Chemical recycling of CO2-based polycarbonates to sulfur-containing polymers

The chemical recycling of CO2-based polycarbonates synthesized from mono-substituted epoxides, such as poly(propylene carbonate) (PPC), is constrained by the formation of thermally stable five-membered cyclic carbonates. Here, we propose a unique one-pot/one-step method for the quantitative chemical recycling of PPC to sulfur-containing polymers using COS as the "sulfur source". The process involves several steps facilitated by commercially available organic bases. Firstly, PPC is degraded to a cyclic carbonate, followed by decarboxylation to produce propylene oxide (PO). Next, cyclic (thio)carbonate is generated through the coupling reaction of PO and COS, followed by decarboxylation to propylene sulfide. Finally, the ring-opening polymerization of propylene sulfide yields sulfur-containing polymers. The resultant polymers possess tunable thioether (72-100%) and thiocarbonate linkages upon varying the catalyst and reaction conditions. Notably, the approach is also feasible for poly(ether carbonate)s. The work provides a "polymer A to polymer B" strategy for the upcycling of PPC to sulfur-containing polymers.