Synthesis of cyclic biopolymers from renewable monomers remains a big challenge because of lack of efficient catalysts. The organocatalyst of N-heterocyclic carbene (NHC), (+)-1-methyl-3-menthoxymethyl imidazol-2-ylidene, is used to prepare cyclic polylactones including poly(epsilon-caprolactone) (poly(epsilon-CL)), poly(-valearolactone) (poly(-VL)), and poly(epsilon-caprolactone-co--valearolactone) (poly(epsilon-CL-co--VL)) via zwitterionic ring opening polymerization. The NHC catalyst is founded a highly efficient organic catalyst for the polymerization. The resulting cyclic polymers show a melting temperature (Tm) in a range of 2060 degrees C, which is dramatically lower than the Tm of cyclic poly(lactide) (Tm = 120150 degrees C). The resulting copolymer, cyclic poly(epsilon-CL-co--VL) owns high molecular weight comparing with corresponding linear poly(epsilon-CL-co--VL) produced by other catalysts. The synthesized cyclic homo and copolymers were characterized by 1H-, 13C-NMR spectroscopy, gel permeation chromatography, differential scanning calorimetrythermogravimetric analysis and matrix-assisted laser desorption ionization-time of flight mass spectrometry. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013