Synthesis and properties of etherified pullulans

Propyl- and butyl-etherified pullulans (PrPL and BuPL) with various degree of substitution (DS: 1.02–2.61) were synthesized by the reactions of pullulan with 1-bromopropane and 1-bromobutane in the presence of sodium hydroxide, respectively. The structure of PrPL and BuPL was characterized by gel permeation chromatography, IR and 1H-NMR spectroscopy. The alkylpullulans were water resistant and had good solubility in general organic solvents. Both PrPL and BuPL showed a clear glass transition temperature (Tg: 73–141 °C), which decreased with increasing DS. The PrPL and BuPL with DS 2.45 and 2.61 showed Tg at 78 and 73 °C, and 5% weight loss temperature (Td) at 273 and 268 °C, respectively, indicating that these alkylpullulans have a sufficient processing window in melt processing.