Forest Products Laboratory

Title: Resorcinol-formaldehyde reactions in dilute solution observed by carbon-13 NMR spectroscopy

Author: Christiansen, Alfred W.

Date: 2000

Source: Journal of applied polymer science. Vol. 75 (2000).:p. 1760-1768 : ill.

Description: A recently discovered coupling agent, hydroxymethylated resorcinol (HMR), based on resorcinol-formaldehyde, can greatly enhance wood-to-epoxy resin bond durability in exterior applications. However, for HMR to be most effective, it needs to be prepared a few hours before it is applied to the wood surface. In this study, carbon-13 nuclear magnetic resonance (NMR) spectroscopy was used to monitor composition of HMR as a function of time to characterize which chemical groups are present in solution when HMR is applied. A quantitative assessment of formaldehyde-derived groups required the use of 99% 13C-enriched formaldehyde. Hydroxymethyl groups, primarily attached to the 4-position of resorcinol, and hemiformal groups formed very quickly. Signals from methylene linkages between resorcinol rings began to appear 20 min into the reaction. Formaldehyde was consumed quickly; 95% was bound to resorcinol rings within 1.7 h. By 3 h, 16% had been converted to methylene linkages, and by 8.3 h, 40% was converted. Another set of NMR experiments was used to monitor the dependency of peak positions of resorcinol solution as a function of pH. These experiments showed significant effects, especially between pH 7.7 and 9.1, which explains chemical shift changes observed during the HMR reaction.

Keywords: Resins, Adhesives, Resorcinol, Formaldehyde, Chemical reactions, Nuclear magnetic resonance spectroscopy, Carbon, Solutions, Hydroxymethylated resorcinol, Coupling agents

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Citation

Christiansen, Alfred W.  2000.  Resorcinol-formaldehyde reactions in dilute solution observed by carbon-13 NMR spectroscopy .   Journal of applied polymer science. Vol. 75 (2000).:p. 1760-1768 : ill..