Sustainable Synthesis of Polycarbonates and Polythiocarbonates from Biomass-Based Eugenol-Furoic Acid-Derived Monomer and CO₂ and COS: Computational Insights

In recent years, chemists worldwide have made tremendous progress in synthesizing sustainable polymers using monomers derived from renewable feedstocks. This transition is driven by the continuous adverse accumulation of nonbiodegradable, petroleum-based polymers in the ecosystem, as well as achieving long-term goals such as economic sustainability and the depletion of nonrenewable resources. Herein, we report the sustainable synthesis of an epoxide monomer derived exclusively from the renewables eugenol and furoic acid and its copolymerization with CO2 and its sulfur congener carbonyl sulfide in the presence of the binary catalysts (salophen)CoX or (salen)CrX and onium salts to selectively afford regioselective polycarbonates or polymonothiocarbonates in very good yields. The use of propylene carbonate was shown to be an effective and safer alternative solvent to methylene chloride for performing these polymerization reactions. Importantly, unlike what is observed using the sterically nonencumbered propylene oxide monomer, the (salen)CoX and (salophen)CoX binary catalyst systems displayed strikingly different reactivities with the eugenol-based epoxide. That is, only (salophen)CoX was found to selectively provide polycarbonates in excellent yields under mild reaction conditions. This observation has been shown to be strongly supported by DFT computational studies, which illustrate the importance of designing catalysts with tailored ligand frameworks. TGA and DSC measurements reveal these copolymers to be stable up to 240 °C, with relatively high glass-transition (Tg) temperatures of 95 °C. The eugenol-derived polycarbonate fully degraded under basic conditions within one h at ambient temperature quantitatively to the diol, which is readily converted to the corresponding epoxide, making the copolymerization/depolymerization partially circular. On the other hand, the closely related polymonothiocarbonate is quite stable to degradation under identical reaction conditions.