Polynorbornenes: Synthesis and Application as Gas Transport Membranes

Dense polymeric gas separation membranes offer a passive and energy-efficient alternative to current industrial separation methods such as carbon capture, hydrogen recovery, and natural gas purification. Polynorbornenes (PNBs) are particularly interesting as membrane materials due to the modular nature of the monomeric feedstock and the variety of appropriate polymerization techniques. For example, norbornene derivatives polymerized via vinyl addition (VA) polymerization yield polymers that maintain the bicyclic norbornane moiety within the polymeric backbone, giving rise to materials with high glass transition temperatures (T_g) and decomposition temperatures (T_d). Conversely, norbornene derivatives polymerized via ring-opening metathesis polymerization (ROMP) yield polymers with double bonds in the backbone that exhibit rubbery properties. The tunable nature of polynorbornenes (PNBs) makes these polymers attractive materials for studying the structure-property relationships that govern gas transport properties.

However, there is a significant drawback in the polymerization of norbornene monomers. Namely, they are typically synthesized via a Diels-Alder reaction that yields a mixture of endo- and exo-substituted isomers. It has been widely reported that the endo-substituted monomers are less reactive in both VA and ROMP than their exo-substituted counterparts. Additionally, the catalysts typically employed for VA have poor functional group tolerance; notably, polar-functionalized norbornenes give rise to low molar mass polymers in low yields.

Herein, I present my contributions to the scientific community’s understanding of the polymerization of polar-functionalized norbornenes and expound upon the application of VA and ROMP PNBs as dense polymeric gas separation membranes. My first project (Chapter II) explores the coordination environment of polar vs. nonpolar norbornene monomers with neutral, single-site Ni-based catalysts used for VP. In Chapter III, I investigate monomer stereochemistry effects on the gas transport properties of VA PNBs. My final project (Chapter IV) explores the incorporation of PNB synthesized via ROMP into the backbone of highly rigid polymers of intrinsic microporosity (PIMs) as segmented block copolymers and their resulting gas transport properties.