Photoinitiated Interpenetrating Triazole-Methacrylate Networks
Chris Kloxin, University of Delaware
Abstract: The photoinitiation of methacrylate-based monomers is used in a wide range of applications, from dental composites to 3D printing. Exhibiting rapid reaction kinetics, multifunctional monomers typically leads a vitrified solid with excellent mechanical properties; unfortunately, many of these materials are also brittle. The photoinitiated copper(I)-catalyzed azide-alkyne cycloaddition (photo-CuAAC) reaction also exhibits rapid network formation, but also possesses enhanced toughness. Here, we exploit the reaction orthogonality between the CuAAC and methacrylate chemistries to form a novel interpenetrating network. CuAAC and free-radical methacrylate polymerization is simultaneously triggered using a Norrish Type II photoinitiating system (photosensitizer and co-initiating tertiary amine), which is activated using blue-light to produce a glassy (modulus >2GPa), transparent, and defect-free material. The resulting mechanical properties exhibit clear contributions from the two networks: the glass transition temperature and rubbery modulus of the CuAAC network are enhanced by the incorporation of the methacrylate network, and the brittleness associated with the methacrylate is toughened by the CuAAC network. Overall, this work highlights that the functional group tolerance and simplicity of the photo-CuAAC reaction in concert with free-radical polymerization provides an effective route to design and synthesize glassy and tough polymers networks for a variety of applications, including photolithographic resists, 3D printing, coatings, and medical implants.