CAREER: Development of Catalytic, Sulfur-Free Chain Transfer Agents to Improve Mechanical and Material Performance of Crosslinked Photopolymers

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With funding from the Chemical Catalysis (CAT) and Macromolecular, Supramolecular, and Nanochemistry (MSN) Programs of the Division of Chemistry (CHE), and the Polymer Program of Division of Materials Research (DMR), Brady Worrell of the University of Denver will develop a catalytic, sulfur-free chain transfer agent (CTA) for efficiently creating photopolymers. An important subset of plastics is photopolymer, or crosslinked materials created with light. Photopolymers make up the polymer component of materials commonly used in 3D printing, dentistry, and biomaterials, however, only a limited window of mechanical properties can easily be accessed from available chemical feedstocks. In the work proposed here, Dr. Worrell and his team will create catalysts that have the potential to significantly alter the mechanical properties of photopolymers while keeping 99% of the chemical composition the same. Dr. Worrell will also establish and run the Summer High school Internships: New Experimentalists at University of Denver (SHINE @ DU) program, which aims to offer local, under-represented high school students real-world research experiences hosted in the Department of Chemistry & Biochemistry. An undergraduate led online journal detailing scalable, simple, and inexpensive preparations of organic polymers is to be established as part of this CAREER award effort.The materials generated by photopolymerization are inherently highly crosslinked and suffer from significant shrinkage stress, are often brittle, and have a limited range of material properties. Various classes of chain transfer agents (CTAs) have been investigated and developed to reduce the crosslinking density of photopolymers. Although CTAs are successful in manipulating the mechanical properties of photopolymers, they are required in high loadings (up to 20 wt% of total formulation) and frequently contain sulfur which is malodorous and can create unstable formulations. Dr. Worrell and his research team are developing a catalytic, sulfur-free CTA that can be added in ppm quantities to existing commercial monomer feedstocks to create photopolymers similar to those prepared using traditional CTAs, but at 10,000x lower loadings. Several analogs of the macrocyclic cobalt(II) catalyst will be explored to improve resin solubility and various ligands will be screened in a high-throughput fashion in the search for potent catalyst:ligand combinations. These catalytic CTAs will be tested in commercial 3D printing resins and liquid crystal elastomers to narrow and reduce the glass transition temperature, reduce storage modulus, and alter other pertinent mechanical properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.