Oxidative degradation of phenol–formaldehyde polycondensation initial degradation reactions

The initial degradation of phenol–formaldehyde polycondensates has been found to follow two distinct pathways. Oxidation of the dihydroxydiphenylmethane unit to substituted dihydroxybenzophenone and dihydroxybenzhydrol species has been observed and substantiated using model compounds to support the characteristic infrared spectral changes. The ingrowth of ketonic species has been evaluated kinetically on phenol–formaldehyde polymers which have been cured fully to remove residual methylol groups. The rate constants have been found to be a factor of 33 times slower than those observed earlier for partially cured resins having relatively large numbers of residual methylol groups present. The activation energy for the initial ketonic carbonyl was found to be 15.6 ± 3.9 kcal. This value compares favorably with other values obtained for phenolic oxidation. The potential oxidation of methylol groups to substituted salicylic acid moieties could not be substantiated spectrally. However, a polymer containing 2‐methylol‐ p ‐cresol on oxidation gave a small quantity of 5‐methylsalicylic acid, thus substantiating methylol oxidation in competition with the further curing reaction which produces new diphenylmethane linkages. The secondary oxidation resulting in chain scission can be separated on a time scale from oxidations of the methylol type. The present study therefore significantly extends the initial oxidative degradation chemistry of phenol–formaldehyde polycondensates.