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121.
122.
Joseph P. Sattler George J. Simonis 《International Journal of Infrared and Millimeter Waves》1984,5(4):465-473
We report the refractive indices and absorption coefficients for four beryllia (BeO) ceramic samples. These dielectric properties have been measured over the range from 4 to 18 cm–1 by use of a Michelson interferometer. The index n, follows the linear relationship n=0.6517 cm3/g×+0.7130 with density, , over the range 2.8<<3.0 g/cm3. 相似文献
123.
Influence of isotacticity and molecular weight on the properties of metallocenic isotactic polypropylene 总被引:1,自引:0,他引:1
The relationships between structure and properties have been established for isotactic polypropylene, iPP, homopolymers synthesized by metallocene catalyst systems. These iPPs exhibit different isotacticity degrees and molecular weights, and several thermal treatments during their processing have been applied. The most important factor affecting the structure and properties of these polymers is the isotacticity content. The thermal treatment, i.e., the rate of cooling from the melt, is also important and a clear molecular weight effect has been also found for the sample with lowest Mw. These factors affect the thermal properties, the degree of crystallinity and, therefore, the structural parameters and the viscoelastic behavior. A slow cooling from melt favors the formation of the γ phase instead of the α modification. The storage modulus, Young modulus and microhardness values increase as crystallinity does, independently of the origin of this increase: higher isotacticity or application of a slow crystallization from the melt. 相似文献
124.
125.
《Surface and interface analysis : SIA》2003,35(3):282-286
We have developed a high‐speed image processing CCD video camera for real‐time energy‐loss imaging using a conventional electron microscope with an energy‐loss imaging facility. As an initial demonstration of real‐time lock‐in energy‐loss imaging, a background‐subtracted energy‐loss image was observed by attaching the high‐speed image processing CCD video camera to an analytical electron microscope equipped with a floating‐type energy‐loss imaging analyser. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
126.
Helena?H?kanssonEmail author Per?Ahlgren Ulf?Germg?rd 《Cellulose (London, England)》2005,12(3):327-335
The amount of disordered material in two types of hardwood kraft pulps was estimated by determining the weight loss at the
point where the levelling-off degree of polymerisation (LODP) was reached. The pulps used were commercial pulps viz (1)one
conventional birch kraft and (2)one mixed hardwood (MHW) kraft pulp that had been prehydrolysed prior to cooking. The results
indicated that the hemicellulose xylan is closely associated with the cellulose in commercial birch pulps. It is therefore
only possible to use LODP as a measure of the crystallite length of hardwood cellulose in highly purified pulps, such as prehydrolysed
kraft pulp. A model explaining the LODP-results is proposed. 相似文献
127.
Summary Herein is reported an analytical solution to the peak broadening or peak dispersion/flattening equation based on the recently proposed Instrumental Spreading Shape Function and its application to correction for imperfect resolution (inadequate peak separation and/or excessive peak broadening) for higher molecular weight averages. The relationship of these higher MW averages with the familiar Weight Average and number average molecular weights is also discussed. Criteria for perfect resolution are specified and a true molecular weight calibration curve is accordingly defined. 相似文献
128.
Electron impact and methane chemical ionization mass spectra were obtained following gas chromatography/mass spectrometry for several gem-difluoropropargyl compounds, which had been synthesized as potential intermediates for synthesis of gem-difluoromethylene-containing C-3 acetylenes. EI spectra were variable with respect to the presentation of molecular ions, depending on substituent functional groups present. Methane-CI spectra were characterized by loss of 19 mass units from molecular weight with all compounds examined. These [M − 19]+ ions often presented as base peaks of the CI spectra, and were more reliably present and abundant than [M + 1]+ ions for these compounds. These ions could have been formed by elimination of HF from the protonated molecules under conditions of methane chemical ionization. 相似文献
129.
We report a thermal analysis study of the effect of molecular weight on the amorphous phase structure of poly(phenylene sulfide), PPS, crystallized at temperatures just above the glass transition temperature. Thermal properties of Fortron PPS, having viscosity average molecular weights of 30000 to 91000, were characterized using temperature modulated differential scanning calorimetry (MDSC). We find that while crystallinity varies little with molecular weight, the heat capacity increment at the glass transition decreases as molecular weight decreases. This leads to a smaller liquid-like amorphous phase, and a larger rigid amorphous fraction, in the lower molecular weight PPS. For all molecular weights, constrained fraction decreases as the scan rate decreases.This research is supported by the U. S. Army Research Office through contract DAAH04-96-1-0009. The authors thank Hoechst Celanese for providing different molecular weight Fortron samples and Dr. George Collins for providing sample information. The authors acknowledge the assistance of Elizabeth Oyebode and Leonardo Grimaldi with sample preparation and MDSC work. 相似文献
130.
Elena Khomko Leonid Mashlyakovskiy Claudio Tonelli 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5354-5371
The effect of catalyst dibutyltin dilaurate (DBTDL) on the kinetics of urethane formation reactions of α,ω‐bis(hydroxy)‐terminated fluoropolyethers Fomblin® Z‐DOL TXs (FPEs) of various molecular weights and poly(oxyethylene) glycol PEG‐400 with isophorone diisocyanate (IPDI) in hexafluoroxylene (HFX) and tetrahydrofuran (THF) at 40 °C and NCO:OH = 2:1 have been studied in a broad range of catalyst (0.10–9.00) ×10?4 M and total reagents (10.0–60.1 wt %) concentrations. The rate of tin‐catalyzed second‐order reactions (with respect to diol and diisocyanate) was found to be proportional to the square root of catalyst concentration [DBTDL]0.5 both in low polar (HFX) and polar (THF) solvents. Effect of catalyst saturation was revealed for all the reaction systems at higher DBTDL concentrations as well as the appearance of the limiting catalyst concentrations Clim below which the rates of reaction were close to zero. Based on these findings new effective rate coefficients have been derived k = kcat/(C ? C) that are independent of the total reagent concentration in the range of 10.0–60.1 wt % ([OH] = 0.10–0.91 equiv/L). This new approach highlights that the rate of the tin‐catalyzed urethane formation reactions of α,ω‐bis(hydroxy)‐terminated fluoropolyethers Z‐DOL TXs with IPDI in HFX at 40 °C and NCO:OH = 2:1 increases significantly with increasing MW of FPE from 776 up to 3405. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5354–5371, 2004 相似文献