Preparation of poly(amic acid) nanoparticles using the reprecipitation method and their imidization

We have successfully fabricated polyimide (PI) nanoparticles through chemical imidization of poly(amic acid) (PAA) precursor nanoparticles, which were prepared by the reprecipitation method. PAA used as a precursor polymer was produced by polyaddition of 4,4′-oxydianiline and 4,4′ -(2,2-hexafluoroisopropylidene) diphthalic anhydride in N-methyl-2-pyrrolidinone. Chemical imidization of PAA nanoparticle was performed by adding a small amount of pyridine/acetic anhydride mixture (1:1) into the PAA nanoparticle dispersion. Almost quantitative conversion from PAA to PI was confirmed by IR spectra. According to SEM observations, both PAA and the corresponding PI nanoparticles were spherical. The particle size distribution was found by DLS measurements to be unchanged before and after the chemical imidization.