Synthesis and characterization of alginic acid ester derivatives

Esters derivatives of alginic acid (Alg) were prepared in carboxylic acid/carboxylic acid anhydrides system by using aqueous perchloric acid as the catalyst. Degree of substitution of hydroxyl group of Alg was estimated to be 2, showing that the hydroxyl group of Alg was fully esterified. Alg acid esters showed the solubility to common organic solvents such as acetone and chloroform. In particular, alginic acid hexanoate formed self-standing solvent-cast film, although the film showed brittle mechanical behavior. Furthermore, Alg esters showed glass transition temperature (T_g) in a temperature range between 100 and 200°C, that is in the same range as the conventional synthetic amorphous polymers. It was also shown that the T_g gradually lowered with the increasing acyl side chain length. These results show that Alg esters are plastic materials with tunable organosolubility and thermal properties.