N-Heterocyclic carbene-initiated epoxide/anhydride ring-opening copolymerization: effective and selective organoinitiators for the production of various polyesters†

The present report describes the first use of unprotected and “free” N-heterocyclic carbenes (NHCs), such as IMes, IPr and air-stable Cl-IPr carbenes, as single component initiators for the alternating ring-opening co-polymerization (ROCOP) of cyclic anhydrides (phthalic anhydride, PA; succinic anhydride, SA) and various epoxides to efficiently and selectively access the corresponding polyesters in a well-defined manner and as metal-free materials. In the case of ROCOP runs with PA as the anhydride source, control experiments are in line with an initiation via ring-opening of PA by the NHC moiety, as established with the synthesis and structural characterization of the IMes-PA ring-opened product 1. The present NHC systems were further exploited as ROCOP initiators of PA and bio-sourced epoxides such as eugenyl glycidyl ether (EGE) and safrole glycidylether (SO) yielding the production of regioregular p(PA-alt-EGE) polyester, as well as p(PA-alt-SO), a novel polyester material.