We used 13 C and 1 H NMR spectroscopy to examine the equilibrium speciation in formaldehyde−methanol− water solutions at moderate formaldehyde concentrations such as those used in the synthesis of formaldehyde-based organic gels. Concentrations of small methylene glycol oligomers and their methoxylated forms found in these solutions were quantitatively determined over a range of formaldehyde concentrations and methanol−water ratios, and at temperatures between 10 and 55 °C. Using the measured concentrations, equilibrium constants for methylene glycol dimer and trimer formation as well as methoxylation of these oligomers were calculated. Based on this, we developed a quantitative equilibrium model for calculation of formaldehyde-related species concentrations over a range compositions relevant for formaldehyde based sol−gel processes allowing for more rational design of formaldehyde polymerization systems.

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Resorcinol and formaldehyde reactions were quantitatively monitored by means of 1 H and 13 C NMR spectroscopy at room temperature (293K) before heat treatment leading to formation of organic gels. We found that resorcinol substitution with formaldehyde starts with an initial surprisingly rapid step followed by a more gradual depletion of the reactants. Substituted species with both monomeric and dimeric hydroxymethyl groups were observed immediately after mixing of the reagents with the proportion of formaldehyde-based solution species consumed between 30 and 50%. Substituted resorcinol species can be all accounted for by solution-phase NMR at ambient conditions before they form nanoscale clusters upon heating. It can therefore be expected that the final properties of resorcinol-formaldehyde gels depend not only on the composition of reaction mixtures and duration of the high temperature treatment but also on the manner and period of reagent mixing (a hitherto overlooked synthesis step), as different amounts of alternatively substituted resorcinol can be produced before heat treatment commences.