Browsing by Author "Dookhith, Aaliyah Z."

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Leveraging living copolymerizations as a tool to tailor the architecture and mechanical properties of polymer networks
(2024-05) Dookhith, Aaliyah Z. ; Sanoja, Gabriel Eduardo; Ravi-chandar, Krishnaswamy; Rosales, Adrianne M; Lynd, Nathaniel A; Page, Zachariah A
Polymer networks pervade our society in many different shapes and forms, including pressure sensitive adhesives, engineering elastomers, and biomedical hydrogels. These materials date back to the 15th century when Mayan Civilizations would react latex from rubber trees in the presence of oxygen to form a brittle and unstable rubber. It was not until many years later that Charles Goodyear substituted oxygen with sulfur that a tough and stable rubber was obtained. While this was perhaps one of the first demonstrations of how key the polymer chemistry is to the ultimate mechanical properties, centuries later, we still lack the fundamental understanding to rationally design polymer networks using polymer chemistry. This Ph.D. aims to answer this question by leveraging living copolymerizations to tune the gelation, architecture and mechanical properties of polymer networks. Living copolymerizations in the last century revolutionized polymer chemistry, and allowed for the formation of linear chains with well-defined molecular weight and dispersity. Today, a library of techniques exists to synthesize any backbone chemistry, but they remain rather underutilized for making 3-dimensional polymer networks through the copolymerization of monomer and crosslinker. Here, we focus on epoxide copolymerizations catalyzed using organo-aluminum catalysts and acrylate copolymerizations mediated by Reversible Deactivation Radical Polymerizations (RDRPs) techniques, namely RAFT and ATRP. In both systems, differences between rates of polymerization are used to tune the cluster growth rate, the architecture and mechanical properties of polymer networks. The key results from this Ph.D. are that delayed gelation observed with more controlled systems yield phase separated networks. If decomposing spinodally, these networks are stiffer, and if phase separating by nucleation and growth, they tend to be softer. Compared to their non-phase separated analogs synthesized using uncontrolled polymerizations, these materials offer a different trade-off between their small- and large-strain mechanical properties. As such, we provide engineering guidelines for designing tougher materials, to be used either in their as-synthesized state or as fillers in a multiple network architecture, for new emerging technologies.