Influence of the amount of catalyst and initial pH on the phenolic resol resin formation

The influence of the added amount of triethylamine as phenolic resol resin catalyst and that of the initial pH were studied for resols synthesized at 80 degrees C with F/P = 1.8. The evolution of phenol and first formed addition products were quantitatively followed by highperformance liquid chromatography (HPLC) and final prepolymers were analyzed by C-13 NMR spectroscopy. The catalyst amount kinetically and mechanistically affected the prepolymer formation. The higher the amount of added catalyst the higher reactant consumption rates and product formation rates. The ortho directing characteristics of triethylamine for the addition of formaldehyde onto phenolic sites were observed. It could be stated that two mechanisms for the addition of formaldehyde occurred simultaneously. On the one hand, hydroxyl groups favoured the formation of phenolate ions, which would favour addition onto pam phenolic positions. On the other hand, formaldehyde, phenol, and triethylamine could be involved in the formation of an intermediate transition state, favouring addition onto ortho sites, due to the ortho directing properties of triethylamine. The influence of the studied pH range did not give rise to significant differences on the resol resin prepolymer formation. (C) 2000 Elsevier Science Ltd. All rights reserved.