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

Abstract Various molecular weight fractions and oligomers isolated from a novolac type resorcinol–formaldehyde (RF) wood adhesive resin were studied by 13 C‐NMR, gel permeation chromatography (GPC), and intrinsic viscosity measurements. The 13 C‐NMR results indicate that methylene groups occur mostly between C 4 –C′ 4 and C 2 –C′ 4 carbons and in minor amounts between C 2 –C′ 2 carbons of resorcinol rings. By suppressing the nuclear Overhauser effect (nOe) and using a long delay time for 13 C‐NMR measurements, reasonable methylene/aromatic carbon ratios were obtained from the aromatic C 1 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.