Fabrication of Unique Porous Polyimide Nanoparticles Using a Reprecipitation Method

Porous polyimide (PI) nanoparticles were fabricated using the reprecipitation method, with a second polymer as a porogen, and subsequent imidization. Poly(acrylic acid) was a suitable porogen for generating unprecedented PI nanoparticles having superficial nanopores, the sizes of which were in the range 20−70 nm. The porous morphology of the PI nanoparticles was affected mainly by the molecular weight and content of poly(acrylic acid). After thermal imidization, almost no poly(acrylic acid) remained inside the porous PI nanoparticles. Infrared spectroscopy and thermogravimetric analysis indicated that the porous nanoparticles consisted purely of PI and exhibited high thermal stability (5% weight loss temperature: 400 °C). The porous structure probably resulted from microphase separation of poly(amic acid) and poly(acrylic acid) during the reprecipitation process. This strategy provides a new means for improving the degree of porosity of PI nanoparticles, which have the potential for application as alternative materials for preparing interlayer dielectrics.