Photodegradation of poly(ether sulphone) Part 1. A time-of-flight secondary ion mass spectrometry study

An extensive study of the surface chemical changes to poly(ether sulphone) (PES) ultrafiltration membranes is made for the first time by the use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) after photoirradiation at 254 nm with irradiances varying from 10 to 300 mJ cm^-2 in a nitrogen atmosphere. Complementary information is provided by analysis with x-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The versatility, superior specificity and sensitivity of using ToF-SIMS to investigate degradation phenomena are highlighted. The combined results demonstrate that photoirradiation causes a number of chemical changes to the surface: incorporation of oxygen; degradation of the benzene rings and formation of oxidized carbon species; depletion of carbon; reduction of -SO₂- to some extent; formation of -OH, C=O and -SO₃H groups; and probable formation of -C₆H₄-O-C₆H₅ end-groups. In addition, no -OSO₃H groups are formed and no formation of SO₂ is detected. Also, it is shown that chain scission dominates below an irradiation dose of ∼200 mJ cm^-2 (at 254 nm in a nitrogen atmosphere). At higher doses, cross-linking becomes dominant.