(693a) Mitigation of Physical Aging in Microporous Polymer Membranes: Insights from Molecular Dynamics Simulations

Glassy polymers have emerged as preferred materials in gas separation membranes due to their superior selectivity compared to rubbery polymers. However, structural relaxation, which is accompanied by an increase in density and a reduction in free volume — a phenomenon known as physical aging — leads to a decrease in permeability. This decrease significantly affects membrane productivity, typically occurring within the first few weeks of operation. To address this inherent phenomenon, a hyper-crosslinked, functional porous polymer network (PPNs) based on iptycenes and activated ketones was modelled via molecular dynamics (MD) simulations. Subsequently, it was blended with PTMSP (poly trimethylsilyl propyne), a model microporous glassy polymer, with the aim of maximizing both permeability and selectivity while mitigating physical aging. The average cavity sizes of polymer membranes calculated from MD simulations are in good agreement with experimental observations. Different sizes of free volume cavities are available in neat PTMSP and PTMSP-PPN blend. Monitoring the physical aging of neat PTMSP and PTMSP-PPN blends involved measuring the pure gas permeability of N₂, CH₄, and CO₂. Reductions in gas permeability and selectivity were observed due to blending. The resistance to physical aging observed in PTMSP-PPN blends is attributed to the potential interlocking effect exerted by the PPN network on the PTMSP backbone, which reduces their mobility. Additionally, the relatively open three-dimensional network of the PPN provides permanent channels for gas transport. The study provides molecular insights into the impact of porous polymer networks on the performance of PTMSP, which could be valuable for identifying membrane materials capable of achieving efficient separations while maintaining their effectiveness.