Hydrolysis kinetics of PMDA/ODA polyimide for monomer recovery using sodium hydroxide in high-temperature water

Monomer recovery from polyimide hydrolysis in high-temperature water was investigated using batch-type reactors with respect to the effects of reaction time, temperature, and sodium hydroxide concentration. Direct observation of the polyimide decomposition in high-temperature water revealed that gas bubbles were produced above 423 K and polyimide dissolution occurred above 573 K. The monomers 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid, PMA) and 4,4ʹ-diaminodiphenyl ether (4,4ʹ-oxydianiline, ODA) were produced in the early stages of the reaction. The generated PMA decomposed to form carbon dioxide after a reaction time of 10 min at 573 K, while the ODA was relatively stable. Moderate temperature and sodium hydroxide concentration promoted polyimide hydrolysis, whereas overcracking of the polyimide occurred in the presence of excess sodium hydroxide at high temperature. A reaction time of 5 min and alkali concentration of 22 mmol/kg were found to be the optimal conditions for monomer recovery at 573 K.