DMF/DMSO-catalyzed selective ring-opening polymerization of salicylate cyclic esters

Salicylate copolyesters are promising biomedical materials due to their biodegradability, biocompatibility, and bioactivity. Eliminating toxic catalyst/initiator residues in polymers is of great importance for their medical applications; however, achieving this remains a formidable challenge in controllable high-molecular-weight polyester synthesis in certain cases. In this work, dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) as weak hydrogen-bonding catalysts are found to efficiently catalyze the controllable ring-opening polymerization (ROP) of salicylate cyclic esters, where the phenolic ester bond in the monomer is selectively cleaved rather than that in the polymer chains. Therefore, high-molecular-weight salicylate copolyesters in a controlled manner (M _{n, PSG} = 177.5 kg mol^-1 and M _{n, PSMG} = 530.0 kg mol^-1) are successfully synthesized due to effective suppression of backbiting and intermolecular transesterification side reactions. DMF and DMSO are easily removed through devolatilization after polymerization, eliminating tedious purification steps and toxicity concerns for potential medical applications. In addition, the polymerization remains well-controlled even in the presence of water. Theoretical calculations indicate that DMF/DMSO catalyze the ROP through weak hydrogen interactions with the monomer and initiator/phenolic propagation species, which enables the selective ROP of salicylate cyclic esters.