Investigation of a resorcinol–formaldehyde resin by 13C-NMR spectroscopy and intrinsic viscosity measurement

Various molecular weight fractions and oligomers isolated from a novolac type resorcinol–formaldehyde (RF) wood adhesive resin were studied by ¹³C-NMR, gel permeation chromatography (GPC), and intrinsic viscosity measurements. The ¹³C-NMR results indicate that methylene groups occur mostly between C₄–C′₄ and C₂–C′₄ carbons and in minor amounts between C₂–C′₂ carbons of resorcinol rings. By suppressing the nuclear Overhauser effect (nOe) and using a long delay time for ¹³C-NMR measurements, reasonable methylene/aromatic carbon ratios were obtained from the aromatic C₁ carbon patterns that have resulted from different numbers of methylene groups bonded on the aromatic ring. This analysis results indicate that the RF resin has an appreciable amount of branch structures and compare favorably with the gel permeation chromatography and intrinsic viscosity measurement results. © 1993 John Wiley & Sons, Inc.