Zwitterionic ring-opening polymerization of macrocyclic ethyleneoxy-substituted carbonate: Access to cyclic PEG-like polycarbonate

The innovation in polymer design to rival conventional polyethylene glycol (PEG) is an important ap-proach to achieving a more sustainable society. Here, cyclic PEG-like polycarbonates having high molec-ular weight (4.4-49.5 kg/mol) were enabled through zwitterionic ring-opening polymerization (ZROP) of macrocyclic carbonates (MCs) mediated by N-heterocyclic carbene (NHC). The thermodynamic behavior of polymerization depends on the ring size of monomers. During this process, the ZROP of 11-membered MC was driven by the change of enthalpy (Delta H-p) which differed from the ZROP of 14-membered MC driven by the entropic change (Delta S-p). Cyclic polycarbonates depicted improved thermostability (T-d5% >= 204 C-degrees) and higher glass transition temperatures (T-g > -40 C-degrees) in comparison to their linear analogues (T-d5%<= 185 C-degrees, T-g similar to-50 C-degrees). In addition, the mechanism of ZROP of MC was addressed through computational study. A distinct mechanism of polymerization distinguishable from the well-known NHC-mediated ZROP of cyclic esters was revealed, where the zwitterion from nucleophilic addition to MC, i.e. tetrahedral intermediate, cannot be ring-opened probably due to the delocalization of negative charge on the carbonate group, but serves as an active center for the polymerization. In comparison to PEG, the attained polymer demon-strated comparable hydrophilic and biocompatible properties, as revealed by the results of contact angle and in vitro cytotoxicity studies, suggesting that cyclic polycarbonate hold the promise as the alternative of PEG.(c) 2023 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.