Synthesis of poly(glycolic acid) in ionic liquids

The synthesis of poly(glycolic acid) (PGA) by polyesterification of glycolic acid was studied using ionic liquids, mainly 1,3-dialkylimidazolium salts, as reaction media. The H-1 NMR spectra of PGA oligomers were assigned and end-group signals were used to follow the reaction. Low PGA yields were obtained by the direct polyesterification of glycolic acid at 200-240 degrees C, because of monomer evaporation during the reaction. On the other hand, PGAs of DPn up to 45 were obtained by the postpolycondensation of a preformed oligomer in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIm(+)Tf(2)N(-)). The precipitation of PGA in reaction medium at long reaction times limited the achievable molar mass. Rate constants were determined for catalyzed and noncatalyzed reactions, assuming a second-order reaction mechanism. The efficiency of esterification catalysts such as Zn(OAc)(2) was low in these media, as only about twofold increases in reaction rate were observed. This was assigned to the preferential interaction of Zn2+ with ionic liquid anion instead of the polymer carboxylic acid end-groups. (c) 2006 Wiley Periodicals, Inc.