Irradiation response of ultrathin polyxanthene membranes with different interunit linkages for He separation from Kr and Xe

Interunit linkage flexibility regulates irradiation responses of ultrathin polymer membranes. • Diaryl ether linkages enable structural accommodation under γ irradiation. • PX-BPO membranes retain He and Kr/Xe separation after 50 kGy irradiation. • Crack formation causes nonselective transport pathways in rigid-linkage membranes. Efficient membrane separation of He/Kr/Xe noble gas mixtures is essential for He recycling and radioactive off-gas treatment in advanced nuclear reactors. Nevertheless, radiation induced structural degradation greatly limits the practical application of polymeric membranes in radioactive service conditions, especially for high-performance thin film composite membranes. Establishing valid molecular design strategies to suppress such nanoscale structural damage still poses a major obstacle to the development of radiation resistant separation membranes. Here, we show that ultrathin polyxanthene membranes containing different interunit linkages exhibit markedly different responses to γ irradiation. Three approximately 100 nm selective layers containing biphenyl (PX-BP), diaryl ether (PX-BPO), and hexafluoroisopropylidene (PX-HFP) linkages were evaluated for He/Kr/Xe separation after irradiation in air up to 50 kGy. At 50 kGy, PX-BP and PX-HFP developed severe cracking accompanied by substantial losses in selectivity, whereas PX-BPO underwent pronounced wrinkling while retaining selective-layer continuity and over 74% of its initial He/Kr and He/Xe separation factors. Structural characterization and molecular calculations further showed that PX-BPO underwent pronounced structural reorganization while retaining selective-layer continuity. Its diaryl ether linkage exhibited the lowest torsional barrier and a more distributed electronic and geometric response to one-electron ionization. These results identify linkage conformational flexibility as an important molecular factor associated with the distinct irradiation response of PX-BPO within this PX series. Download: Download high-res image (417KB) Download: Download full-size image