Superparamagnetic polyimide/γ-Fe2O3 nanocomposite films: Preparation and characterization

Polyimide/γ-Fe2O3 nanocomposite films with superparamagnetic behavior have been prepared by thermal curing of the magnetite (Fe3O4) nanoparticles-containing poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4’-oxydianiline (4,4’-ODA) in N,N-dimethylacetamide (DMAc). To improve the dispersion of the doped nanoparticles, the amine-functionalized Fe3O4 nanoparticles reacted with the PMDA dianhydride in DMAc firstly, and then polymerization was carried out by adding 4,4’-ODA and then PMDA to form the PAA-grafted magnetic particles. Thermal treatment of the Fe3O4-doped precursor film converted the PAA into its final polyimide form with concomitant transformation of Fe3O4 into γ-Fe2O3, yielding a polyimide film with superparamagnetic behavior. The distribution of nanoparticles in the polymer matrix was investigated by transmission electron microscopy and field emission scanning electron microscopy. The nanoparticles and composite films were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, magnetic and mechanical measurement.