Melt polycondensation of L-lactic acid catalyzed by 1,3-dialkylimidazolium ionic liquids

作者：Wang Weichao; Wu Linbo^*; Huang Yuan; Li Bo Geng

来源：Polymer International, 2008, 57(6): 872-878.

DOI：10.1002/pi.2421

• melt polycondensation
• poly(L-lactic acid)
• 1,3-dialkylimidazolium salts
• ionic liquids

BACKGROUND: In syntheses of biodegradable and bioresorbable polymers, efficient metal-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 single-component 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, C-13 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 center dot 2H(2)O/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.

• 出版日期2008-6
• 单位浙江大学