Tailor made N-heterocyclic carbene (NHC) catalyst precursors namely (+) and (-) 1-methyl-3-menthoxymethyl imidazolium chloride have been synthesized in high yield with a literature modified procedure. A reaction of catalyst precursor with potassium tert butoxide in situ generates the NHC catalyst. The zwitterionic ring opening polymerization of lactide (LA) mediated by a catalytic system composed of NHC catalyst at 25 degrees C under argon atmosphere led to a cyclic poly(lactide) of a high molecular weight with a narrow molecular weight distribution. The cyclic poly(lactide) was characterized by NMR spectroscopy, Gel Permeation Chromatography (GPC) and Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The NHC catalysts are active for lactide polymerization in the presence of air and elevated temperatures at 55 degrees C. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1568-1575, 2012