A bifunctional terminal organic-inorganic dendrimer with fluorocarbon and hydrocarbon units at its terminal groups was successfully prepared by a hydrosilylation reaction, and a combination of a ring-opening reaction and condensation reaction of octakis(propenylsuccinicanhydrido)polyhedraloctasilicate (OS-SA) with 1-decanol and 1H,1H,2H,2H-perfluoro-1-decanol. The structure of the OS-core dendrimer bearing the decyl and 1H,1H,2H,2H-heptadecafluorodecyl groups (OS-CF) was fully characterized by FT-IR, NMR spectra, and MALDI TOF MS spectrum. The crystallinity of the fluorinated domains in OS-CF decreased in comparison with that in I-CF and the fluorocarbon/hydrocarbon chains form no ordered structure due to suppression of the molecular motion of their branches resulting from the rigid inorganic core. The composite films of PMMA containing OS-CF were prepared through solution blending of PMMA with various concentrations of OS-CF (5, 10, and 20 wt %). The refractive index of the neat PMMA film is 1.49, and the refractive indices of the composite films containing OS-CF decrease linearly with increases in the OS-CF weight fraction. (c) 2017 Wiley Periodicals, Inc.