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Polymers 2017, 9(3), 109;

The Influence of pH on the Melamine-Dimethylurea-Formaldehyde Co-Condensations: A Quantitative 13C-NMR Study

1,3,* , 1
The Yunnan Province Key Lab of Wood Adhesives and Glued Products, Southwest Forestry University, Kunming 650224, China
College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037, China
The Key Laboratory of Forest Resources Conservation and Use in the Southwest Mountains of China, Southwest Forestry University, Ministry of Education, Kunming 650224, China
Authors to whom correspondence should be addressed.
Academic Editor: Antonio Pizzi
Received: 22 February 2017 / Revised: 13 March 2017 / Accepted: 15 March 2017 / Published: 17 March 2017
(This article belongs to the Collection Polymeric Adhesives)
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1,3-dimethylurea (DMU) was used to mimic urea and to model melamine-urea-formaldehyde (MUF) co-condensation reactions. The products of 1,3-dimethylurea-formaldehyde (DMUF), melamine-formaldehyde (MF), and melamine-1,3-dimethylurea-formaldehyde (MDMUF) reactions under alkaline and weak acidic conditions were compared by performing quantitative carbon-13 nuclear magnetic resonance (13C-NMR) analysis. The effect of pH on the co-condensation reactions was clarified. With the presence of the methyl groups in DMU, the appearance or absence of the featured signal at 54–55 ppm can be used to identify the co-condensed methylene linkage –N(–CH3) –CH2–NH–. Under alkaline condition, MDMUF reactions produced primarily MF polymers and the featured signal at 54–55 ppm was absent. Even though the co-condensations concurrently occurred, undistinguishable and very minor condensed structures with ether linkage were formed. Differently, under weak acidic condition, the relative content of co-condensed methylene carbons accounts for over 40%, indicating the MDMUF co-condensation reactions were much more competitive than the self-condensations. The formation of reactive carbocation intermediate was proposed to rationalize the results. View Full-Text
Keywords: co-condensation; melamine-dimethylurea-formaldehyde; 13C-NMR co-condensation; melamine-dimethylurea-formaldehyde; 13C-NMR

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Cao, M.; Li, T.; Liang, J.; Du, G. The Influence of pH on the Melamine-Dimethylurea-Formaldehyde Co-Condensations: A Quantitative 13C-NMR Study. Polymers 2017, 9, 109.

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