Conducting Cyclic Polymers

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Professors Adam S Veige and Brent S Sumerlin of the University of Florida are supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry to synthesize cyclic polymers. Most plastics are composed of linear polymers (chains of relatively small molecular fragments known as monomers that are joined together). This project aims to develop a new and improved class of plastics by eliminating the polymer chain ends and creating cyclic polymers. The cyclic polymers are characterized and their properties are compared with their linear analogs. The ability to manipulate the composition and structure of polymers to yield a desired set of properties, such as strength, heat resistance and electrical conductivity, has significantly expanded the many roles plastics play in our modern industrial economy. Cyclic polymers have dramatically different properties compared to their equivalent linear counterparts. Catalyst technology developed at the University of Florida enables the efficient production of cyclic polymers. Some plastics are able to conduct electricity and are used in organic light emitting diodes (OLEDs). This project aims to create the first electrically conducting cyclic polymers. The project provides the students involved with hands-on training in modern inorganic and organometallic chemistry. Demonstrations that illustrate the principles of cyclic polymers are developed and presented to the general public during an annual Chemistry Day at the Mall event. In this project, a key catalyst which was discovered at the University of Florida will be employed for the synthesis of macrocyclic polyene polymers. The main thrusts are: 1) to maximize the conductivity of cyclic poly (acetylene-co-1-alkyne) polymers while retaining their solubility; 2) to improve conjugation by forcing the alignment of the polymer via side-chain ligation of substituted polyalkynes; and 3) to synthesize cyclic poly[n]carbon, which represents a new carbon allotrope. Conducting cyclic polymers are scarce, and the consequence of their cyclic topology on conductivity have yet to be explored. The project employs a tungsten catalyst that is capable of inserting acetylenes into a growing metallacycle. Cyclic polyacetylenes are then obtained by termination of the polymerization reaction via reductive elimination. Copolymerization of acetylene and substituted acetylenes produce free standing lustrous films that are interrogated for electrical conductivity upon doping. Substituted acetylenes are essential for creating soluble polyacetylenes; however, their incorporation into the polymer chain inherently reduces conjugation by twisting the polymer backbone. This project aims to produce conducting cyclic polymers through linking the substituents by post-polymerization functionalization to constrain the geometry of the polymer backbone. Finally, the project also aims to synthesize cyclic poly[n]carbon, which represents a new carbon allotrope. Linear poly[n]carbon is unstable unless the chain ends are functionalized. By having no chain ends it is expected that the cyclic polymer will be more stable and therefore, potentially isolable.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.