ANALYSIS OF THE FORMATION AND CURING REACTIONS OF RESOLE PHENOLICS

The chemical composition and molecular size distributions of a series of soluble resole phenolics was studied by high resolution 13C NMR, IR, GPC, and viscosity techniques. The curing reactions were then followed by IR and solid state 13C NMR techniques. The ultimate degree of cure increases with curing time and temperature. The molecular weight of the precursor resole can be increased with increasing formaldehyde/phenol mole ratio and increased condensation reaction time and temperature. The degree of cure achieved under given conditions is directly proportional to the molecular weight of the precursor resole. The condensation catalyst has a great effect on resole composition and molecular size. It also influences preferential methylolation at the para position to the phenolic OH group in the following increasing order Ba(OH)2, NaOH, Na2CO3. The curing pH affects the degree of cure as well as the type of linkages formed. Methylene bridges are almost exclusive at high or very low pH's, while dibenzyl ether bridges predominate at neutral pH. High resolution 13C NMR spectroscopy is the most powerful tool to study soluble resoles. Infrared spectroscopy supplies qualitative results. Solid state 13C NMR is useful to study polymers during the curing process but there are inherent limitations and potential errors in this method. Copyright © 1990 John Wiley & Sons, Inc.