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چکیده
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New magnetic and heat resistant polyimide (PI) nanocomposites containing two different types of magnetic nanoparticles were successfully prepared by a solution inter-calation technique. New PI derived from 14H-dibenzo [a,j] xanthene, which contain benzophenone, amide and ether moi-eties, was synthesized by thermal cyclization of an aromatic precursor polymer, obtained from the reaction of the new diamineN-(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), nu-clear magnetic resonance ( 1 HNMR),UV-visand 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 (ΔE = 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 magneti-zation 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 indi-cated that the as-prepared nanocomposites exhibited superparamagnetic properties and improvements in the ther-mal stability compared to neat polyimide. Furthermore, the Fe3O4@SiO2-ImCl nanoparticles has better dispersion in the polymer matrix, than the uncoated Fe3O4nanoparticles, and thus the PI/Fe3O4@SiO
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