Thickness-dependent physical aging of a triptycene-based Tröger’s base ladder polymer of intrinsic microporosity (PIM-Trip-TB)

Abstract

Gas separation membranes are proving to be a sustainable method to mitigate climate change given the rising energy demand. Polymers of intrinsic microporosity (PIMs) have emerged as a novel material class for such application. Physical aging is a major concern for the growth and commercialization of these glassy polymers. Several factors play an important role in determining the effects of physical aging for a PIM film; one important parameter is its thickness. Gas transport properties of PIM-Trip-TB films of thicknesses between 20-150 µm were monitored over 150 days for physical aging and its dependence on film thickness. Over this period, thicker films had generally higher permeability, and thinner films aged faster. Although fresh films showed higher selectivity during the initial tests, no correlation was found between film thickness and selectivity after aging. In addition, physical aging was more severe and independent of film thickness for larger-sized gases. Film storing environment affected the physical aging of multiply tested samples significantly, whereas films which were not tested periodically showed very minimal aging. A more systematic approach is required to fully analyze and comprehend factors yielding this phenomenon.