RUI: Creation and Application of Nucleophile-Induced retro Diels-Alder LinKages in Dynamic-Covalent Polymeric Systems

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In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professors Philip Costanzo and Daniel Bercovici of the Department of Chemistry at the California Polytechnic State University, San Luis Obispo, are developing synthetic approaches to prepare novel polymers that are responsive to externally applied temperatures. Synthetic polymers are commonly referred to as plastics and are widely used in our daily lives. Polymers are long chain macromolecules consisting of many repeating chemical units linked with carbon-carbon bonds. Their properties are controlled by their chemical structures which can be tailored for different applications. In this research, a number of chemically-distinct small molecules that trigger temperature response are first prepared and their physical properties investigated. These molecules are then incorporated into polymer chains at precise locations. This efficient strategy allows the design of polymer strands with chemical structures that can be pulled apart at one temperature and snapped back together at a different temperature. The chemistry associated with this award is broadly transferrable to many other polymerization systems and useful to materials chemistry and any other fields in which thermally-responsive plastics are of interest. This research is having a broader impact by providing unique opportunities for undergraduate students to receive cutting edge research training and education in organic and polymer chemistry. Apart from incorporating the results associated with this award into chemistry laboratory courses at the university, an outreach program called the Macromolecular Alliance of Community, Resources and Outreach (MACRO) is initiated. The goal of this program is to create a depository of outreach materials through which individuals can spread their passion and knowledge of science to the general population. This work is focused on the development of dynamic-covalent linkages that can be incorporated into polymer systems to enable switchability in polymer topology and bestow thermal responsive properties. Several studies are carried out in order to achieve this goal. The first objective focuses on the development of Diels-Alder linkage systems with novel dienes and dienophiles and systematic understanding of the thermal stability of the prepared adducts. In the second objective, the unsaturated adducts are undergoing 1,4-Michael addition which favors the retro-Diels-Alder cleavage followed by incorporation within polymeric structures using copper catalyzed atom transfer radical polymerization. The last aim explores dynamic covalent chemistry effects on the polymer topology and physical properties with special emphasis on responsive polymer surfactants. Using nucleophiles such as thiols to modulate bond-cleaving temperature is applicable to a variety of other polymerization techniques and has the potential to generate a wide range of new smart soft materials of industrial importance.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.