¹³C‐NMR analysis of formaldehyde resins

Abstract

I 3C-NMR spectroscopy has been applied to the analysis of formaldehyde containing resins. Samples have been prepared from phenols, urea and melamine with formaldehyde. The chemical shifts of the carbon atoms in the resins were measured relative to TMS. All the samples could be dissolved in DMSO-d6 which facilitated the comparison of signals in different resins.The spectra were interpreted with the aid of spectra of reference compounds and simple calculations based on additivity increments. Each type of resin gives a specific 13C-NMR spectrum in which lines can be assigned that give information on the structure of the resin in relation to the type of condensation or catalyst used. Moreover, the different ways in which formaldehyde is incorporated in the resins as methylene carbon can be unambiguously determined from the region between 20 and 100 ppm.This work shows that 13C-NMR spectroscopy is a powerful ,tool for the analysis of formaldehyde containing resins. ZUSAMMENFASSUNG:Die 3C-NMR-Spektroskopie wurde zur Analyse von Formaldehyd-Harzen verwendet. Aus Phenolen, Harnstoff und Melamin wurden mit Formalin Harze hergestellt. Die chemischen Verschiebungen dieser Harze wurden relativ zu TMS gemessen. Alle Harze waren in DMSO-d6 loslich, so da13 die Signale von unterschiedlichen Harzen verglichen werden konnten.Die Spektren wurden mit Hilfe der Spektren von Referenzsubstanzen und einfachen, auf Additivitat basierenden Rechenregeln interpretiert. Jeder Harztyp hat sein eigenes spezifisches Spektrum und enthalt Signale, die iiber die Struktur im Zusammenhang mit dem Katalysatortyp und der Kondensationsweise Auskunft erteilen. Die unterschiedlichen Formen, in denen Formaldehyd in diese Harze als Methylenkohlenstoff eingebaut ist, lassen sich unzweideutig aus dem Gebiet von 20 bis 100 ppm bestimmen.Diese Arbeit zeigt, daB sich die 13C-NMR Spektroskopie sehr gut fur die Analyse von Formaldehydharzen eignet.

Effect of alkalinity on the structure of phenol–formaldehyde resol resins

“…The mechanism and kinetics of the alkali-catalyzed reaction of phenol with formaldehyde, the physical properties of resins under alkaline conditions, and the effects of the curing alkalinity on resins have been widely researched. [1][2][3][4][5][6][7][8][9][10][11] In this study, the effects of the methylation alkalinity (first-stage alkalinity after an initial addition of a NaOH catalyst) and the condensation alkalinity (second-stage alkalinity after subsequent addition of a NaOH catalyst) on the chemical structures and reactivity in two phenol-formaldehyde resin series were studied by 13 C-NMR spectroscopy and differential scanning calorimetry (DSC).…”

Hyperbranched phenol-formaldehyde resins

“…*^^"***V^' I^N /* ""Nl AW While intensities of o-p' and p-p' methylene signals (8=36 ppm and 8= 40.9 ppm, respectively [21] are comparable with each other in the case of conventional novolak (Fig.4a), methylene o-p' signal predominates significantly for the second generation products (Fig.4c). Methylene o-o' signal (8=31.4 ppm) remains weak throughout the novolaks investigated.…”

“…It is clearly shown in the Fig.4 that intensity of the signal at 6= 36 ppm which corresponds to carbon atoms of o-p'methylene linkages [21], is growing from the conventional novolak towards higher generation of hyperbranched ones.…”

Examination of selected synthesis parameters for typical wood adhesive-type urea-formaldehyde resins by13C NMR spectroscopy. I

“…Most of the methylene-ethers are formed in the initial alkaline condensation step, [15][16][17][18][19][20] as indicated by their relatively high concentrations in Samples 1AU/1BU. Type I methylene-ethers, normally the highest among methylene-ethers, started out in Samples 1AU/1BU at a relatively high level and decreased slowly as the polymerization reaction progressed with a rate slightly faster at the higher reaction temperature used.…”

“…[15][16][17][18][19][20] However, the low-field 13 C NMR methods used in the past gave somewhat poor peak resolutions and sensitivity with the quantitative data obtainable being limited in accuracy.…”