with increasing the light intensity. This decrease suggests that the photoconductivity mechanism in our samples was controlled by the transition trapping processes. The increase of Te content results in a monotonic decrease in the band gap and the free carrier life time of (As30Sb15Se55)100?xTex thin films. These results were interpreted on the basis of the chemical-bond approach. 相似文献
94.
A one pot synthesis of thienoazepinoisoindolones from the reaction of hydroxylactam‐alcohols, under acidic treatment, is described via an N‐acyliminium olefin cyclization. 相似文献
95.
96.
97.
Enolizable Carbonyls and N,O‐Acetals: A Rational Approach for Room‐Temperature Lewis Superacid‐Catalyzed Direct α‐Amidoalkylation of Ketones and Aldehydes 下载免费PDF全文
Bahria Touati Dr. Abderrahman El Bouakher Dr. Catherine Taillier Dr. Raja Ben Othman Prof. Dr. Malika Trabelsi‐Ayadi Dr. Sylvain Antoniotti Dr. Elisabet Duñach Prof. Dr. Vincent Dalla 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(17):6012-6022
An efficient catalytic room‐temperature direct α‐amidoalkylation of carbonyl donors, that is, ketones and aldehydes with unbiased N,O‐acetals, is described. Sn(NTf2)4 is an optimal catalyst to promote this challenging transformation at low loading and the reaction shows promising scope. A comprehensive and rational evaluation of this reaction has led to the establishment of an empirical scale of nucleophilic reactivity for a broad set of ketones that should be helpful in the synthetic design and development of carbonyl α‐functionalization methods. 相似文献
98.
Experimental investigation of frictional noise and surface-roughness characteristics 总被引:3,自引:0,他引:3
An experimental investigation into the nature of the noise generated when a stylus travels over a frictional surface has been
carried out using several engineering materials. The relation between the sound pressure level (SPL) and surface roughness
under various contact loads was established. An acoustic device was designed and constructed to be used as a reliable tool
for measuring roughness. For each tested material, it has been found that the filtered noise signal within a certain spectrum
bandwidth contains a specified frequency at which the amplitude is maximum. This frequency was named the dominating frequency
and was found to be a material constant independent of surface roughness and contact load. It was also found that the dominating
frequency for a given material is proportional to the sonic speed in that material. 相似文献
99.
Zayani Jaafar Othman Adel Matoussi Filippo Fabbri Francesca Rossi Giancarlo Salviati 《Applied Physics A: Materials Science & Processing》2014,116(3):1501-1509
This paper reports structural, optical and cathodoluminescence characterizations of sintered Zn1?x Mg x O composite materials. The effects of MgO composition on these film properties have been analyzed. X-ray diffraction (XRD) confirms that all composites are polycrystalline with prominent hexagonal wurtzite structure along two preferred orientations (002) and (101) for the crystallite growth. Above doping content x = 10 %, the formation of the hexagonal ZnMgO alloy phase and the segregation of the cubic MgO phase start. From reflectance and absorption measurements, we determined the band gap energy which tends to increase from 3.287 to 3.827 eV as the doping content increases. This widening of the optical band gap is explained by the Burstein–Moss effect which causes a significant increase of electron concentration (2.89 × 1018?5.19 × 1020 cm?3). The luminescent properties of the Zn1?x Mg x O pellets are studied by cathodoluminescence (CL) at room and liquid nitrogen temperatures under different electron beam excitations. At room temperature, the CL spectra of the Zn1?x Mg x O composites exhibit a dominant broad yellow-green light band at 2.38 eV and two ultraviolet emission peaks at 3.24 and 3.45 eV corresponding to the luminescence of the hexagonal ZnO and ZnMgO structures, respectively. For the doped ZnO samples, it reveals also new red peaks at 1.72 and 1.77 eV assigned to impurities’ emissions. However, the CL spectra recorded at 77 K show the presence of excitonic emission peaks related to recombination of free exciton (X A), neutral donor-bound excitons (D0X) and their phonon replicas. The CL intensity and energy position of the green, red and ultraviolet emission peaks are found to depend strongly on the MgO doping content. The CL intensity of the UV and red emissions is more enhanced than the green light when the MgO content increases. CL imaging analysis shows that the repartition of the emitting centers in Zn1?x Mg x O composites is intimately connected to the film composition and surface morphology. 相似文献
100.
A model has been formulated for the prediction of average saturation and the saturation profile through a fibrous bed during coalescence of secondary dispersion. The approach utilizes the Blake-Kozeny equation to relate experimental pressure drop data to saturation in the bed. Reasonable agreement was obtained between predicted saturations and those measured experimentally. The predicted saturation profiles could be used to determine other coalescer design parameters. 相似文献