Guest-host and functionalized side-chain azopolyimide membranes for controlled gas separation

This paper presents two series of azopolyimide membranes containing 4-[4-(6-hydroxyhexyloxy)phenylazo]benzene. The azobenzene groups are located as either covalently-bonded side groups or molecularly dispersed in polymer (host) matrix. The prepared azopolyimides exhibit a high stability of cis isomers, where the return reaction from cis to trans is not completed 7 days after switching off the excitation light. The incorporation of azo moieties as both side-chain groups and a dispersion in a polymer matrix decreases membrane gas permeability while increasing or maintaining selectivity for O-2/N-2, He/N-2, and CO2/N-2 gas pairs. The advantage of the azopolymers is the large difference in their permeability for CO2 and O-2 after light irradiation (permeability changes up to 29%). These large light-induced changes in the permeability of trans- and cis-azomembranes along with a slow reversible cis-trans reaction may be of interest for use in applications where long-term stability of photoinduced properties is necessary i.e. for control dosing of gases.