CAREER: Novel Approaches to Hyperbranched Polymers

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With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Michael D. Schulz of Virginia Polytechnic Institute and State University is developing self-condensing ring opening metathesis polymerization (ROMP) to prepare hyperbranched polymers. Highly and hyperbranched polymers are tree-like 3D macromolecules that have very different viscosity characteristics when compared to linear polymers. As a result, hyperbranched polymers have been applied in various applications ranging from their use as additives to coatings and as sensors, as high loading supports in combinatorial chemistry, and as homogeneous catalysts. In this research, inimers—small molecules that can act as both an initiator and a monomer—will first be synthesized. Structural modifications will also be conducted to optimize polymerization activity. Successfully prepared inimers will then be used in self-condensing polymerization to prepare several hyperbranched polymers with interesting structural and mechanical properties. This research has the potential to lay the foundation for the synthesis of new class of plastics with controlled macromolecular structures. The project will also serve as an excellent vehicle for training students in polymer chemistry and catalysis. A chemistry-themed educational outreach with demonstrations at the Science Museum of West Virginia will focus on polymers in the modern world and how their properties are dependent on chemical structure. A travelling kit will also be developed for visits to rural communities that are under-resourced in science education. The project will focus on controlled synthesis of hyperbranched polymers using ruthenium-catalyzed self-condensing ring opening metathesis polymerization (ROMP). The central approach will involve the preparation of latent-initiating olefin metathesis catalysts with modified benzylidene ligands that will be coupled to a ROMP monomer, producing an olefin metathesis inimer. The synthesized inimers will be systematically investigated to examine the effects of structural modification on latency control, activation, and polymerization properties. Successful candidates will then be used to prepare hyperbranched polymers. A strong focus will be on investigating the interplay among polymerization conditions, polymerization kinetics, hyperbranched structures, and strategies for end-group modification. Lastly, structure-property relationships in the synthesized polymers will be systematically investigated. This project has the potential to produce a powerful strategy to synthesize hyperbranched ROMP polymers with controlled branching, repeat-unit functionality, and end-groups.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.