Effective binary catalysts of Bronsted acidic ionic liquids and stannous chloride dihydrate for melt polycondensation of L-lactic acid

Sulfonic acid-functionalized task-specific ionic liquids, named as Bronsted acidic ionic liquids (BAILs), stable to water, vacuum and heat, have shown excellent catalysis for esterification. BAILS with imidazolium cation and different anions were reasonably applied as catalysts or cocatalysts of stannous chloride dihydrate (SnCl2 center dot 2H(2)O) for melt polycondensation of L-lactic acid under relatively high vacuum and temperature. Binary catalysts of BAILs and SnCl2.2H(2)O always presented higher catalytic efficiency compared with the single component. We carefully investigated the influences of acidity and ionic structures of BAILs, amount of catalysts and pressure on polycondensation rate and molecular weight and properties of poly(L-lactic acid) (PLLA). Compared to the traditional binary catalysts of p-toluenesulfonic acid/SnCl2 center dot 2H(2)O, BAILs/SnCl2 center dot 2H(2)O could improve the thermal properties of the products. PLLAs with high molecular weight, good crystallinity, high optical purity and regular stereostructure were synthesized and characterized by GPC, DSC, C-13 NMR, XRD and polarimeter. (C) 2017 Elsevier B.V. All rights reserved.