Abstract: The direct polycondensation method with different catalyst was used to synthesize polylactic acid (PLA) from D, L-lactic acid, the catalytic effect of NaBr, NaCl, NaI, KI, KCl and KBr was compared. The influences of dosage of catalysts, reaction time and reaction temperature on the polymerization were discussed. The PLA was characterized using infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry and thermogravimetry. It showed that KI was the optimum catalyst. When the molar ratio of KI to D, L-lactic acid was 0.2，polymerization time was 12 h, reaction temperature was 130 ℃, the weight-average molecular weight of obtained PLA was 1.151×105 with a yield of 70.73 %. With increasing average molecular weight of PLA, the glass transition temperature increased. The thermal decomposition temperature of PLA decreased with increasing dosage of catalysts.

Key words: poly (lactic acid), potassium iodide, polycondensation, catalyst concentration, reaction time, reaction temperature, weight-average molecular