Isotactic polycondensation of L-lactic acid (LLA) catalyzed by biogenic creatinine was carried out at 140-175 degrees C under sequentially reduced pressure (30-10 torr). The product poly-LLA (PLLA) possesses high optical purity (e.e. 96.1-98.7%) as well as narrow molecular weight distribution (PDI 1.74-1.85). C-13 NMR follow-up monitor of the polymerization demonstrated that the isotacticity of PLLA formed in the polymerization kept constant high values (isotacticity 97.8-99.5%) throughout the polymerization. The H-1 NMR structural characterization of the growing polymeric species in progress of the polycondensation revealed that the active catalytic species is a guanidinium formed in situ. A possible mechanism of the creatinine-catalyzed polycondensation was proposed. (c) 2012 Elsevier Ltd. All rights reserved.