CAS: Diastereoselective Polymerization Catalysis for Stereo-Sequenced Polymers with Biodegradability and Chemical Circularity

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With this award, the Chemical Catalysis Program of the NSF Division of Chemistry is supporting the research of Professor Eugene Chen in the Department of Chemistry at Colorado State University. Professor Chen is designing catalyst systems for the synthesis of advanced polymeric materials that are biodegradable and chemically circular (can be deconstructed back into their component parts). The central goal of this program is to develop polymerization catalysts that can directly convert mixtures of monomer diastereomers (molecules that have the same bond connections but different three-dimensional structure) into new high-performance biodegradable materials with defined three-dimensional structure. Deconstruction of the polymers into fragments that can be joined back together into monomers is also being studied. This work is developing new catalytic processes for the atom- and energy-efficient synthesis of polymeric materials. The proposed research encompasses diverse areas of the chemical sciences, materials engineering, and sustainability, thereby providing an excellent opportunity for the training and teaching of students, including underrepresented and undergraduate students. This project also addresses the critical need to improve polymer recyclability and Professor Chen is emphasizing the importance of this sustainability issue in workshops, lectures, and presentations. New catalysts that can polymerize diastereomeric mixtures of monomers at any rac/meso ratio into stereo-sequenced polymers have the potential to transform the synthesis of high-performance crystalline materials. Diastereoselective polymerization not only avoids the material loss and added energy costs associated with diastereomeric pre-separation and purification required by traditional stereoselective polymerization methods, but also utilizes all of the diastereomers in a mixture to modulate material properties. This study is advancing diastereoselective polymerization catalysis to achieve direct polymerization of diastereomeric monomer mixtures into isotactic/syndiotactic stereo-sequenced biodegradable crystalline polymers. The approach involves designing diastereomer-selective and earth-abundant catalysts as well as examining catalyst structure–selectivity relationships via a combined experimental and theoretical approach. Furthermore, catalysis-enabled chemical circularity of the synthesized polymers is being developed to transform these materials back to their monomers, thus closing the loop of their life cycles. This program uses a rational catalyst/monomer design approach to advance polymeric materials and methodologies by emphasizing fundamental concepts related to ditacticity and diastereoselectivity. These studies serve as an excellent training ground for aspiring undergraduate, graduate, and postdoctoral chemists of diverse backgrounds.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.