NMR AND INTRINSIC-VISCOSITY STUDY OF 2 DIFFERENT PHENOL-FORMALDEHYDE RESOL RESINS

Two different phenol-formaldehyde (PF) resol resins used as binders in wood products manufacture were subjected to acetylation and fractionation, and the fractions were studied by quantitative NMR, intrinsic viscosity, and number average molecular weight measurements. The NMR results described the structures of these resin fractions reasonably well as polymeric methylene (hydroxymethyl)-phenols. However, the solution C-13 NMR results, obtained with long delay times and nuclear Overhauser effect (NOE) suppression, showed significant deviations from the structure, apparently due to the limitations of the method used. While higher molecular weight fractions deviated more than low molecular weight fractions, resin A fractions deviated less than resin B fractions, reflecting the structural differences between the two resins. Mark-Houwink correlation results for resin A fractions indicated nonuniform structures, and for resin B fractions the correlation resulted in an "a" value of 0.21 in chloroform and 0.12 in benzene, indicating a compact structure typical of branched polymers. Intrinsic viscosities of resin A fractions expanded less than those of resin B fractions upon a solvent change from benzene to chloroform. Resin B fractions showed higher, more variable Huggins' constants than those of resin A fractions, indicating their higher tendency of molecular associations in solution, which was interpreted to give rise to their higher deviations in solution C-13 NMR results.