Development of Mixed Matrix Membranes Involving Hierarchical Iptycene Moieties for Gas Separation

The development of new membranes for energy-efficient gas separations has gained the attention of researchers over the past several decades. Numerous studies focus on designing novel polymers with the aim to overcome the limitations of an empirical trade-off between permeability and selectivity. However, another feasible route to further enhance the separation performance is to incorporate inorganic materials into select polymers, creating mixed matrix membranes (MMMs), rather than solely focusing on modifying polymer structures. Ideally, composite membranes combine the superior separation properties of inorganic fillers and the mechanical integrity and good processability of polymer matrices, synergistically leading to better performance. However, the fabrication of MMMs introduces a new set of challenges, which limit their gas separation performance. A major obstacle is the insufficient adhesion or mismatch between the filler and polymer phase that frequently result in interfacial defects like non-selective voids or less-permeable rigidified layers, leading to the separation performance of MMMs much lower than what theoretically predicts. Preparing defect-free MMMs with homogeneous nanofiller dispersion remains the major challenge in this field.

To address the interfacial compatibility issue, in this work, a series of novel MMMs were developed by incorporating selected fillers to 6FDA-TP, a triptycene-containing polyimide. The novelty of the new MMM design lies in the use of strong supramolecular interactions and nano-confinement effect to promote filler/polymer affinity and filler dispersion. Triptycene is a unique molecule composed of three benzene rings hinged on a common axis. The incorporation of these rigid, bulky moieties in the polyimides can introduce additional free volume elements with a narrow size distribution to improve permeability without loss of selectivity. More importantly, the three-dimensional framework of triptycene is able to induce supramolecular interactions and strong π-π stacking, preventing particle aggregation and promoting filler-polymer adhesion, which makes triptycene-based polyimides promising candidates for MMMs fabrication. In this dissertation, different strategies were explored to engineer the organic-inorganic interfacial morphologies to establish fundamental structure-property relationships for this new family of MMMs. The interfacial morphologies, microporosity and gas separation performance of the newly developed MMMs under a variety of conditions were systematically examined and discussed.