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Chapter 1. The introduction provides an overview of additive manufacturing as well as the material systems and photochemical processes that enable additive manufacturing. An emphasis is placed on work done to regulate free radical polymerization via addition-fragmentation chain transfer (AFCT) and reversible addition-fragmentation chain transfer (RAFT), and their applications in photopolymer networks to improve material properties and introduce novel functional materials to additive manufacturing.
Chapter 2. In this work, we incorporate a RAFT agent into a crosslinker to make chain-transferring crosslinkers, or Transferinkers, and investigate their effect on photopolymer networks. Transferinkers were shown to improve the tensile toughness of acrylic photopolymer resins by up to 100% without incurring significant loss in strength. In addition, we exploited the unique reactivity of the RAFT agent to induce accelerated degradation of the thermoset acrylic network. Reduction in kinetic chain length caused by transferinkers is observed experimentally and in simulations. As such, transferinkers are shown to be an effective and translatable strategy for developing sustainable photopolymer networks with improved mechanical properties.
Chapter 3. We report the isolation and structural elucidation of 3,3,8,8-tetramethyl-1-oxa-4,6,9-trithiaspiro [4.4] nonane-2,7-dione, an unexpected product obtained during the synthesis of functionalized trithiocarbonate RAFT agents. A spirocyclic structure was proposed, and confirmed with X-Ray crystallography. This molecule can undergo ring opening when treated with a nucleophilic amine to form a trithiocarbonate, which can be used to mediate RAFT polymerization. Potential applications in synthesizing polymers with defined head groups are also explored.
Chapter 4. We report a new class of supramolecular polymer metal-organic cage (polyMOC) gels based on the assembly of Cu24L24 cuboctahedra. We demonstrate how these polyMOCs can be reversibly photoswitched between three oxidation states (Cu(II), Cu(I), and Cu(0)) that each give rise to unique properties. Cu(II) polyMOC can also be applied to direct ink writing (DIW) 3D printing. Cu(II) polyMOC containing polymeric azides and alkynes precursors can be extruded, where the mechanically robust polyMOC serves as a template. Subsequent photoswitching to the Cu(I) state crosslinks the precursors and re-oxidation provides MOC-interpenetrating networks (MINs). In addition, the Cu(II) polyMOC can be completely removed with competing ligands to expose the nascent covalent network. |
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