Poly(lactic acid) was synthesized from cheap, commercially available aqueous lactic acid (85-90% w/w) with F-caprolactam and SnCl2.2H(2)O as catalysts in the absence of organic solvents. As a result, poly(lactic acid) with a molecular weight of 50,000 and a yield of 87-94% was prepared in 16 h. The new procedure is quite simple and cheap. The starting material is renewable aqueous lactic acid. The effects of the amount of the catalyst, the reaction temperature, and the reaction time on the polymerization were investigated in detail. The polymers obtained by epsilon-caprolactam and SnCl2.2H(2)O were characterized with gel permeation chromatography, infrared, and nuclear magnetic resonance. (c) 2007 Wiley Periodicals, Inc.