Polyamic acid (PAA) nanoparticles were generated by injection of an N-methyl-2-pyrrolidone (NMP) solution containing dissolved PAA into a high-pressure CO2 chamber in which the precipitation of PAA occurred by the antisolvent technique. Supercritical CO2 was then continuously fed into the chamber to dry the precipitated PM. The effects of temperature, pressure and PAA concentration on PM nanopartide morphology and size were systematically examined. The results indicated that PM size could be reduced by decreasing temperature or concentration and by increasing pressure. Spherical PAA nanoparticles with reduced coalescence could be generated at the condition of 313 K, 13.79 MPa and 1.0 wt% PAA in NMP. The resultant PM nanoparticles and the corresponding polyimide (PI) nanoparticles obtained by thermal imidization treatment of PAA at the determined heating conditions were characterized by thermogravimetric analysis and Fourier transform infrared spectroscopy. With evidence of an imide ring structure and high thermal stability, PI was verified to be successfully produced. (C) 2015 Elsevier B.V. All rights reserved.