M. Ulbricht et Hg. Hicke, PHOTOMODIFICATION OF ULTRAFILTRATION MEMB RANES .1. PHOTOCHEMICAL MODIFICATION OF POLYACRYLONITRILE ULTRAFILTRATION MEMBRANES WITH ARYL AZIDES, Die Angewandte makromolekulare Chemie, 210, 1993, pp. 69-95
The aim of the studies was to elucidate if it is possible to modify ch
emically the surface, and by this means specifically the ultrafiltrati
on 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 membran
e, which had been determined to be 79 m2/g measuring the 4-nitro pheno
l isotherm. With methyl 4-azido benzoate as model compound, using HPLC
analysis of extracts of membrane samples, it was possible to determin
e conversion and composition of the product mixture in the course of U
V photolysis. The photolysis rate decreased with irradiation time, aft
er 32 minutes 59% conversion were observed. Consequently, shorter expo
sure times should provide modifications exclusively near the outer sur
face of the membrane. Soluble photolysis products were the methyl este
rs of 4-nitroso, 4-nitro and 4-amino benzoic acid, resp.; the yields w
ere 3, 13, and 5%, resp. Only traces of the azo- and azoxy-compounds w
ere 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 sur
faces by the developed photo-modification strategy because the various
aromatic azides have different functional groups but analogous photor
eactivity.