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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.

One of the long-term goals of polymer chemistry is to develop techniques for synthesis of polymers with exact molecular weight (MW) along with precise control over microstructure. Recently, a new approach based on template polymerisation and block copolymers (BCP) self-assembled into nanoreactors has been reported [McHale et al, Nature Chemistry. 2012, 4 (6), 491 497]. The method utilises a combination of hydrogen bonding templated radical polymerisation (TRP) within micellar nanoreactors to synthesise daughter polymers of high MW with low dispersity. Size exclusion chromatography (SEC) analysis of the TRPs in nanoreactors show the daughter polymer eluting as a secondary peak before the elution of the BCPs that are used to form nanoreactors and act as templates. In this work, the ability of BCPs to self-assemble into nanoreactors suitable for template polymerisation is investigated with respect to block lengths and overall MW of BCPs, as well as type of solvents and temperature. TRP in nanoreactors is subsequently investigated through modification of various physical-chemical parameters (solvent and BCP chain lengths and composition), and kinetic parameters (temperature, time, monomer, monomer concentration and initiator concentration of polymerisation) to provide insight into the polymerisation mechanism. SEC, 1H nuclear magnetic resonance (1H NMR) and dynamic light scattering (DLS) investigations of various TRPs in nanoreactors clearly demonstrated that the secondary SEC peak, originally attributed to pure daughter polymer, is in fact consisting of nanoparticles of daughter polymer and the template BCPs. Despite the claims of the original work being invalidated, the results of this study did imply that polymerisation via a templating mechanism within segregated micellar nanoreactors is occurring and further work is necessary to elucidate the product of the polymerisations.

Metal-mediated reversible deactivation radical polymerization (RDRP) is now a cornerstone of functional polymer synthesis, dominated by copper complexes and the Atom Transfer Radical Polymerization (ATRP) moniker. A limitation of this approach is the contamination of the resultant polymers by the coloured copper complexes, thus requiring further purification, although protocols to reduce the amount of copper catalyst have been developed. Iron is an interesting alternative because of its low cost, low toxicity and reduced intensity of its optical absorption spectrum. Use of this metal in RDRP began in the late 90s and has continuously intensified. This review comprehensively covers all the work reported so far on RDRP mediated by iron complexes, organized according to ligand type, and discusses the specificities of this metal in terms of the multitude of accessible spin states and the interplay of different equilibria: atom transfer vs. direct radical trapping, associative vs. dissociative exchange, chain transfer by direct beta-H atom transfer vs. beta-H elimination from the dormant alkyl species. (C) 2014 Elsevier Ltd. All rights reserved.