Polymers of Intrinsic Microporosity for Heterogeneous Base Catalysis

Abstract

The climate crisis is the greatest challenge facing this generation, and in order to meet ambitious targets set by global leaders, great advancements in sustainable technologies are needed. This thesis work aimed to develop a new series of polymers of intrinsic microporosity (PIMs) for catalytic applications. PIMs have been of great interest within materials chemistry since their development in the early 2000s, they are purely organic materials that have a lower environmental impact than competing materials and can be synthesised under relatively mild conditions. More specifically, Tröger’s’ base (TB) PIMs are materials that, along with the typical high porosity of PIMs, possess two bridgehead nitrogens that can be used to tune the polarity of the final material. In this work, we have synthesised a series of novel TB-PIMs which can act as basic catalysts because of the basicity of the bridgehead nitrogens. We have demonstrated that by increasing the degree of flexibility in the polymers, we can induce a “swelling” effect that facilitates the accessibility of the catalytic sites and allows the use of larger substrates, thus increasing the catalytic performance. We have also shown that new functionalities can very easily be incorporated into PIM structures, meaning that these materials can be tailor made for specific applications. We have demonstrated that by increasing the number of basic nitrogen sites in a repeated unit, we can further increase the rate of a reaction. Finally, we have shown that post-functionalised PIMs can successfully catalyse a range of environmentally important reactions. For instance, quaternised TB polymers were successfully used to catalyse the cycloaddition of CO2 into epoxides, to form cyclic carbonates that can be employed as sustainable solvents, and sulfonated PIMs have been successful in the transesterification of oils for biodiesel synthesis. We believe that this work lays a foundation for future research into PIM catalysts, as they are a versatile, facile, robust, and efficient catalytic technology.

Advances in Polymers of Intrinsic Microporosity (PIMs)-Based Materials for Membrane, Environmental, Catalysis, Sensing and Energy Applications

“…PIMs such as PIM-1 69 and Tröger's base-based PIMs 70 ; ii) linear PIMs such as polyimides, 71 polyamides, 72 polybenzimidazole, 73 and poly (ether-ether-ketone) 74 ; and iii) hyper-crosslinked PIMs such as phthalocyanine-containing polymers. 75 For the three types of PIMs, the synthesis should involve at least two units that can polymerize with each other. For instance, to synthesize PIM-1, a nucleophilic substitution reaction should occur between units containing four hydroxyl groups and four fluorine groups acting as leaving groups (Fig.…”