Polymerization of lactic acid co-catalyzed by tin (II) chloride dihydrate and ε-caprolactam

摘要

Poly(L-lactic acid) (PLA) are biocompatible and biodegradable materials with many environmental, biomedical, and pharmaceutical applications. Much attention is devoted to polylactic acid with the decline of petroleum reserves recently and the price of poly (lactic acid) has gradually become competitive to that of the average alkene polymers. In comparison with the well-established method for the catalytic ring-opening polymerization of lactide, the direct dehydropolycondensation of lactic acid is rather difficult because of various factors, such as kinetic control, limited and inappropriate catalyst activity, and lack of suppression of depolymerization. Recently, Moon et al.[1"21 succeeded in preparing a high polymer of PLLA by direct melt-polycondensation of LA using Sn(II) compounds activated by proton acids as the co-catalysts. In our previous work, we have successfully synthesized P(D,L)LA cocatalyzed by succinic anhydride and SnCl_2-2H_2O. In this study, Polylactic acid was synthesized from commercial available cheap aqueous lactic acid (85%-90% w/w) using e-caprolactam and SnCl_2-2H_2O as catalyst in the absence of organic solvents. As a result, polylactic acid with a molecular weight of 50000 and yeild of 87-94% was prepared in 16 h. The new procedure is much simple, cheap and outstanding in that the start material is aqueous lactic acid; the catalytic system is environmentally benign.