CAREER: Design Principles for Controlled Cyclic Polymer Synthesis

University Of Washington, Seattle WA

Investigators

Abstract

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Professor Matthew R. Golder of the University of Washington is developing new synthetic approaches for the preparation of cyclic polymers. Compared to other polymer classes, cyclic polymers are unique because they lack chain ends. Cyclic polymers are currently being explored as potential candidates for next generation of drug-delivery agents, conductive materials, and thermoplastic resins. The synthesis of cyclic polymers in high purity and large quantities remains a challenge in polymer chemistry because current methodologies typically yield mixtures of linear and cyclic macromolecules which are difficult to separate. In this research, metal initiators based on ruthenium will be developed and used to control the synthesis of cyclic polymers. Detailed kinetic and mechanistic studies will be conducted to correlate the initiator structure with its reactivity in polymerization reactions. Ultimately, the developed initiators will be able to regulate reaction kinetics and molecular weight or size of cyclic polymers. If successful, this work will enable the preparation of cyclic polymeric materials with architectures that are otherwise very challenging to achieve. The research activities associated with this award will increase broadening participation and enable training of high school, undergraduate, and graduate students in synthetic polymer chemistry. The outreach program “Husky at Home Science” will reach and engage homeschooled students across the state of Washington. This activity will develop a virtual hands-on program and a children’s storybook centered around polymer science. This project will focus on the development of ruthenium-mediated ring expansion metathesis polymerization for the controlled synthesis of cyclic polymers. In the first goal, tethered ruthenium benzylidene initiators will be prepared and used to study polymerization reaction kinetics. Computational modeling will be utilized to complement the experimental synthetic and mechanistic studies. Emphasis will be placed on determining the role of initiator structure on the overall reaction profile. In the second goal, systematic studies will be conducted to gain control over the ring-closing (i.e., back-biting) of the cyclic ruthenium species relative to insertion. Decoupling monomer insertion from ring-closure could enable living polymerization in which the molecular weights of cyclic polymers will be predetermined by the ratio of monomer to the initiator. Lastly, a methodology will be developed for more accurate determination of acyclic impurities amongst cyclic polymers in ring expansion metathesis polymerization. The new technique will involve incorporation of bulky silyl ether monomers that act as single-addition degradable junctions, allowing for the union and separation of two polymer blocks. If successful, this research will advance fundamental understanding of how to control back-biting reactions in metal-mediated ring expansion metathesis polymerization, enabling the synthesis of cyclic polymers that are otherwise difficult to prepare using existing methodologies. 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.