Infra-red Study of Structural Changes during the Pyrolysis of a Phenol-formaldehyde Resin

On pyrolysis of a phenol-formaldehyde resin at temperatures up to 700°C there was no change in the infra-red spectrum below 300°C but above this temperature the hydroxyl absorption began to decrease. This and other changes indicated the formation of diphenyl ether type linkages between benxene nuclei with the elimination of water. Above 400°C the changes which occurred in the spectra suggested that dibenzyl ether structures decompose to benzylphenyl ethers and that xanthene or diphenylene oxide type oxygen groups are probably formed. Some methylcne bridges dtcompose, forming carbonyl or methyl groups, which reach a maximum content at SOO-550°C Above 5oO”C rhe diphenyl ether type linkages decompose rapidly and poly-substitution of benzene nuclei increases. From 6OO“C onwards the aromatic hydrogen also begins to be eliminated and the spectra become structureless, perhaps because of the condensation of aromatic nuclei. The oxygen left at this stage may be present as inner-ring oxygen, as in diphenylene oxide.