Surface-chemical approaches to asymmetric gas separation membranes

Abstract

Poly(4-methyl-1-pentene) (PMP) films were surface-selectively chlorinated, controlling the extent and the depth of modification with chlorine vapor pressure, photointensity and reaction time. Chlorinated PMP samples were analyzed with surface and bulk sensitive techniques to chose reaction conditions for selected modification types. Gas permeability studies with the selected membranes showed that a thick layer of densely chlorinated PMP was needed to change the gas barrier properties of a PMP membrane. The decrease in flux through the highly and deeply chlorinated PMP membrane was more pronounced in cases of large gas molecules resulting in improvements in selectivity of the membrane. PMP membranes were also surface-selectively oxidized to yield a carboxylated PMP surface (PMP-COOH). Alternating ultrathin layers of poly(allyl amine hydrochloride) (PAH) and poly(sodium styrene sulfonate) (PSS), and polyaniline (PAn) and PSS, were self-assembled onto the PMP-COOH surface. The stratification and the thickness of the layers were determined with surface-sensitive analytical techniques. The polyelectrolyte molecules were shown to be packed into the PAH/PSS multilayers in a dense and rigid manner giving improved gas barrier properties. The PAn/PSS multilayers were shown to be stratified in a similar fashion to PAH/PSS, but the molecules were bound in a loose network resulting in no changes in the gas permeability properties of the composite membranes