Production of polyamic acid in supercritical carbon dioxide with N,N-dimethylformamide.

ABSTRACT To develop a microscale processing technique for aromatic polyimides (APIs) in supercritical carbon dioxide (scCO₂), the relationships between the polymerization condition, the phase behavior during polymerization and the molecular weight of polyamic acid (PAA)-an intermediate in the production of polyimides-were investigated in scCO₂ at 50°C. 4,4′-Diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) were used as monomers of aromatic diamine and tetracarboxylic dianhydride, respectively, and 19 mol % of N,N-Dimethylformamide (DMF) was added to scCO₂ as a cosolvent. The cloudy phase appeared immediately when ODA and PMDA were mixed under any experimental conditions. However, the appearances of the phase behaviors during polymerization differed depending on the polymerization pressure and the initial monomer concentration. The number average molecular weight of PAA increased as the monomer concentration was increased in scCO₂, as was the case with polymerization in pure DMF at atmospheric pressure, despite differences in the phase behavior. On the other hand, the weight average molecular weight of PAA depended on the phase behaviors during polymerization along with the monomer concentration. Moreover, API obtained from the PAA synthesized in scCO₂ was analyzed using a Fourier transform infrared spectrophotometer and thermogravimetric analyzer, and the results were compared with those of APIs obtained by the solution polymerization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39878. [ABSTRACT FROM AUTHOR]