Abstract
Sulfonic acid-functionalized task-specific ionic liquids, named as Brønsted 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 (SnCl2·2H2O) for melt polycondensation of l-lactic acid under relatively high vacuum and temperature. Binary catalysts of BAILs and SnCl2·2H2O 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/SnCl2·2H2O, BAILs/SnCl2·2H2O 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, 13C NMR, XRD and polarimeter.
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