Career: Photopolymerization of cyclic disulfides

Professor Josh Worch of the Virginia Polytechnic Institute and State University is supported to develop methods to make recyclable photopolymers known as polydisulfides. Photopolymers are polymers that respond to light, where exposure to light triggers a chemical reaction to transform, or cure, a liquid resin into a solid material. While photopolymers are an important manufacturing technology in many industries ranging from 3D printing to packaging and healthcare, conventional photopolymer resins are regarded as single-use materials since exposure to light results in irreversible chemical bonding. This research will create dynamic photopolymers containing reversible chemical bonds which enable their reusability. To achieve this goal, photopolymer composition and reactivity will be investigated to link molecular structure to material performance and recyclability. Thus, this research will have significant implications for creating better materials to be used in advanced manufacturing technologies, particularly in the rapidly growing 3D printing industry. The educational component of this proposal will introduce students across all age groups, from pre-K to undergraduate students, to photopolymers and their fabrication processes. A key activity will be to deploy pre-assembled demo boxes to local schools for students to learn about the chemistry of photopolymers and engage with advanced manufacturing technologies through hands-on activities. The Worch lab will investigate the photopolymerization of cyclic disulfide monomers to develop curable photopolymer resins that have closed-loop recyclability. Photochemical initiation will be used to trigger ring-opening polymerization (ROP) of the cyclic disulfides and produce dynamic polydisulfides which are capable of chemical recycling to monomer (CRM). Through a physical organic chemistry approach, comprehensive structure-reactivity-property relationships will be developed by determining how ring-size and stereoelectronic effects from ring substituents impact ROP of the monomer and subsequent ring-closing depolymerization (RCD) of the polymer. Thermomechanical properties of the materials will be measured and correlated to polymer microstructure. The kinetics and thermodynamics of polymerization will be studied using different modes of photochemical initiation by employing various radical, cationic, and anionic initiators to elucidate how the nature of the propagating species impacts monomer-polymer equilibria and rates of polymerization. This research will elucidate the fundamental chemical reactivity of polydisulfides to enable their future translation into recyclable photopolymer resins for advanced additive manufacturing processes; this will be impactful as the development of new resin technologies is a current bottleneck in the 3D printing industry. 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.