Structure of phenol-formaldehyde polycondensates

Abstract

Prepolymer resol resins with the molar ratio of phenol/formaldehyde 1/ 2.4 and different amounts of NaOH were synthesized and characterized using 13C NMR spectra for samples in CD3OD solution. Nearly the full substitution in ortho and para aromatic positions occurred, and quite constant ratios of hydroxymethyl/methylene or o,p'/p,p'-methylene groups were obtained. The content of free formaldehyde strongly depends on the NaOH content in synthesis. The prepolymeric chains end mainly with aromatic rings substituted with two ortho-hydroxymethyl groups. The alkali-dependent content of phenoxide ions causes the downfield shifts of 13C signals for ortho-hydroxymethyl groups from 62.8 ppm to 64.4 ppm and for aromatic carbon bearing the hydroxyl group from 157 ppm to 163 ppm. A comparison with industrial resol resin for the manufacture of plywood is presented.