CHEMICAL SELECTIVITY AND ENERGY-TRANSFER MECHANISMS IN THE RADIATION-INDUCED MODIFICATION OF POLYETHERSULFONE

The mechanism of radiation-induced degradation of PES has been studied in a great detail by using XPS technique. PES films have been irradia ted both with 6 keV Ar and 3 keV e(-) beams. The Ar irradiation is ass umed to be representative of the processes which strictly depend on co llisional energy loss, while the electron irradiation puts in evidence mainly the processes related to electronic energy loss. In particular , three basic chemical reactions have been followed by XPS: 1) the red uction of the sulphonyl groups (-SO2-) to sulphidic-like groups (-S-); 2) the elimination of sulphur-containing groups; 3) the formation of new oxygen-containing groups, as ether, hydroxyl or carbonyl groups. D ifferences are observed when irradiating with Ar and with e(-) project iles both for the rate of evolution of the different species and for t he quantitative trends of modification. The rates of the reactions 1) and 2) are found to depend essentially on the total deposited energy. The trend and the rate of reaction 3) depend dramatically on the energ y transfer mechanism. The key factor determining the sensitivity to th e energy deposition mechanisms seems to be the inherent chemical selec tivity of the involved reactions. In particular, this means that some types of reactions are sensitive to the energy transfer mechanism due to their selectivity (as it is the case of the ''oxygen attachment'' r eactions), while others will depend only on the total deposited energy (as the sulphur loss or the sulphonyl reduction) due to the availabil ity of many concurrent pathways producing a random succession of chemi cal events yielding an unique product.