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Browsing by Subject "photopolymerization"

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    Thermoset Films and Nonwovens via Thiol-Ene Photopolymerization
    (2021-12) Lau , Christie
    Thiol-ene photopolymerization is a simple, versatile method to form thermosets rapidly at high yields. This thesis focuses on studying the structure-property relationships of three thiol-ene photocured networks formed from biobased, dual-curable, and hybrid components. The photocurable resins were first developed through bulk studies and then applied in forming thermoset nonwovens via a simultaneous electrospinning and UV curing process. Unlike conventional fiber spinning methods, the reactive fiber spinning approach requires significantly less solvent and leads to the formation of thermoset fibers, which generally have better thermal and chemical stability compared to thermoplastic fibers. For the biobased networks, two carbohydrate-based monomers were reacted with tetra-thiols to form thermosets. The monomers had subtle chemical substituent differences yet led to unexpectedly large differences in mechanical properties that were attributed to their different molecular geometries. This study highlights an important reality when using bioderived feedstocks in that they can possess subtle chemical substituent differences that can translate to polymers with vastly different thermophysical properties. The bioderived monomers were subsequently used to form nonwovens, and the fibers readily degraded into small molecules in basic aqueous media. Dual-curable polyurethane-(meth)acrylate networks containing thermally labile urea linkages were also formed via photopolymerization. Subsequent heating triggers a network rearrangement process, facilitated in part by reactions between newly exposed isocyanates and diols, which also improves the material’s toughness. In processes that require fast reaction kinetics, such as reactive fiber spinning, monomers with high functionalities are often required and the resulting thermosets are tightly crosslinked and brittle. This dual-cure system overcomes such limitations by first setting the fiber morphology rapidly via photopolymerization and utilizing a second stimulus (heat) to transform the network, which defines the materials’ final thermophysical properties. Finally, hybrid networks containing tri-acrylates and tetra-thiols as the stiff components and polybutadiene as the elastomeric component were formed. Besides obtaining bulk hybrid thermosets with phase-separated structures, successful formation of fibers was demonstrated, which cannot be attained via conventional fiber spinning methods due to the liquid character of polybutadiene. This strategy to form fibers from materials with low Tg was also demonstrated for other elastomers, as evidenced by the successful formation of fibers containing polydimethylsiloxane.