The low temperature studies of the model compounds clearly point out the importance of intramolecular mechanisms for the photodegradation of the polymer. In addition intermolecular mechanisms can be observed but require the existence of free OH groups. This is in accordance with previous studies .
The results of the semiempirical study show that both intramolecular mechanisms are reasonable pathways for the photodegradation of the polymer PPE. After absorption of light, the primarily formed S1 state must undergo intersystem crossing to the triplet manifold and after internal conversion the system is in the lowest triplet T1 state. In this state ether bond cleavage as well as 1,5-hydrogen transfer might occur with a small or even no activation barrier.
These results have several important consequences for the attempts to stabilize PPE and to suppress its photoyellowing.