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21.
T. Philip Gnanarajan A. Sultan Nasar N. Padmanabha Iyer Ganga Radhakrishnan 《Journal of polymer science. Part A, Polymer chemistry》2000,38(22):4032-4037
A set of poly(urethane‐imide)s were prepared using blocked Polyurethane (PU) prepolymer and pyromellitic dianhydride (PMDA). The PU prepolymer was prepared by the reaction of polyether glycol and 2,4‐tolylene diisocyanate, and end capped with N‐methyl aniline. The PU prepolymer was reacted with PMDA until the evolution of carbon dioxide ceased. The effect of tertiary amine catalysts, organo tin catalysts, solvents, and reaction temperature were studied and compared with the poly(urethane‐imide) prepared using phenol‐blocked PU prepolymer. N‐methyl aniline blocked PU prepolymer gave a higher molecular weight poly(urethane‐imide) at a lower reaction temperature in a shorter time. Amine catalysts were found to be more efficient than organo tin catalysts. The reaction was favorable in particular with N‐ethylmorpholine and diazabicyclo(2.2.2)octane (DABCO) as catalysts, and dimethylpropylene urea as a reaction medium. The poly(urethane‐imide)s were characterized by FTIR, GPC, TGA, and DSC analyses. The molecular weight decreased with an increase in reaction temperature. The thermal stability of the PU was found to increase by the introduction of imide component. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4032–4037, 2000 相似文献
22.
23.
Pralay Maiti Ganga Radhakrishnan Palanisamy Aruna Goutam Ghosh 《Macromolecular Symposia》2006,241(1):51-59
Novel polyurethane gels have been reported in common solvent like dimethyl formamide (DMF). Polyurethanes have been synthesized from diisocyanates, diols and rigid chain extenders. We have illustrated the influence of chemical structure of the chain extenders on gelation rate, thermal property and morphology of the gels in DMF. Gelation rate increases significantly with the rigidity of the chain extender. Introduction of more rigid chain extender molecules in polyurethane prepolymer enhanced the thermal stability of the pure polymer. On the contrary, the solvent retention power of the gels gradually decreases with increasing rigidity of chain extender presumably because of the poor dispersion/greater aggregation of the hard segments in the soft segment matrix. Morphology and formation of gelation have been discussed. 相似文献
24.
Determination of hexavalent chromium by on-line dialysis ion chromatography in a matrix of strong colourants and trivalent chromium 总被引:3,自引:0,他引:3
Ganeshjeevan R Chandrasekar R Yuvaraj S Radhakrishnan G 《Journal of chromatography. A》2003,988(1):151-159
Hexavalent chromium detection in the presence of a high load of colourants without any false positive and in-procedure oxidation of Cr(III) is an important area of study. Colourants are a class of interfering substances in many spectroscopic analyses and chromatographic separations and detection. A purification method using an on-line dialysis technique for ion chromatography (IC) has been developed to remove water-soluble anionic dyes and particulate colourants and other substances to facilitate Cr(VI) quantification and the method is discussed. The dialysis was optimized with Cr(VI) standard solutions for quantification. The efficacy of the procedure for the removal of anionic dyes and detection of Cr(VI) was checked with a Cr(VI) spiked synthetic preparation containing a water-soluble dye and trivalent chromium. Soluble Cr(VI) extracted with organic dyes from environmental samples was analyzed. The method has a detection limit of 5 microg/l, recovery rate of 100% and analysis time less than 20 min. 相似文献
25.
Abstract The electron impact mass spectra of a series of substituted phenol blocked toluene diisocyanate crosslinkers were analyzed and a suitable dissociative pathway proposed. 相似文献
26.
The present communication aims at the study of the structural, dielectric, electrical and conduction properties of Bi3+/Yb3+ substituted BaTiO3 with a chemical composition of Ba0.5Bi0.5Yb0.5Ti0.5O3. The modified BaTiO3, could be synthesized by a solid state reaction technique. The X-ray diffraction data and pattern revealed the formation of the above compound with tetragonal crystal system. The material's molecular structure (Ba–Ti–O bond, O–Ti–O stretching-mode, metal-oxygen bond, optical band gap, and so on) was determined using room temperature Fourier transform infrared (FTIR) and UV–visible spectroscopic spectra. Detailed investigations of the material's electrical (dielectric/leakage current and impedance) behavior over a wide temperature (250C–5000C) and frequency (1 kHz–1000 kHz) range revealed the presence of capacitive, resistive, and conductive mechanisms. On the investigation of the polarization-electric field (P-E) hysteresis loop on multiple substitution, the change of ferroelectric polarization (spontaneous and residual) and storage density of BaTiO3 was observed. Defect chemistry of the modified barium compound has been discussed in the details. 相似文献
27.
Morao I Periyasamy G Hillier IH Joule JA 《Chemical communications (Cambridge, England)》2006,(33):3525-3527
Electronic structure calculations show that the cofactor H4B can be a key factor in a proton transfer relay in nitric oxide synthase, and that 4-amino-H4B cannot fulfill this role. 相似文献
28.
A. Varada Rajulu X.H. Li L. Ganga Devi G. Babu Rao Y.Z. Meng 《Cellulose (London, England)》2003,10(2):179-183
Ligno-cellulosic fabrics from the tree Hildegardia populifolia were coated with styrenated polyester resin, and their tensile strength, elastic modulus, and the percent elongation at break were determined. The effects of sodium hydroxide and a silane-coupling agent on the tensile properties of the fabric were also studied. It was observed that the tensile strength and the modulus decreased whereas the percent elongation at break increased with coating. The coupling agent improved the properties of the untreated and polyester-coated fabric, but a reverse trend was observed when the fabric was treated with sodium hydroxide. The possible reasons for this behavior are discussed. 相似文献
29.
Calix[4]arene derived bis(spirodienone) can act as a 4π component in cycloaddition reaction with a variety of carbo- and hetero-dienophiles yielding the bisadducts in excellent to quantitative yields. Bis(spirodienone) also undergoes addition reactions with dichlorocarbene resulting in mono- and bis-dichlorocyclopropyl derived bis(spiroenones) in excellent yields. 相似文献
30.
A. Sultan Nasar S. Subramani Ganga Radhakrishnan 《Journal of polymer science. Part A, Polymer chemistry》1999,37(12):1815-1821
N-Methylaniline-, diphenylamine-, and N-phenylnaphthylamine-blocked toluene diisocyanates (TDI) were prepared and characterized by IR, NMR spectroscopy, and nitrogen content analyses. The structure–property relationship of these adducts was established by reacting with hydroxyl-terminated polybutadiene (HTPB). The cure rate of the adduct increases from the N-phenylnaphthylamine- to diphenylamine- and to N-methylaniline-blocked TDI adduct. Simultaneous TGA/DTA results also confirm this trend, and the thermal stability of the adduct decreases in the following order: N-phenylnaphthylamine–TDI > diphenylamine–TDI > N-methylaniline–TDI. The gas chromatogram of the amine-blocked isocyanate confirms that the thermolysis products are the blocking agent and isocyanate. The solubilities of the adducts were carried out in polyether, polyester, and hydrocarbon polyols, and it was found that the N-methylaniline–TDI adduct shows higher solubility than the rest and also found that the polyester polyol shows higher solvating power against the adducts than the polyether and hydrocarbon polyols. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1815–1821, 1999 相似文献