Thermally stimulated cascade reaction polymer membranes: a promising strategy for an increased hydrogen and propylene purification performance

Thermally stimulated solid-state reactions, forming polybenzoxazoles, from polyimides were reported about two decades ago, and introduced as promising membrane materials by Park et al. in 2007 Meanwhile most of the reported materials still suffer from low conversions at 400 degrees C and high TRonset temperatures, or low gas permeabilities, as a result of the increasing flexibility to compensate required annealing temperatures. In our study, we present a comprehensive structure-property-performance relationship, based on thermal-, film- and gas separation investigations, supported by molecular modelling and quantum mechanical simulations. Moreover, the execution of the TR process and other thermally triggered structure formations was performed within a molecular dynamics simulation for the first time. This was done in an amorphous cell and its properties, such as the free volume element characterisation with respect to a structure-property analysis done. Our materials provide among the lowest reported TR temperature and the lowest ever reported onset temperature (gamma E-PI) for a 6FDA-APAF based TRP and full conversion at 350 degrees C. beta M-PI revealed 22% of TR conversion at an annealing temperature of only 300 degrees C and 84% at 350 degrees C, leading to several upper-bound performances, an efficient hydrogen and propylene purification performance, while having a good processability and a high chemical resistance, high TR conversion at low TRonset temperatures.

Automated summary

Through molecular modeling and experimental analysis, the structure-property relationship and mechanism of thermally stimulated solid-state reactions of polybenzoxazoles were investigated. The resulting materials exhibited low conversion temperatures, high conversion rates, and excellent hydrogen and propylene separation performance, making them suitable for efficient gas separation.