The overall synthesis was carried out at ambient temperature. Chitosan (medium molecular weight, 5.00 g, equivalent to 31.0 mmol glucosamine) was dissolved in aqueous HCl (250 mL, 0.37% v/v) by vigorous stirring using mechanical stirrer (Eurostar, IKA, Germany) over 3 hrs. In separate flasks, DIC (2.03 or 5.91 g equivalent to 16.10 or 46.80 mmol, respectively) was added to magnetically stirred lactic acid (1.44 or 4.20 g equivalent to 16 or 46.80 mmol, respectively) aqueous solutions (200 mL). Fifteen minutes later, HOBt (2.10 or 6.28 g equivalent to 15.5 or 46.50 mmol, respectively) was added to corresponding DIC-lactic acid reaction mixtures and further stirred for 2 hrs. Thereafter, the DIC-activated lactate solutions were transferred to chitosan solutions and left over 24 hr under stirring. The reactions were
terminated by adding acetone (3×200 mL) to precipitate the polymers. The resulting precipitates were washed thoroughly with ethanol (3×300 mL) to remove the DIC urea byproduct, followed by (3×300 mL) acetone to washout water and ethanol. Finally, the resulting masses were left overnight under fume hood to dry, and then desiccated to give
chitosan lactate 0.5 equivalent (CL0.5) and chitosan lactate 1.5 equivalent (CL1.5), respectively.