Solvent-free polymerization of citric acid and D-sorbitol

Copolymers of citric acid and D-sorbitol were synthesized with a solvent-free vacuum-oven synthesis with molar ratios of citric acid to D-sorbitol ranging from 1/1 to 6/1. The extent of the reaction was followed by the monitoring of the residual acid content of the system. As expected, the reaction occurred much more rapidly at 150 than at 110 degrees C. The Fourier transform infrared (FTIR) spectra of the products showed the expected FTIR bands at approximately 1735 and 1188 cm(-1), which were indicative of ester formation. Gel permeation chromatography showed a major product with a molecular weight of approximately 3500 Da. An insoluble material with a water-absorption index of up to 17 was also synthesized and could lead to possible applications as absorbers, thickeners, and biobased seed coatings. Additionally, the mono- and disodium salts of citric acid were also polymerized with D-sorbitol in a manner similar to that of the citric acid system. Soluble polymers were synthesized with a residual acid content of 5 mequiv/g of polymer. These materials showed Ca+2- sequestering ability (up to 0.56 mmol of Ca+2/g of the product). (c) 2006 Wiley Periodicals, Inc.