Ring-opening copolymerization of ε-caprolactone with 2,2-dimethyltrimethylene carbonate using N-heterocyclic carbene organocatalysts

Random copolymer of epsilon-caprolactone with 2,2-dimethyltrimethylene carbonate has been synthesized by using N-heterocyclic carbene organocatalysts for the first time. A series of N-heterocyclic carbenes namely, imidazol-2-ylidenes substituted at 1,3 position by benzyl, isopropyl, ethyl and methyl were demonstrated to bring about the metal-free ring-opening copolymerization of epsilon-caprolactone and 2,2-dimethyltrimethylene initiated by benzyl alcohol in THF. The influences of reaction conditions, such as monomer, catalyst, and initiator concentration, as well as reaction temperature and time on the copolymerization have been examined in detail. The results show that 1-isopropyl-3-benzyl imidazol-2-ylidene carbene was potent organic catalyst for the ring-opening copolymerization of cyclic esters to generate well-defined linear polyesters of controlled molecular weight and narrow polydispersity. H-1 NMR spectral data of copolymer obtained showed that the polymerization mechanism is in agreement with the activated monomer mechanism.