Selective acetylation of amorphous region of poly(vinyl alcohol) in supercritical carbon dioxide

The postfunctionalization of poly(vinyl alcohol) (PVA) with a hierarchical structure has been challenging because conventional polymer functionalization reactions are performed in homogeneous solution states. In this study, the selective functionalization of PVA was achieved in supercritical carbon dioxide (sc-CO2) through acetylation in the amorphous region only and not in the crystalline region. The crystalline region of PVA was retained in the amorphous-selective acetylated PVA synthesized insc-CO2. In addition, the oriented structure of the PVA crystallites was maintained even after acetylation of the drawn PVA film in sc-CO2. Moisture adsorption affected the crystalline structure of PVA acetylated in sc-CO2. The acetylated PVA synthesized in sc-CO2 included a larger number of water molecules under humid conditions, and the increase in thickness was smaller than that of randomly acetylated PVA. This reason was the rigid crystalline structure and the sequential hydrophilic PVA units in the PVA acetylated in sc-CO2.