Development of Iptycene-Containing Polysulfones And Ladder Polymers for Gas Separation Membranes

Conventional separation methods such as sorption processes and cryogenic distillation are extremely energy intensive, and membrane technology is especially attractive as an alternative due to greater energy efficiency, minimal spatial requirements, and simplicity of operation. Ideal separation membranes require high permeability (gas throughput) and selectivity (separation efficiency), which is crucial to achieve required separations. One of the greatest challenges of current polymer membranes is the inherent tradeoff between permeability and selectivity. This tradeoff originates at the molecular level, where undesired free volume architectures (small, indiscriminate microcavities) arising from random chain packing in glassy polymer membranes makes it difficult to simultaneously achieve fast and selective gas transport. Additionally, physical aging provides another challenge to overcome, as glassy polymer membranes generally exist in a non-equilibrium state upon formation, and over time the polymer chains can undergo relaxation towards a denser, equilibrium state. This process collapses free volume, reducing permeability. To combat these challenges, molecular level design of polymer membranes to incorporate bulky structures that disrupt chain packing, linkages that rigidify the backbone, and introduction of shape-persistent architectures containing configurational free volume elements is a promising strategy. The overarching theme of this work is the simultaneous development of enhanced polymer membranes for improved gas separations alongside the exploration of fundamental relationships between structural variations in polymers through the incorporation of iptycenes and their ensuing property changes. Two iptycenes, triptycene and pentiptycene, perfectly fit the aforementioned design criteria with their rigid, three- dimensional architectures containing three and five arene rings respectively, arranged in a paddlewheel-like formation (triptycene) and an extended, H-shaped scaffold (pentiptycene), and thus, their integration into polymer backbones comprises the foundation of this dissertation. Incorporation of triptycene and pentiptycene into both polymers of intrinsic microporosity (a new generation of high permeability ladder-type polymers) and polysulfones (a traditional gas separation membrane family) yielded exceptional improvements in gas separation performance due to the bulky iptycene structures and their natural free volume elements in the size-range of relevant gas pairs. Additionally, the configuration-based free volumes instilled by the iptycene units provided excellent resistance to physical aging, and in some cases, even delivered unique aging- enhanced performance.