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NMR Analysis to Identify biuret Groups in Common Polyureas

Chinese Journal of Polymer Science 2018年第10期36卷 1150-1156页

作者： Wei-Guang Qiu Fei-Long Zhang Xu-Bao Jiang Xiang-Zheng Kong College of Chemistry and Chemical Engineering University of Jinan

Polyureas （PU） are well known as a class of high impact engineering materials, and widely used also in emerging advanced applications. As a general observation, most of them are only soluble in a very limited number of highly protonic solvents, which makes their chemical structure analysis a great challenge. Besides the presence of abundant hydrogen bonding, the poor solubility of PU in common organic solvents is often ascribed to the formation of biuret crosslinking in their molecular chains. To clarify the presence of biuret groups in PU has been of great interest. To this end, two samples, based on hexamethylene diisocyanate （HDI） and toluene diisocyanate （TDI） respectively, were synthesized by precipitation polymerization of each of these diisocyanates in water-acetone at 30℃. Their chemical structures were analyzed by high resolution magic angle spinning （HR-MAS） NMR, and through comparison of their NMR spectra with those of specially prepared biuret-containing polyurea oligomers, it was concluded that biuret group was absent in all the PU prepared at 30 ℃. In addition, this NMR analysis was also applied to a PU obtained by copolymerization of TDI with ethylene diamine （EDA） and water at 65 ℃ in EDA aqueous solution. It was confirmed that biuret unit was also absent in this PU and that EDA was more active than water towards TDI. The presence of EDA was crucial to the formation of uniform PU microspheres. This study provides therefore a reliable method for the analysis of PU chemical structure.

关键词： Diisocyanate Polyurea Chemical structure biuret NMR spectroscopy

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Study of Dehydrocoupling Reactions of Diorganotin Dihydrides R^1R^2SnH2 with biuret

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Chinese Journal of Chemistry 2007年第7期25卷 1036-1040页

作者： DEEP, Gagan NARULA, A.K. School of Basic and Applied Sciences Guru Gobind Singh Indraprastha University Kashmere Gate Delhi 110006India

The reaction of unsymmetrical phenylmethyltin dihydride （PhMeSnH2）, phenylethyltin dihydride （PhEtSnH2）, phenylbutyltin dihydride （PhBuSnH2） and butylmethyltin dihydride （BuMeSnH2） with biuret （HAL） proceeds via SnH/NH dehydrocoupling to afford the corresponding tetra-coordinate cyclic products. The reactions in the molar ratios of 1 ： 1, 2 ： 1 and 1 ： 2 have been studied. The yellow derivatives so isolated were soluble in polar solvents and insoluble in nonpolar solvents. It was found that 1 ： 1 reaction went to completion while 2 ： 1 and 1 ： 2 did not go to completion. The derivatives had been characterized by elemental analysis and spectroscopic techniques viz. IR, ^1H NMR, ^13C NMR, ^119Sn NMR. DSC and TGA of the reaction products have also been studied. All the derivatives were thermally stable upto （1904- 10）℃ and degradation occurred after that.

关键词： butylnmethylti dihydride biuret synthesis spectroscopic analysis thermal behaviour

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Alleviation Effect of Trace Elements Application on biuret Phytotoxicity of Maize

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Agricultural Science & Technology 2016年第3期17卷 599-602页

作者：贾亮郭宗端王州贾洪秀李新柱刘毅金正大生态工程集团股份有限公司复合肥料国家地方联合工程研究中心农业部植物营养与新型肥料创制重点实验室山东临沭276700

A pot experiment was carried out to study the effect of trace elements on the biuret toxicity of maize, with the aim to provide theoretical basis for improving the urea-based compound fertilizer production and reducing the biuret toxicity. The results showed that the compound fertilizer with 2% and 4% biuret caused obvious toxicity on the maize. The plant became short, and the biomass decreased, and the toxicity phenomenon of maize would become more obvious when the biuret leve increased. Application of 5% EDTA-Zn and 0.4% B could reduce the toxicity of bi uret in fertilizers. The toxicity would be eliminated completely when the level of biuret was 2% in compound fertilizers, while the toxicity effects of 4% biuret was just alleviated to a certain extent. In addition, application of 2% amino acids with ureabased compound fertilizer could promote root absorption of biuret, and increase the biuret toxicity. In conclusion, the urea compound fertilizers with high biuret concentrations should be applied with appropriate trace elements to reduce the biuret dam age. It was suggested that the biuret content in the complex fertilizers for maize should be controlled below 2%, and appropriate trace elements should be applied at the same time.

关键词： Trace elements Maize biuret Phytotoxicity

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Deactivation of Cu-SAPO-34 by urea-related deposits at low temperatures and the regeneration

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Journal of Environmental Sciences 2019年第7期31卷 43-51页

作者： Yue Ma Xiaodong Wu Junyu Zhang Rui Ran Zhichun Si Duan Weng The Key Laboratory of Advanced Materials of Ministry of Education School of Materials Science and Engineering Tsinghua University School of Environment Tsinghua University Graduate School at Shenzhen Tsinghua University

Selective catalytic reduction(SCR) with urea catalyzed by Cu-SAPO-34 is an effective method to eliminate NO_x from diesel exhaust. However, urea-related deposits may form during cold-start and urban driving due to low exhaust temperatures. The activity of CuSAPO-34 at 175°C is significantly degraded by urea exposure, and 300°C is required for regeneration. Through in-situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) and temperature-programmed hydrolysis studies, the dominant stable deposit at 175°C is identified as biuret, which can be eliminated at 300°C. The urea-derived deactivation and regeneration mechanisms of Cu-SAPO-34 were compared with those of anatase-supported catalysts.

关键词： SCR Urea biuret Cu-SAPO-34 Deactivation

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