A look at the development of the phenolic OH groups (Fig. ) shows that increased absorption values are already measured without additional reagents, but these do not follow a time course. For the test series with SPC, an increase can be perceived, which increases with advancing time, but abruptly decreases after 60 min. This correlates with an abrupt increase in carbonyl functions. The assumption is that here also a part of the phenolic OH groups is oxidised by reactive species. For the combined series of SPC/NaOH no temporal change can be observed. Due to the comparatively high temperatures and the strongly oxidising environment, the release of OH groups and their subsequent oxidation probably compete with various condensation reactions. The highest absorption values for basic degradation with NaOH are already reached after 5 minutes. This observation is in good agreement with increased absorption values in the range of 3500-3000 cm -1 which is characteristic for all OH groups. The hypothesis is supported by a decrease of the characteristic ether vibrations, which speaks for their cleavage and additionally explains the increase of OH groups. As the reaction time progresses, condensation processes occur, which causes the absorption of the OH groups to decrease and the vibrations for ether and ester to increase continuously after 15 minutes.