Onium Photocages for Visible-Light-Activated Poly(thiourethane) Synthesis and 3D Printing.

The lack of chemical diversity in light-driven reactions for 3D printing poses challenges in the production of structures with long-term ambient stability, recyclability, and breadth in properties (mechanical, optical, etc.). Herein we expand the scope of photochemistries compatible with 3D printing by introducing onium photocages for the rapid formation of poly(thiourethanes) (PTUs). Efficient nonsensitized visible-light photolysis releases organophosphine and -amine derivatives that catalyze thiol-isocyanate polyaddition reactions with excellent temporal control. Two resin formulations comprising commercial isocyanates and thiols were developed for digital light processing (DLP) 3D printing to showcase the fast production of high-resolution PTU objects with disparate mechanical properties. Onium photocages represent valuable tools to advance light-driven manufacturing of next-generation high-performance sustainable materials.

Hydrogen Production Using a Nickel Catalyst Combining Redox Activity and Pendent Base Effects.

With the mounting need for clean and renewable energy, catalysts for hydrogen production based on earth abundant elements are of great interest. Herein, we describe the synthesis, characterization, and catalytic activity of two nickel complexes based on the pyridinediimine ligand that possess basic nitrogen moieties of pyridine and imidazole that could potentially serve as pendent bases to enhance catalysis. Although these ligands have previously been reported to be complexed to some metal ions, they have not been applied to nickel. The nickel complex with the pendent pyridines was found to be the most active of the two, catalyzing proton reduction electrochemically with an overpotential of 490 mV. The appearance of a wave that preceded the Ni(I/0) redox couple in the presence of protons suggests that protonation of a dissociated pyridine was likely. Further evidence of this was provided with density functional theory calculations, and a mechanism of hydrogen production is proposed. Furthermore, in a light-driven system containing Ru(bpy)32+ and ascorbic acid, TON of 1400 were obtained.

Simultaneous Color- and Dose-Controlled Thiol-Ene Resins for Multimodulus 3D Printing with Programmable Interfacial Gradients.

Drawing inspiration from nature's own intricate designs, synthetic multimaterial structures have the potential to offer properties and functionality that exceed those of the individual components. However, several contemporary hurdles, from a lack of efficient chemistries to processing constraints, preclude the rapid and precise manufacturing of such materials. Herein, the development of a photocurable resin comprising color-selective initiators is reported, triggering disparate polymerization mechanisms between acrylate and thiol functionality. Exposure of the resin to UV light (365 nm) leads to the formation of a rigid, highly crosslinked network via a radical chain-growth mechanism, while violet light (405 nm) forms a soft, lightly crosslinked network via an anionic step-growth mechanism. The efficient photocurable resin is employed in multicolor digital light processing 3D printing to provide structures with moduli spanning over two orders of magnitude. Furthermore, local intensity (i.e., grayscale) control enables the formation of programmable stiffness gradients with ≈150× change in modulus occurring across sharp (≈200 µm) and shallow (≈9 mm) interfaces, mimetic of the human knee entheses and squid beaks, respectively. This study provides composition-processing-property relationships to inform advanced manufacturing of next-generation multimaterial objects having a myriad of applications from healthcare to education.