International Collaboration in Chemistry: Improving Livingness by Detailed Kinetic Studies into ATRP

• Applicant: Professor Dr. Michael Buback
• Subject Area: Preparatory and Physical Chemistry of Polymers
• Term: from 2010 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 181616708

Atom transfer radical polymerization (ATRP) is among the most successful controlled radical polymerization (CRP) processes in academia and in industry. However, there are still several challenges facing ATRP. They include quest for more benign catalysts that should be less toxic (e.g. iron-based) and could be used at lower concentrations and enhanced selectivity. The improved control over ATRP should increase livingness of growing chains and reduce proportion of chains that participate in radical transfer and termination. In order to reach this goal, we propose systematic and detailed kinetic studies of model reactions and also real ATRP systems. We plan to study a series of Cu-based catalysts with significantly higher ATRP equilibrium constants, based on ligands that contain electron donating substituents and also anionically charged ligands. Such catalysts should perform better at diminished catalyst concentrations due to their higher stabilities and also higher ATRP equilibrium constants. They will be used in conjunction with various reducing agents and should be applied to polymerization of less active monomers such as vinyl acetate and to acidic monomers. We also plan to explore Fe-based catalysts, with a new series of ligands. We have successfully used Fe(II) halides in polar solvents without additional ligands to reach moderate polymerization rates. Nevertheless, new ligands are needed to further enhance polymerization rate and control. We also plan detailed studies of medium effects, including pressure, temperature and various solvents. We found strong acceleration of ATRP at higher pressure with Cu-based catalysts but a decreased rate at higher pressure for Fe-based systems. Thus, new Fe-based catalysts should be developed to provide enhanced rates at higher pressure, thus strongly improving livingness. However, at elevated temperatures, side reactions, such as transfer, self -initiation, depropagation start to operate. We would like to suppress these side reactions by pressure and solvents. ATRP equilibrium constants in water are 10,000 times higher than in acetonitrile, showing that appropriate combination of pressure, temperature, and solvent can significantly improve control over ATRP. More detailed kinetic studies are needed to comprehensively correlate medium effects and structural parameters of catalysts, monomers, growing radicals and dormant species with ATRP control and livingness. We believe that to reach these goals, it is necessary to synergistically combine the expertise of both groups, the accumulated knowledge on ATRP in the Matyjaszewski group with the expertise of the Buback group on laser-assisted methods in conjunction with EPR-spectroscopic quantification of radical intermediates and on radical polymerization systems up to high pressure.

• DFG Programme: Research Grants
• International Connection: USA
• Participating Person: Professor Dr. Krzysztof Matyjaszewski