Effect of a UV/Ozone Treatment on Siloxane-Containing Copolyimides:  Surface Modification and Gas Transport Characteristics

We have prepared poly(imide siloxane) (PIS) films having various siloxane contents using a two-step polymerization technique and subjected them to a UV/ozone treatment using UV excitation in the range λ = 185−254 nm to form an SiO x layer on the surface of the PIS films. From electron spectroscopy chemical analysis (ESCA), we have confirmed that the PDMS surface layer in the PIS films converts into silica as the UV/ozone treatment time increases. Solid-state 29Si NMR provides evidence that the PDMS and silica coexist in the bulk. Gas permeation experiments on non-UV/ozone-treated and on UV/ozone-treated PIS films were carried out using helium (He), oxygen (O2), nitrogen (N2), and carbon dioxide (CO2) penetrants. For PIS films having a high siloxane content (i.e., a volume fraction of 0.457), the UV/ozone treatment decreased the gas permeabilities, but increased the selectivity of several gas pairs owing to the formation of a dense silica layer, which increased with increasing treatment time.