N-Heterocyclic Carbene-Organocatalyzed Ring-Opening Polymerization of Ethylene Oxide in the Presence of Alcohols or Trimethylsilyl Nucleophiles as Chain Moderators for the Synthesis of α,ω-Heterodifunctionalized Poly(ethylene oxide)s

Abstract

The present study describes innovations in the ring-opening polymerization (ROP) of ethylene oxide (EO) using N-heterocyclic carbenes (NHCs) as organocatalysts, which enables the synthesis of α,ω-heterodifunctionalized poly(ethylene oxide)s (PEOs). Two representative NHC catalysts, namely, 1,3-bis(diisopropyl)imidazol-2-ylidene (1) and 1,3-bis(di-tert-butyl)imidazol-2-ylidene (2), were efficiently employed in conjunction with a variety of chain regulators of general structure NuE, where Nu and E are the nucleophilic and the electrophilic part, respectively, with E = H or SiMe3 (e.g., PhCH2OH, HC≡CCH2OH, N3SiMe3, and PhCH2OSiMe3). Catalytic amounts of the NHC (typically [NHC]/[NuE]/[EO] = 0.1/1/100 in moles) were indeed utilized to trigger the metal-free ROP of EO at 50 °C in dimethyl sulfoxide, allowing the polymerization to proceed to completion. In this way, PEOs of dispersities lower than 1.2 and molar masses perfectly matching the [EO]/[NuE] ratio were obtained, attesting to the controlled/living char...