Biobased Cyclic Polycarbonate: Synthesis and Applications via Dynamic Bis(hindered amino)disulfide Linkers

Cyclic polymers have garnered significant interest due to their unique structure; however, their synthesis remains challenging, often hindered by low yields and limited selectivity. Considering that the cyclization step during the synthesis of cyclic polymers is presumably the most challenging, using a spontaneous and selective cyclization system is ideal. Here, we present a topology transformation from linear to cyclic, which is achieved through the error-checking ability provided by the dynamic covalent bonding between bis(2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS) and its stable radicals with a high bond exchange rate. When applying this method to biobased poly(isosorbide carbonate) (PIC), an attractive alternative to conventional petroleum-based polycarbonates, high-molecular-weight cyclic polymers were unexpectedly obtained. Since the functionalization of PICs has been traditionally limited to copolymerization techniques, we aimed to introduce dynamic covalent bonds to establish novel functionalization methods for PICs. Interestingly, the synthesis of cyclic PICs through intramolecular cyclization using dynamic covalent bonds in a heterogeneous system proceeded via a ring-expansion polymerization-like mechanism, affording high-molecular-weight cyclic polymers consisting of a PIC backbone and BiTEMPS units as dynamic units. The resulting PIC-based cyclic polymers with BiTEMPS units were applied to bond exchange reactions, providing an effective approach for the synthesis of cyclic block polymers and end-functionalized linear block polymers with a PIC skeleton. These results demonstrate the potential of dynamic covalent chemistry in polymer synthesis.