PHOTOMODIFICATION OF ULTRAFILTRATION MEMBRANES .1. PHOTOCHEMICAL MODIFICATION OF POLYACRYLONITRILE ULTRAFILTRATION MEMBRANES WITH ARYL AZIDES

The aim of the studies was to elucidate if it is possible to modify chemically the surface, and by this means specifically the ultrafiltration properties, of polyacrylonitrile membranes using photoreactions of aromatic azides. Nine azides distinguishable by different more or less hydrophilic or hydrophobic substituents were applied. Soaking in 0.05 molar solutions of the aryl azides in methanol resulted in an uptake of 1.25 - 1.95 . 10(-4) mol/g azide in the membranes. About 1 . 10(-4) mol/g aryl azide were adsorbed onto the surface of the porous membrane, which had been determined to be 79 m2/g measuring the 4-nitro phenol isotherm. With methyl 4-azido benzoate as model compound, using HPLC analysis of extracts of membrane samples, it was possible to determine conversion and composition of the product mixture in the course of UV photolysis. The photolysis rate decreased with irradiation time, after 32 minutes 59% conversion were observed. Consequently, shorter exposure times should provide modifications exclusively near the outer surface of the membrane. Soluble photolysis products were the methyl esters of 4-nitroso, 4-nitro and 4-amino benzoic acid, resp.; the yields were 3, 13, and 5%, resp. Only traces of the azo- and azoxy-compounds were detected. It was demonstrated with the help of UV reflectance and FT-IR ATR spectroscopy, applied to photo-modified PAN membranes, that a surface functionalisation via formation of secondary amines occures. It is expected to create PAN membranes with specifically modified surfaces by the developed photo-modification strategy because the various aromatic azides have different functional groups but analogous photoreactivity.