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Functional Microporous Organic Polymers

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Porous nano-scale structures as catalysts

Microporous organic polymers (MOPs) have pore sizes smaller than 2 nm on average. Scientists exploited their large specific surface areas in novel functional MOPs for catalysis.

Industrial Technologies

Porous polymers have generated a tremendous amount of interest for use in gas separation, energy storage and catalysis. They make possible the production of multifunctional materials with hierarchical porous architectures using the well-established and straightforward processing of polymers. Scientists launched the EU-funded project 'Functional microporous organic polymers' (FUNMOPS) to synthesise novel MOPS for catalysis. The nano-scale MOPs provide a platform for development of heterogeneous catalysts in which the catalyst is in a different phase than the reactants. The heterogeneous nature means the catalyst can be recycled. Targets included catalysts made of knitted MOPs, MOPs with both acid and base moieties, and MOPS containing photo-initiators. Knitted MOPs are produced by 'knitting' aromatic building blocks using an external cross-linker and inexpensive reactants. FUNMOPS scientists synthesised a knitted network of iron(III) phthalocyanine chloride and then copolymerised it with benzene to increase porosity. Unexpectedly, they found that surface area increased linearly with increasing benzene content. As iron(III) phthalocyanine chloride is a known catalyst of oxidation, scientists tested the benzene co-network and demonstrated excellent oxidation and product yield as well as chemoselectivity. The team also had success with acid-base catalysis in MOPS using the base-catalysed Knoevenagel (condensation) reaction of benzaldehyde with malononitrile. The team demonstrated 96 % conversion with selectivity greater than 99 % using conjugated microporous polymer functionalised with amine groups as the heterogeneous catalyst that was successfully recycled. The team also showed the utility of less expensive knitted networks for the base-catalysed Knoevenagel reaction. Finally, the team demonstrated the synthesis of MOPS containing the rigid aromatic photo-initiator thioxanthone. As in the case of the knitted MOPs, scientists produced the MOP by copolymerisation of thioxanthone with another high-yielding porous monomer. The networks were successfully used for free-radical photopolymerisation of methyl methacrylate. Further, the MOPs could be recycled without significant loss of activity. FUNMOPS has made a significant contribution to the fields of polymers and catalysis, both of great socioeconomic importance. The recyclable MOPs with high yields and high selectivities for industrially relevant reactions will also enhance the competitiveness of numerous manufacturers making products relying on catalysis.

Keywords

Catalysts, microporous organic polymers, polymers, Knoevenagel, thioxanthone

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