Graduate Student Seminar Korina Vida Sinad

"Controlling Polymer Synthesis via Switchable Catalysis"

Having precise control over polymer microstructure to generate advanced materials remains a challenge for polymer chemists. For instance, copolymers are often prepared via sequential monomer addition which is hampered by tedious step-by-step feeding, the need for intermediate purifications and low efficiency.1 An emerging field to control polymerization reactions is switchable catalysis. This method utilizes well-designed catalysts whose reactivity can be altered when exposed to external stimuli such as chemical, electrical, thermal, photochemical or mechanical triggers.2

Light is probably the most explored external trigger due to non-invasiveness and easy handling.3 In 2018, Eisenrich and coworkers published the first report of in situ monomer sequence control by a single catalyst. They developed a photoswitchable catalyst that allowed for modulated ring opening polymerization of L-lactide. Synthesis was turned on and off by light-induced keto-enol tautomerism. This remote-controlled catalyst approach was also successful in the synthesis of copolymers of trimethylene carbonate and δ-valerolactone.4 Hern and colleagues also investigated the application of switchable catalysis in ring opening polymerization. The group demonstrated an electrochemical system that employs a redox switchable (salfan)Zr(OtBu)2 to toggle on/off the homopolymerization of L-lactide and cyclohexene oxide. This system was also found effective towards one-pot synthesis of multiblock copolymers.5 Both studies were able to obtain copolymers with narrow dispersities, indicative of controlled polymerization procedure, thus opening avenues to produce materials with tailored composition and properties.

References:
(1) Xia, X., Suzuki, R., Gao, T., Isono, T., & Satoh, T. (2022). One-step synthesis of sequence-controlled multiblock polymers with up to 11 segments from monomer mixture. Nature Communications, 13(1). https://doi.org/10.1038/s41467-021-27830-3.
(2) Teator, A. J., Lastovickova, D. N., & Bielawski, C. W. (2016). Switchable polymerization catalysts. In Chemical Reviews (Vol. 116, Issue 4, pp. 1969–1992). American Chemical Society. https://doi.org/10.1021/acs.chemrev.5b00426.
(3) Kaler, S., & Jones, M. D. (2022). Recent advances in externally controlled ring-opening polymerisations. In Dalton Transactions (Vol. 51, Issue 4, pp. 1241–1256). Royal Society of Chemistry. https://doi.org/10.1039/d1dt03471e.
(4) Eisenreich, F., Kathan, M., Dallmann, A., Ihrig, S. P., Schwaar, T., Schmidt, B. M., & Hecht, S. (2018). A photoswitchable catalyst system for remote-controlled (co)polymerization in situ. Nature Catalysis, 1(7), 516–522. https://doi.org/10.1038/s41929-018-0091-8.
(5) Hern, Z. C., Quan, S. M., Dai, R., Lai, A., Wang, Y., Liu, C., & Diaconescu, P. L. (2021). ABC and ABAB Block Copolymers by Electrochemically Controlled Ring-Opening Polymerization. Journal of the American Chemical Society, 143(47), 19802–19808. https://doi.org/10.1021/jacs.1c08648.