NMR Analysis to Identify Biuret Groups in Common Polyureas
- 24 Downloads
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 °C. 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 °C. In addition, this NMR analysis was also applied to a PU obtained by copolymerization of TDI with ethylene diamine (EDA) and water at 65 °C 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.
KeywordsDiisocyanate Polyurea Chemical structure Biuret NMR spectroscopy
Unable to display preview. Download preview PDF.
This work was financially supported by the National Natural Science Foundation of China (Nos. 21274054, 21304038 and 51473066), Research Foundation of University of Jinan (No. XKY1604) and by Science & Technology Development Plan of Shandong Province (No. 2017GGX202009), China.
- 14.Sumi, M.; Chokki, Y.; Nakai, Y.; Nakabayashi, M.; Kanzawa, T. Studies on the structure of polyurethane elastomers. I. NMR spectra of the model compounds and some linear polyurethanes. Die Makromol. Chem. 1964, 78(1), 146–156.Google Scholar
- 18.Okuto, H. Studies on the structure of polyurethane elastomers. II. High resolution NMR spectroscopic determination of allophanate and biuret linkages in the cured polyurethane elastomer: Degradation by amine. Die Makromol. Chem. 1966, 98(1), 148–163.Google Scholar
- 20.Zhang, X.; Zhang, X. Y.; He, Y.; Chen, H. Progress in synthesis and characterization of HDI biuret. Pain Coat. Ind. 2011, 41(10), 71–75.Google Scholar
- 27.Li, S.; Zhu, X.; Kong, X. Z.; Jiang, X. One step synthesis of porous polyurea by using TDI and EDA and its characterization. Acta Polymerica Sinica (in Chinese) 2016, (3), 391–398.Google Scholar
- 29.Alam, T. M.; Jenkins, J. E. “Advanced Aspects of Spectroscopy”, Intech, Croatia, 2012, p. 279–301.Google Scholar
- 31.Harris, R. F.; Kinney, J. E.; Savina, M. R.; Jeor, V. L. S.; Bicerano, J.; Durvasula, V. R.; Moreno, L. N. Synthesis and characterization of urea-based polyureas: 1. Urea-terminated poly(1,6-hexamethyleneurea) polyol dispersions. Polymer 1995, 36(22), 4275–4285.Google Scholar