A novel molybdenum-containing polycarbosilane, polymolybdenocarbosilane (PMoCS), for SiC(Mo) fiber has been synthesized from polysilacarbosilane (PSCS) and MoCl5 as raw materials. The synthesis conditions is investigated. Characterization performed on the as-synthesized PMoCS includes Fourier Transformed Infrared Spectroscopy (FT IR), gel-permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), 1H NMR, and 29Si NMR, respectively. The polymer-to-ceramic conversion is studied with thermogravimetric analysis (TGA) and X-ray diffraction (XRD). Preliminary research on the melt spinnability of PMoCS is carried out. The results show that the synthesis reaction is temperature-dependent. Mo exists mainly as SiMo bonds. The reaction mechanism is believed to involve HCl elimination between SiH and MoCl, and followed by the Kumada rearrangement. The ceramic yield of PMoCS, prepared with 10 wt % MoCl5, is approximately 78.5% at 1200 degrees C in a N2 flow. The XRD results suggest that ceramics pyrolyzed in the range of 8001000 degrees C are all amorphous, while -SiC and -MoSi2 crystals are observed at 1200 and 1400 degrees C, respectively. The conversion from -MoSi2 to -MoSi2 is almost completed at 1600 degrees C. PMoCS is melt spinnable into flexible and uniform green fibers with the diametersabout 13.4 m to 12.2 m. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013