Development of Organic Photoredox-Mediated Ring-Opening Metathesis Polymerization through Expanded Functionalities of Initiators and Monomers
Ring-opening metathesis polymerization (ROMP), which is derived from transition-metal-based olefin metathesis, has evolved into one of the most prevalent technologies for making functional polymeric materials. Due to the nature of this polymerization method, the metal alkylidene remains covalently bound to the polymer chain end until the introduction of various quenchers to terminate the polymerization. However, the removal of resultant metal by-products requires multiple purification steps. Recently, our group pioneered establishment of organic photoredox-mediated ROMP (o-ROMP), which is driven by the motivation of developing a metal-free alternative to traditional ROMP. This thesis aims to contribute to the study of o-ROMP by describing our investigations in the field, with a particular emphasis on expanding scopes of functional initiators and monomers. Chapter 1 is an introduction to o-ROMP, which start with explanation of community interests on developing organic photoredox-mediated controlled polymerization (OPCP). The general mechanisms of these novel polymerizations, including the properties of various organic photoredox catalysts, will be reviewed first. The flowing discussion will focus on different kinds of established OPCPs, which emphasizes on unique scopes for each specific methods. We will end up the introduction part with our previous efforts on developing o-ROMP. Chapter 2 begins with our initial attempts on testing the feasibility of grafting o-ROMP from small-molecular multitopic initiators. The successful combination of this multidirectional growth mode with the design of macroinitiators facilitate preparation of polyether-based triblock copolymer and polystyrene-based graft copolymer, which are both acid cleavable. Chapter 3 describes our recent efforts on expanding the scope of macroinitiator towards polyesters and polycarbonates, which are derived from organocatalyzed ring-opening polymerization (o-ROP). Grafting from bifunctional initiators in one pot, stepwise o-ROP and o-ROMP succeed in making biocompatible block copolymers via a completely metal-free pathway. Finally, Chapter 4 discusses our ongoing efforts in the expansion of monomer scopes, aiming to make functional polymers solely through o-ROMP strategy. The successful adoption of those deprotection-free functional monomers not only make it possible to enable post-polymerization modification, but also provide opportunity to control chain architectures of resulted polymer.
- Chemistry