Direct dehydration polycondensation of lactic acid catalyzed by water‐stable Lewis acids

Abstract

Abstract Poly( L ‐lactic acid) (PLLA) is generally produced by ring‐opening polymerization of ( S , S )‐lactide, which is prepared from dehydration polycondensation of lactic acid and successive depolymerization. Results of this study show that scandium trifluoromethanesulfonate [Sc(OTf) 3 ] and scandium trifluoromethanesulfonimide [Sc(NTf 2 ) 3 ] are effective for one‐step dehydration polycondensation of L ‐lactic acid. Bulk polycondensation of L ‐lactic acid was carried out at 130–170 °C to give PLLA with M n of 5.1 × 10 4 to 7.3 × 10 4 (yield 32–60%). The solution polycondensation was performed at 135 °C for 48 h to afford PLLA with M n of 1.1 × 10 4 with good yield (90%). In no case did 1 H NMR, specific optical rotation, or DSC measurement confirm racemizations. The catalyst was recovered easily by extraction with water and reused for polycondensation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5247–5253, 2006