Structural analysis of phenolic resole resins

Abstract

Abstract The chemical structure and cure characteristics of a group of phenolic resole resins were studied by means of three major analytical techniques. In particular, the effects on structure and reactivity of formaldehyde/phenol ratio and the type of reaction catalyst used were studied. Gel permeation chromatography was used to determine resin molecular weight distributions, and NMR, to determine chemical structural features. In this connection a selective oxidation procedure, converting free methylol groups to adehydes, has allowed unambiguous determination of methylene ether bridge structures to be made from the NMR data. The F / P ratio in a resole largely determines the type of molecular structures which are formed. However, triethylamine as a catalysts tends to favor methylene ether bridge formation, whereas sodium hydroxide favors methylene bridges. The rate and direction of subsequent thermal cure of the resoles prepared is shown by differential scanning calorimetry to depend markedly on the type of catalyst present during the curing stage. The DSC curing curves are interpreted in the light of the structural information provided by NMR.