Computer-Guided Design of Photocatalyst for PET-RAFT Polymerisation

Abstract

Photo-controlled polymerisation uses a photo-excited photocatalyst (PC) to reversibly and deactivate the propagating species. Under regulation by light, photo-controlled polymerisation features temporal control, spatial control, sequence control and high level of selectivity/orthogonality between different systems, leading to a range of applications in advanced macromolecular synthesis such as surface patterning, 3D/4D printing, polymeric micelles, multiblock antimicrobial polymers with precise sequences and architectures. All these unique features of photo-controlled polymerisation are largely dependent on properties and functionalities of PCs. Traditionally, the selection and discovery of appropriate PCs rely heavily on a trail-and-error approach, where extensive experimental screening is needed to identify desired candidates. To reduce costs and circumvent the challenges in laborious experimental work, a rational design strategy emerged where a new PC in application to a photo-controlled polymerisation system can be designed based on understanding of the structure-property-performance relationships. This dissertation aims to enable and streamline a general fully computer-guided rational strategy of designing an efficient and functional PC for a commonly used photocontrolled polymerisation technique, namely photoinduced electron/energy reversible addition-fragmentation chain transfer (PET-RAFT) polymerisation. This thesis starts from using naturally evolved Chl a with various functional substituents and investigating its photocatalytic performance and functionalities in PET-RAFT polymerisation. General orientations for the design of PET-RAFT PCs were inspired from this natural design. On top of this, comprehensive structure-property-performance relationships were established at the quantum chemical level as guiding principles for rational PC design of PET-RAFT polymerisation, by combining experimental and computational studies on a library of halogenated xanthene dyes. Finally, by implementing the most cutting-edged quantum chemical software packages, the fully computer-guided strategy of functional PC design for PET-RAFT polymerisation was enabled based on broadened structure-property-performance relationships. As an example, an efficient pH-switchable organic PC was designed. Application of this rationally designed PC in PET-RAFT polymerisation resulted in the first organocatalysed pH and light dual-gated controlled polymerisation.