Synthesis and properties of pullulan acetate. Thermal properties, biodegradability, and a semi-clear gel formation in organic solvents

Pullulan acetate (AcPL) with various degree of substitution (DS: 1.0-3.0) was synthesized by the reaction of pullulan with acetyl chloride in the presence of pyridine. The product was characterized by gel permeation chromatography (GPC), infra-red (IR) and H-1 NMR spectroscopy. The weight average molecular weights of the products did not decrease less than 190,000 (GPC) in the acetylation reaction. Thermogravimetric analysis (TGA) revealed that AcPL has a higher decomposition temperature (306-363 degrees C) than unmodified pullulan (295 T). Differential scanning calorimetry analysis (DSC) revealed that all the AcPLs exhibit a clear T-g, which decreased with increasing DS value in the range of DS 1.0-2.4. The AcPL with DS 2.4 showed the lowest T-g (153 degrees C), and the AcPL with DS 3.0 had a slightly higher T-g (163 degrees C). Tensile modulus of AcPL films was comparable to that of a popular cellulose acetate film. The biodegration rate of AcPL decreased with increasing degree of acetylation. The AcPL with DS 3.0 was found to form a semi-clear gel in organic solvents such as dimethyl sulfoxide. (DMSO), N,N-dimethylformamide (DMF), and 1,4-dioxane. (C) 2006 Elsevier Ltd. All rights reserved.