Synthesis, characterization and magnetic properties of novel heat resistant polyimide nanocomposites derived from 14H-dibenzo [a,j] xanthene

New magnetic and heat resistant polyimide (PI) nanocomposites containing two different types of magnetic nanoparticles were successfully prepared by a solution intercalation technique. New PI derived from 14H-dibenzo [a,j] xanthene, which contain benzophenone, amide and ether moieties, was synthesized by thermal cyclization of an aromatic precursor polymer, obtained from the reaction of the new diamine N-(4-(4-(14H-dibenzo [a,j] xanthen-14-yl) phenoxy) phenyl)-3,5-diaminobenzamide and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA). The synthesized PI was characterized by Fourier-transform infrared (FTIR), nuclear magnetic resonance (H-1 NMR), UV-vis and photoluminescence (PL) spectroscopy. The structural and electronic properties of the xanthene-based polyimide unit were studied by ab intio DFT method using the B3LYP/6-31G (d) level of theory. The HOMO, LUMO and band gap (Delta E = ELUMO - EHOMO) energies of the polyimide unit were calculated. PI nanocomposites were prepared by coating magnetite (Fe3O4) nanoparticles sequentially with silica (SiO2) and 1-methyl-3-(triethoxysilylpropyl) imidazolium chloride; the Fe3O4 and surface-modified Fe3O4 (Fe3O4@SiO2-ImCl) nanoparticles were then dispersed in the poly (amic acid) solutions and thermally imidized to form PI/Fe3O4 and PI/Fe3O4@SiO2-ImCl nanocomposites. The morphology, crystalline phase, thermal stability and magnetization properties of the resultant materials were characterized by field emission scanning electron microscopy (FE-SEM) transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM) and FTIR techniques. The results indicated that the as-prepared nanocomposites exhibited superparamagnetic properties and improvements in the thermal stability compared to neat polyimide. Furthermore, the Fe3O4@SiO2-ImCl nanoparticles has better dispersion in the polymer matrix, than the uncoated Fe3O4 nanoparticles, and thus the PI/Fe3O4@SiO2-ImCl nanocomposite prepared using the coated nanoparticles exhibits a better intercalated morphology and improved thermal properties than the PI/Fe3O4 nanocomposite.