Development of More Active and More Selective Catalysts for ATRP

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With this award, the Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division is supporting Professor Krzysztof Matyjaszewski at Carnegie Mellon University to develop new Cu-based catalysts for atom transfer radical polymerization (ATRP). Radical polymerization is a chemical reaction that sequentially adds small molecules of monomers to form long polymer chains that consist of hundreds or thousands of repeating units. This powerful synthetic method is used to make nearly half of all plastics, about 100 million tons worldwide each year. ATRP is a special type of radical polymerization that can prepare advanced polymers with precisely controlled chain lengths and shapes. ATRP is also used to prepare various hybrid materials by chemically linking synthetic polymers to biomolecules and to surfaces of inorganic particles. Professor Matyjaszewski’s team develops new catalysts for such important ATRP processes with enhanced activity and selectivity. This study will contribute to the creation of more precise polymers and expansion of range of polymerizable monomers, while using diminished levels of catalyst. By employing “green” ATRP catalysts, this research provides environmentally improved polymerization conditions, relevant for the industrial production of polymers. The broader impacts include the training undergraduate and graduate students in polymer science and educating the public about controlled radical polymerization via instructional webpages and videos.Under this ward, Professor Matyjaszewski and his team will explore preparation of catalysts with much higher activity than the original ATRP catalysts and that retain selectivity for the ATRP pathway while suppressing Cu-induced termination and transfer reactions. ATRP is based on a reversible atom transfer process between dormant alkyl halides and growing radicals, catalyzed by redox active transition metal complexes. ATRP is used to prepare advanced polymers with well-defined architecture. They include uniform linear chains and also star, comb and cyclic polymers, as well as statistical, periodic, gradient and block copolymers. The new ATRP catalysts are based on ligands belonging to the tris(pyridylmetyl)amine, or tetra-aza-macrocycle families. Thermodynamic and kinetic properties of new complexes will be determined through electrochemical, spectroscopic and computational methods to establish the comprehensive structure/reactivity relationship. The new catalysts being developed will be employed for ATRP of (meth)acrylates and (meth)acrylamides and also for less ATRP-active monomers such as vinyl esters and N-vinylamides. The catalysts will be evaluated for their ability to activate alkyl (pseudo)halides with F-C, N3-C, SCN-C bonds, much less active species than the alkyl bromides or chlorides that are typically used in ATRP. The extremely reactive Cu-based catalysts react not only with alkyl halides but also with propagating radicals, forming transient organocuprate species. The latter paramagnetic compounds induce termination processes. Therefore, the mechanism of Cu-catalyzed termination will be studied in great detail to gain insight into the design of more selective catalysts and optimize polymerization conditions.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.