writer：Weichao Wang, Linbo Wu*, Yuan Huang, Bogeng Li
keywords：melt polycondensation，poly(L-lactic acid)，1,3-dialkylimidazolium salts， ionic liquids
source：期刊
specific source：SaltsPolymer International, 57(6): 872-878, June 2008
Issue time：2008年

BACKGROUND: In syntheses of biodegradable and bioresorbable polymers, efficientmetal-free catalysts are very desirable as the resulting products may be more biocompatible. As an attempt to find new metal-free catalysts, 1,3-dialkylimidazolium salts, the most commonly used ionic liquids or organic melt salts, were used as singlecomponent catalysts in the melt polycondensation of L-lactic acid for the first time. The resulting poly(L-lactic acid) (PLLA) was characterized using gel permeation chromatography, 13C NMR, DSC and polarimetry.
RESULTS: It has been found that less bulky substituents on the imidazolium ring are conducive to catalytic activity. PLLA with molar mass of about 20 000 g mol−1 was synthesized at high yield (over 70%) in the presence of various 1,3-dialkylimidazolium salts. The product exhibits satisfactory color (white to slightly yellow), optical purity (89–95%) and crystallinity (40–55%). A possible catalytic mechanism is proposed.
CONCLUSION: As compared with the well-known binary catalyst system SnCl2 · 2H2O/toluene sulfonic acid, the catalysts used in this investigation are better in terms of increasing PLLA yield and preventing discoloration and comparable in terms of racemization.