Isotactic polycondensation of l-lactic acid with biogenic creatinine

Isotactic polycondensation of l-lactic acid (LLA) catalyzed by biogenic creatinine was carried out at 140–175 °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). 13C 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 1H 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.