Dynamic Mechanically Interlocked Rotaxane and Catenane Catalysts for Isoselective Ring Opening Polymerisation

Lead Research Organisation: University of Oxford
Department Name: OxICFM CDT

Abstract

Polymers consist of long chains comprised from many repeating smaller molecules, known as monomers. Essential in modern life, polymeric materials have extensive applications such as clothing, electronics and medicine, as their desired physical and chemical properties can be engineered by careful monomer selection. However, many polymeric materials are produced from non-renewable monomers and are non-biodegradable, raising serious environmental concerns over their future manufacture and disposal. Consequently, there is mounting public and academic interest in developing more environmentally sustainable routes to biodegradable polymers.
Polymer production requires catalysts, most commonly containing metals, to affect regulated linking of the monomer units to form the polymer chain. The environment of the metal in the catalyst, dictated by the arrangement of atoms surrounding it, plays a key role in specifying catalyst performance and selectivity. Such control is essential to form materials with well-defined properties, such as strength and temperature resistance, crucial for any given application.
Recent studies demonstrated that incorporating a metal into complex molecular architectures dramatically influences its catalytic behaviour. Mechanically interlocked molecules consist of two components, which are inseparable from each other, but not directly connected e.g. akin to links in a chain. Components bound in this manner are said to be linked by a mechanical bond.
The forced proximity of interlocked components allows for powerful interactions between them which are not observed in non-interlocked structures. Furthermore, the unique three-dimensional spatial arrangement of the components of the interlocked structure can be designed to form a host cavity into which a monomer unit binds, increasing its potential reactivity to polymerisation by placing it in a well-defined reactive environment. Such an interlocked catalyst mimics the spatially defined active sites of enzymes. Indeed, a range of interlocked structures have been shown to be catalytically active, displaying enhanced selectivity for various organic reactions compared to non-interlocked catalyst analogues. Despite this, with one exception, mechanical bonding has not been exploited for polymerisation catalysis.
This project seeks to build upon on those preliminary results, exploring the relationship between the structure of mechanically interlocked catalysts and polymer properties in order to develop a family of such catalysts for the formation of sustainable polymers.
Many conventional catalysts feature multiple catalytic components, typically either by binding two metal atoms in a rigid framework, or through the addition of a second co-catalyst to the mixture. This project will seek to demonstrate an unprecedented strategy of developing mechanically bound catalysts where all requisite components are incorporated in a single molecule. This unique approach uses the spatial constraints of interlocked systems to hold the components of the catalyst in close proximity, without using the rigid frameworks often found in two-centred catalysts. In addition, control over the relative proximity of the interlocked components may enable catalysis to be switched on-and-off selectively or for the reactivity of the catalyst to be modified on-demand, for instance by shielding and exposing different reactive sites on a catalyst framework. Switchability will allow for 'designer polymers', facilitating exquisite control over polymer constitution and properties to produce highly desirable polymeric materials derived from renewable and biodegradable monomer sources.
This project falls within the EPSRC Manufacturing the Future, Catalysis and Synthetic Supramolecular Chemistry research areas.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023828/1 01/04/2019 30/09/2027
2329690 Studentship EP/S023828/1 01/10/2019 30/09/2023 Jamie Wilmore