MTCiting: Polymer Chemistry in Chemical R&D

Various classes of polycarbonates are produced by catalytic activation of CO₂  and ring-opening copolymerization (ROCOP) with epoxides. Heterodinuclear metal complexes have proven to be very effective epoxide/CO₂ ROCOP catalysts with respect to activity and selectivity. One feature of these complexes is that their ligands that can be easily modified in order to explore structure–activity relationships. The authors point out that although almost all PO/CO₂  ROCOP catalyst development has focused on Co(III)K(I) complexes, there are a number of advantages to using sodium rather than potassium in catalysis. In this work, four Co(III)Na(I) catalysts are investigated under varying conditions for the ROCOP of PO and CO₂, with the goal of determining the optimal ligand coordination environment and operating conditions. To monitor and determine reaction rates, operando FTIR spectroscopy using ReactIR was performed directly in the reaction vessel at varying pressures and temperatures. The results showed that activity and selectivity of propene oxide/carbon dioxide ring-opening copolymerization is heavily dependent on ligand macrocycle modification. When one of the macrocycle ligand-Co(III)Na(I) catalysts was employed under conditions at higher temperatures, it outperformed the related Co(III)K(I) catalysts with respect to selectivity and activity.

Butler, F., Fiorentini, F., Eisenhardt, K. H. S., & Williams, C. K. (2025). Heterodinuclear Co(III)NA(I) catalysts for the Ring-Opening copolymerization of propene oxide and carbon dioxide. Macromolecules. https://doi.org/10.1021/acs.macromol.5c01529

Tris(pentafluorophenyl)borane (BCF) shows significant potential as a catalyst for ring-opening polymerization (ROP) of propylene oxide (PO) to yield polyether polyols with high primary alcohol (1° OH) selectivity. However, use of this catalyst is limited as a result of an undesirable side reaction in which PO isomerizes to propionaldehyde (PA). The work described in this paper investigates whether a catalyst could be designed that would decrease the isomerization of PO to PA while still maintaining high rates in the ROP of PO and high regioselectivity for (1° OH). Based on earlier developments, the researchers postulated that tris(3,5-bis(trifluoromethyl)phenyl)borane (1), which has similar Lewis acidity to BCF but is less sterically crowded about the boron center, could be effective.

Catalyst 1 and some heterotriaryl boranes were tested in the ROP of PO using a continuous flow Vapourtec microreactor. In kinetic experiments, the amounts of unreacted PO and PA present as a function of time were determined using a ReactIR system equipped with a diamond ATR flow cell. The results demonstrated that minor changes in substitution on the borane aryl rings impact both catalyst regioselectivity and isomerization of PO to PA. In support of the scale-up experiments, semi-batch polymerizations of PO were performed using an RC1 pressure reactor system incorporating a ReactIR in-situ probe. Based on these findings, the PO polymerization process was scaled up and demonstrated for catalyst 1 and the polyether polyols, producing superior polymer for flexible packaging adhesive polyurethane application. 

Raghuraman, A., Spinney, H. A., Wilson, D. R., Villa, C., Arora, S., Majumder, A., De La Hoz, J. M. M., Paradkar, M., Gies, A. P., Suzuki, M., Keaton, A., Mukhopadhyay, S., Bernales, V., Masy, J., & Kennedy, R. D. (2025). Triarylborane-Catalyzed Ring-Opening Polymerization of Propylene Oxide: A pathway to Superior Polyurethanes. Industrial & Engineering Chemistry Research. https://doi.org/10.1021/acs.iecr.5c01981