Radical polymerization accounts for 45% of all manufactured polymer, producing approximately 150 million tons of materials annually. These polymer products are ubiquitous in modern society and need continuous development of new radical initiators in order to meet the ever-changing demands for materials. In this dissertation, I focus on the design and evaluation of novel radical initiators to address persistent problems in the polymer field by discovering new mechanistic details about radical generation mechanisms that led to the improvement of various existing applications and enablement of new future applications.

In my doctoral studies, I first examined the mechanism of a well-known polymerization method that utilizes amine reductant and peroxide oxidant. Despite its extensive use since the 1950s, the initiation mechanism of amine-peroxide redox polymerizations (APRP) has been poorly understood and therefore, advances in this polymerization method have been largely incremental and empirically driven. Through a combination of computational modeling and experimental analysis, I elucidated the APRP mechanisms including its rate-determining step and derived a kinetic model that utilizes the computational calculation to predict experimental polymerization rates. This new mechanistic understanding was then applied to computationally design new amine reductant initiators with faster initiation kinetics, leading to the discovery of an initiator system that was experimentally proven to outperform current state-of-the-art amines by ~20-fold, making iii it the most efficient amine redox initiator to date for use in amine-peroxide redox polymerization processes.

I then evaluated structural variations in the peroxide oxidants within the framework of APRP using my previously developed kinetic model. By improving radical and anion stabilization with increased p-electron conjugation and increasing the electrophilicity of the peroxy bond with electron-withdrawing groups, I computationally designed several new peroxides and predicted that they would exhibit improved initiation rates when compared to the commonly used benzoyl peroxide. I then developed a redox-based 3D printing process with a custom direct writing printer that used an APRP redox pair optimized using my computational modeling to exploit its extremely high reactivity.

Beyond redox initiation, I also developed a unique photoinitiator based on amine-peroxide redox initiation that enables continued polymerization after irradiation is ceased, known as dark curing. The photoactivation of this initiator creates both initiating radicals as well as the amine compounds that can react with a peroxide over an extended period. This dark curing photoinitiator achieved a remarkable 25-60% additional conversion after exposure and slightly improved mechanical properties in comparison to conventional continuous photocuring, which can contribute to the homogeneity of polymers by raising conversions in initially under-cured regions. Using laboratory experiments and computational studies, I then clarified the origin of the high initiation efficiency and showed that this photoinitiator may be the most-photon-efficient photoinitiator to date.

Lastly, I expanded dark-curing photoinitiation to absorption in the visible range with a new chromophore through a series of computational predictions, including the study of positiondependent effects of substituents, electronic transitions, and energetics. A target compound was iv synthesized and optically examined to demonstrate strong visible light absorption. I then demonstrated extensive dark-curing with a high quantum yield.

All of the new initiators that I developed in my doctoral studies have unprecedented capabilities that enable innovation in polymer synthesis. For instance, bone cement adhesive polymers can be more rapidly fabricated with lower cytotoxicity from my redox initiators with higher efficiency. On the other hand, my photoinitiators can allow rapid coating of curved surfaces present in automotive or airplanes without a large oven needed for thermal curing.