The tacticity of polymers is one of the governing microstructural parameters that determines their material properties. Current methods to access stereoregular polymers are based on coordination and ionic polymerizations. However, these polymerization methods are limited to a small group of monomers. By contrast, radical polymerization is compatible with diverse chemical functionalities but provides poor stereocontrol primarily due to the challenge of controlling the stereochemistry of carbon-centred radicals. Here, by covalently tethering a rare earth cation-based Lewis acid to cobalt(III) complexes, we designed a bimetallic catalytic system to achieve stereocontrol in living radical polymerization. The interplay of pendant group–Lewis acid interaction and cobalt-mediated reversible radical deactivation within a confined space results in chain propagation through a meso-configurated radical chain end. Acrylamide monomers with diverse polar and ionic pendant groups were polymerized in a stereoregular manner with a percentage of meso diads as high as 95%. Thermo-responsive, adhesion and electrical properties of homopolymers were readily diversified by tuning tacticity without compositional variance. This method provides a diversity-oriented design platform to access polymers with broadly tunable bulk, solution and interfacial properties from single monomer feedstock through tacticity engineering.
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This project was financially supported by United States National Science Foundation (grant no. CHE-2108681). M.Z. acknowledges the support through a 3M Non-Tenured Faculty Award. J.M. Mayer and E. Stewart-Jones are acknowledged for their assistance with the variable-temperature ultraviolet-visible light measurements. We thank P. Guo for light intensity measurement, J. Yan for providing access to a cold room to carry out low-temperature polymerizations, and A. Datye and Y. Xue for help with the thermomechanical tests. We acknowledge N. Hazari, S.J. Miller, S. Lin, K. Kawamoto, Y. Gu, J. Zhao, A.N. Le and Y. Ma for helpful discussions.
X.Z. and M.Z. are inventors on a patent application (US provisional patent application no. 63/427,662) submitted by Yale University that covers the development of catalysts/initiators for stereocontrolled living polymerizations and of related tacticity-engineered functional polymers. The remaining authors declare no competing interests.
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Zhang, X., Lin, F., Cao, M. et al. Rare earth–cobalt bimetallic catalysis mediates stereocontrolled living radical polymerization of acrylamides. Nat. Synth 2, 855–863 (2023). https://doi.org/10.1038/s44160-023-00311-9
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