Photodegradation of aramids. I. Irradiation in the absence of oxygen

The photolysis reactions of a series of isomeric fully aromatic polyamides (aramids) have been investigated in the absence of oxygen by ultraviolet and luminescence spectroscopy. Several of the aramids were found to undergo photo‐Fries rearrangements to give 2‐aminobenzophenone backbone units when irradiated either as films, fibers, or dissolved in liquids. Quantum yields for this rearrangement were low, < 1 × 10−6 mole/einstein, and increased with decreasing aramid glass transition temperature and increasing backbone mobility. The formation of gel, carbon monoxide, and a strong ESR signal were consistent with a free‐radical mechanism for the rearrangement.