Synthesis of polymers of intrinsic microporosity derived from rigid bridged bicyclic monomers for gas separation

Abstract

Polymers of Intrinsic Microporosity (PIMs) are a relatively new class of microporous materials, first reported in 2004. The rigid and contorted macromolecular structures provide PIMs with unique solution processability and high free volume, which support the rapid and selective transport of small molecules. PIMs show great potential in gas separations due to their high permeability with great selectivity. This project focuses on the synthesis of novel PIMs that can form self-standing films suitable for gas permeability measurements. The first part involves the preparation of a series of copolymers based on three naphthopleiadene (NP) derivatives. The substitution with various functional groups on the NP scaffold enabled modification of the polymer backbone, so that we could tune the physical and microporous properties. These copolymers exhibit ultra-microporosity and a large BET surface area. Robust self-standing films were obtained from these NP-based copolymers. In the second part, benzopleiadene (BP), a novel bridged bicyclic monomer composed of two catechol units and a single naphthalene core fused at two bridgehead carbon atoms, was designed and synthesised. The homopolymer (PIM-BP) was prepared based on dibenzodioxin formation. PIM-BP exhibits high permeability and remarkable selectivity for carbon capture (CO2/N2), natural gas purification (CO2/CH4) and oxygen enrichment (O2/N2). A series of copolymers composed of PIM-BP and PIM-1 were prepared. In particular, the copolymer PIM-BP75 demonstrates gas separation performance comparable to that of PIM-BP, along with improved solubility. The homopolymer PIM-BP was further modified via amidoxime functionalisation. As expected, amidoxime functionalised PIM-BP (AO-PIM-BP) exhibits ultra-high selectivities and high permeabilities for hydrogen recovery (H2/N2 and H2/CH4). In the third part, a novel aryl ether-bridged dinaphthalene (EDN) monomer, structurally similar to the NP scaffold, was synthesised. The EDN monomer was used to prepare the linear polymers (PEEK-EDN and PES-EDN), from which robust self-standing films were successfully obtained. Despite their extremely low gas permeabilities for all gases, both polymers demonstrate excellent H2/N2 and H2/CH4 selectivities above those of existing PEEK polymers. Finally, a novel dimethoxy-functionalised benzopleiadene (DMBP) monomer, structurally based on the BP scaffold, was synthesised via an intramolecular Friedel–Crafts cycloalkylation.

Polymer PEN-DHBP based on the DHBP (the demethylation product of DMBP) was prepared. Overall, this thesis focuses on a comprehensive study of the synthesis of novel monomers, highlighting their potential applications in gas separations.