CROSS-LINKING OF POLY[1-(TRIMETHYLSILYL)-1-PROPYNE] MEMBRANES USING BIS(ARYL AZIDES)

Cross-linkable poly[1-(trimethylsilyl)-1-propyne] (PTMSP) films were c ast from toluene solutions containing PTMSP and either 4,4'-diazidoben zophenone or 4,4'-(hexafluoroisopropylidene)diphenyl azide. The compos ite films were clear and homogeneous and were cross-linked by UV irrad iation at room temperature or thermal annealing at 180 degrees C. Low levels of the bis(aryl azide) (1-5 wt%) were effective in rendering th e films insoluble in toluene and THF, both good solvents for PTMSP. Th e process is simple and effective, and thus PTMSP can be readily conve rted to mechanically stable membranes with permeabilities and separati on factors comparable or higher than those of poly(dimethylsiloxane). The films were characterized by measuring their density, their permeab ility toward O-2 and N-2, and their spectroscopic properties. Compared to PTMSP, films containing bis(aryl azide) cross-linkers had lower pe rmeabilities and higher separation factors, consistent with a reductio n in free volume. When the films were cross-linked photochemically, th e permeabilities declined further and the separation factor increased. Films cross-linked thermally had permeabilities comparable to their P TMSP/azide precursors, and density and swelling measurements suggest t hat higher free volumes are obtained in thermally cross-linked films. All films stored in air suffered from a slow decline in permeability w hich may reflect slow surface oxidation of the films. When stored in v acuum, cross-linked films were stable and showed no loss in permeabili ty, but the permeability of uncross-linked PTMSP films stored under th e same conditions fell to 70% of their original value in 1 month. We a ttribute the permeability decline to densification accelerated by impu rities and solvents. (C) 1998 John Wiley & Sons, Inc.