Modified polysulfones 5: Synthesis and characterization of tetramethyl polysulfones containing trimethylsilyl groups and their gas transport properties

Abstract

Polysulfones with rigid backbone structures and silyl-containing substituents were prepared as membrane materials with potentially enhanced gas transport properties. Tetramethylbisphenol-A polysulfone (TMPSf) and tetramethylbiphenol polysulfone (TMPPSf) were made by polycondensation then post-modified to introduce trimethylsilyl (TMS) groups by bromination and lithiation methodology. Substitution of high levels of TMS groups at the ortho-sulfone sites was achieved using direct lithiation followed by addition of a trimethylsilane electrophile. In an approach to increase the overall TMS substitution level as well as introduce these groups on the bisphenol segment, both TMPSf and TMPPSf were cleanly brominated to a degree of substitution (DS) of 2.0 for bromine. While the subsequent lithium-halogen exchange and reaction with TMS electrophile did not give high regioselectivity because of steric hindrance, the overall DS of TMS in the polymers was increased when excess n-butyllithium was used to activate both brominated and ortho-sulfone sites. The polymer structures were characterized by NMR spectroscopy. Their thermal properties as well as O-2, N-2, CO2 and CH4 gas transport properties were measured. Polymers with a high DS of TMS had very high CO2 and O-2 permeabilities and good permselectivities from N-2. The permselectivities of CO2/N-2 were at or close to the Robeson upper-bound performance line. (C) 2002 Published by Elsevier Science Ltd.