Microporous Polymers Tailored For Applications in Solution and Sustainability

Microporous organic polymers are typically insoluble materials possessing high surface areas alongside a chemically and thermally stable low density framework. As such they have been intensively studies over the past two decades towards applications in removal of pollutants from water, gas capture and storage, catalysis and more. Part B demonstrates the design and application of functionalised microporous materials applied towards sustainable applications. A sulfonated microporous polymer, synthesised using metal-free synthesis conditions is reported and applied towards the removal of heavy metals from aqueous solution. The material, SHCP-1, has a BET surface area in excess of 800 m2/g and is capable of removing over 95 mg/g of Sr and 273 mg/g of Cs in the presence of large amounts of other competing ions. In other work, a series of monomers are hypercrosslinked to yield microporous materials containing different chemical moieties and applied towards the capture of CO2 using a pressure-swing methodology. Initially the CO2 uptake of each network was measured at high pressure (20 bar) before a pressure-swing approach was applied to separate industrially relevant mixes of CO2 and N2. Networks based on carbazole, triphenylmethanol and triphenylamine were capable of converting a dilute CO2 stream (> 20 %) into a concentrated stream (> 85 %) after only two pressure swing cycles from 20 bar (adsorption) to 1 bar (desorption).

Though microporous materials can be applied towards a diverse range of applications they are not without their drawbacks. The main disadvantage of most microporous polymers is their insolubility in all common organic solvents which limits their processability and scalability. Part A of this thesis discusses work carried out on the design, synthesis and characterisation of a new class of microporous and solution-processable polymer. These materials are synthesised through the controlled radical polymerisation of a bifunctional crosslinking monomer alongside a second co-monomer. A Reversible Addition Fragmentation Transfer Polymerisation Induced Self-Assembly (RAFT-PISA) approach was applied to yield polymer nanoparticles comprised of a porous insoluble core dispersed in solution by long hydrophilic polymer chains (Figure A1.1). This allows for the design of porous colloidal suspensions that can be applied towards applications in solution.

This synthesis is reported for the first time using the monomers divinylbenzene and fumaronitrile. Fine-tuning of the reaction resulted in the synthesis of microporous materials with surface areas ranging from 270 – 409 m2/g that were capable of forming stable dispersions in various solvents. As a result of their fluorescent properties they are able to act as selective chemosensors towards nitroaromatic compounds in solution. A fluorescent quenching effect is observed when the electron-rich porous core interacts with the electron-deficient nitroaromatic compounds with a limit of detection of 170 ppb being observed. The versatile nature of this synthetic approach is demonstrated by swapping the fumaronitrile monomer for acrylic acid which still results in the formation of a porous material. The resulting material can be post-synthetically modified through exploiting the carboxylic acid moieties within the core to yield anthracene-incorporated porous materials. These porous polymers demonstrate blue fluorescence emission under UV irradiation in the visible region of light. This fluorescence alongside the porosity of the material can be exploited and used to encapsulate other fluorophores which when irradiated by UV-light give rise to a white-light emitting solution.