Polymers of Intrinsic Microporosity- Molecular Mobility and Physical Aging Revisited by Dielectric Spectroscopy and X-Ray Scattering

Polymer of Intrinsic Microporosity (PIMs) are promising candidates for the active layer in gas separation membranes due to their high permeability and reasonable permselectivity. However, this class of polymers suffers from a significant decrease in separation performance with time due to physical aging. The initial microporous structure approach a denser state via local rearrangements, leading to a reduction of the permeability. In this work, the dielectric behavior of PIM-1 films and their behavior upon hating (aging) were revisited by isothermal frequency scans during different heating/cooling cycles over a broad temperature range between 133 K and 523 K by Broadband Dielectric Spectroscopy. In addition, the obtained results were compared with data of samples that were annealed at ambient temperatures over different time scales. Multiple dielectric processes were observed: several relaxation processes due to local fluctuations and a Maxwell-Wagner-Sillars polarization effect related to microporosity¹. The temperature dependence of the rates of all processes follows the Arrhenius law where the estimated activation energy depends on the nature of the process.

SAXS/WAXS patterns were measured as a function of temperature during heating/cooling in a temperature range corresponding to that covered by dielectric spectroscopy. The influence of the aging on the processes is discussed in detail.

References

1. F. Emamverdi et al., Macromolecules 2022, 55, 7340–7350