The low wavenumber range from 1100 cm -1 consists of combination vibration bands of different deformation and framework vibrations and is accordingly more difficult to interpret. While the spectral range around 1300-1100 cm -1 is characteristic for aryl-aryl ethers and a clear degradation takes place here, the intensities at wavenumbers 1060 cm -1 and 1030 cm -1 increase. This is an indication for the formation of alkyl-alkyl ethers or for the formation of primary, as well as secondary alcohol functions. Presumably, the formation of alkyl-alkyl ethers predominates, since on the one hand there is no significant increase in OH absorption from 3500-3000 cm -1 , and on the other hand the degree of depolymerisation is kept within limits, as shown by the GPC data.