Fabrication of highly refractive BaTiO3 nanocomposite films using heat resistant polymer as matrix

[Display omitted] •Heat-resistant nanocomposite films with high refractive indices.•In situ polymerization to disperse refractive nanoparticles into polyimide films.•A combination of thermal and chemical imidizations to enhance refractive index. Highly refractive, heat-resistant BaTiO3 nanocomposite films were fabricated via in situ polymerization to homogeneously disperse barium titanate (BT) nanoparticles into polyimide (PI) matrix. BT nanoparticles surface-modified with O-phosphorylethanol phthalimide (PPHI) were employed to the in situ polymerization in which condensation reactions of a diphthalic anhydride and a diamine were conducted to form the prepolymer of poly(amic acid) (PAA) that was thermally imidized in the following step. The nanoparticles surface-modified were added to PAA solution at different times in the polymerization to examine the effect of PAA molecular weight on the refractive index (RI) of the nanocomposite films, which indicated that relatively low molecular weights (