Al(III)/K(I) Heterodinuclear Polymerization Catalysts Showing Fast Rates and High Selectivity for Polyester Polyols

11 January 2024

ACS Catalysis

Edward J. K. Shellard, Wilfred T. Diment, Diego A. Resendiz-Lara, Francesca Fiorentini, Georgina L. Gregory, and Charlotte K. Williams ACS Catalysis 2024 14 (3), 1363-1374 DOI: 10.1021/acscatal.3c05712

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Low molar mass, hydroxyl end-capped polymers, often termed “polyols,” are widely used to make polyurethanes, resins, and coatings and as surfactants in liquid formulations. Epoxide/anhydride ring-opening copolymerization (ROCOP) is a controlled polymerization route to make them, and its viability depends upon catalyst selection. In the catalysis, the polyester polyol molar masses and end-groups are controlled by adding specific but excess quantities of diols (vs catalyst), known as the chain transfer agent (CTA), to the polymerizations, but many of the best current catalysts are inhibited or even deactivated by alcohols. Herein, a series of air-stable Al(III)/K(I) heterodinuclear polymerization catalysts show rates and selectivity at the upper end of the field. They also show remarkable increases in activity, with good selectivity and control, as quantities of diol are increased from 10–400 equiv. The reactions are accelerated by alcohols, and simultaneously, their use allows for the production of hydroxy telechelic poly/oligoesters (400 < Mn (g mol–1) < 20,400, Đ < 1.19). For example, cyclohexene oxide (CHO)/phthalic anhydride (PA) ROCOP, using the best Al(III)/K(I) catalyst with 200 equiv of diol, shows a turnover frequency (TOF) of 1890 h–1, which is 4.4× higher than equivalent reactions without any diol (Catalyst/Diol/PA/CHO = 1:10–400:400:2000, 100 °C). In all cases, the catalysis is well controlled and highly ester linkage selective (ester linkages >99%) and operates effectively using bicyclic and/or biobased anhydrides with bicyclic or flexible alkylene epoxides. These catalysts are recommended for future production and application development using polyester polyols.