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

被引:11
作者
Cao, Ming [1 ,2 ]
Li, Taohong [1 ]
Liang, Jiankun [1 ]
Wu, Zhigang [1 ]
Zhou, Xiaojian [1 ]
Du, Guanben [1 ,2 ]
机构
[1] Southwest Forestry Univ, Yunnan Prov Key Lab Wood Adhes & Glued Prod, Kunming 650224, Peoples R China
[2] Nanjing Forestry Univ, Coll Mat Sci & Engn, Nanjing 210037, Jiangsu, Peoples R China
基金
“十二五”国家科技支撑计划重点项目”; 中国国家自然科学基金;
关键词
co-condensed resin; phenol-urea-formaldehyde; C-13-NMR; mechanism; UREA-FORMALDEHYDE RESINS; CATALYZED SELF-CONDENSATION; COCONDENSED RESINS; HARDENING ACCELERATION; SYNTHESIS PARAMETERS; FAST ADVANCEMENT; CURING BEHAVIOR; KINETICS; MECHANISMS; ADHESIVES;
D O I
10.3390/polym8110391
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
The reactions of di-hydroxymethylurea with phenol under alkaline (pH = 10), weak (pH = 6) and strong acidic (pH = 2) conditions were investigated via the C-13-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.
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页数:15
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