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Polymers 2016, 8(11), 391;

A 13C-NMR Study on the 1,3-Dimethylolurea-Phenol Co-Condensation Reaction: A Model for Amino-Phenolic Co-Condensed Resin Synthesis

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
Authors to whom correspondence should be addressed.
Academic Editor: Antonio Pizzi
Received: 13 September 2016 / Revised: 31 October 2016 / Accepted: 1 November 2016 / Published: 8 November 2016
(This article belongs to the Special Issue Renewable Polymeric Adhesives)
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The reactions of di-hydroxymethylurea with phenol under alkaline (pH = 10), weak (pH = 6) and strong acidic (pH = 2) conditions were investigated via the 13C-NMR method. Based on the proposed reaction mechanisms, the variations of the structures of different condensed products were analyzed and the competitive relationship between self- and co-condensation reactions was elucidated. The required experimental conditions for co-condensations were clearly pointed out. The main conclusions include: (1) the self-condensation between urea formaldehyde (UF) or phenol formaldehyde (PF) monomers were dominant while the co-condensations were very limited under alkaline conditions. This is because the intermediates produced from urea, methylolurea and phenol are less reactive in co-condensations with respect to self-condensations; (2) under weak acidic conditions, the self-condensations occurred exclusively among the UF monomers. The co-condensation structures were not observed; and (3) the co-condensations became much more competitive under strong acidic conditions as the relative content of the co-condensed methylenic carbon accounts for 53.3%. This result can be rationalized by the high reactivity of the methylolphenol carbocation intermediate toward urea and methylolurea. The revealed reaction selectivity and mechanisms may also be applied to the synthesis of those more complex co-condensed adhesives based on natural phenolic and amino compounds. View Full-Text
Keywords: co-condensed resin; phenol-urea-formaldehyde; 13C-NMR; mechanism co-condensed resin; phenol-urea-formaldehyde; 13C-NMR; mechanism

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Cao, M.; Li, T.; Liang, J.; Wu, Z.; Zhou, X.; Du, G. A 13C-NMR Study on the 1,3-Dimethylolurea-Phenol Co-Condensation Reaction: A Model for Amino-Phenolic Co-Condensed Resin Synthesis. Polymers 2016, 8, 391.

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