Synopsis
Changes in the composition and structure of the surfaces of polyphenylene oxide (PPO) and polysulfone caused by UV photooxidation are followed using ESCA. The surface stoichiometry of PPO changes from CsOl to Cs04.s on photooxidation, the oxygen being added in the form of car-bony1 and especially carboxyl groups. Surface photooxidation is rapid, the ESCA spectra showing substantial changes after a few minutes of irradiation, and no further changes being detected after 10 h of reaction. The surface photooxidation of polysulfone occurs in three stages. In the first 2 h rapid oxidation takes place at carbon atoms, the levels of C-0, carbonyl, and carboxyl groups increasing at comparable rates. This is followed by slower oxygen incorporation up to 15 h of reaction, during which time carbonyl and carboxyl levels increase and oxidation of the sulfone sulfur is observed. Some degradation occurs as groups contairiing carbon and oxygen are lost from the surface.
Further oxidation then produces a decrease in the surface levels of C-0 and carbonyl groups, and further degradation. The photooxidized surface has a stoichiometry of C100& compared with C2704S in the unreacted polymer.