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.

Automated summary

This study prepared two series of azopolyimide membranes with high stability of cis isomers and selectivity for specific gas pairs. After light irradiation, the membranes showed significant changes in CO2 and O-2 permeability, suitable for applications requiring long-term stability for gas dosing control.