Polymer–ceramic conversion of a highly branched liquid polycarbosilane for SiC-based ceramics

Liquid polycarbosilane (LPCS) with a highly branched structure was characterized by fourier-transform infrared spectrometry (FT-IR) and 1H, 13C, 29Si nuclear magnetic resonance spectrometry (NMR). The LPCS was then cured and pyrolysized up to 1,600 C under flowing argon. The structural evolution process was studied by thermogravimetric analysis and differential scanning calorimetry (TG-DSC), FT-IR, and X-ray diffraction (XRD). Hydrosilylation, dehydrocoupling, and polymerization cross-linking reactions between Si–H and C=C groups occurred at low temperatures, which mainly accounted for the high ceramic yield (70%) up to 1,400 C. The organic groups gradually decomposed and the structure rearranged at high temperatures. The FT-IR analysis revealed that Si– CH2–Si chains, the backbone of original polymer, can be retained up to 1,200 C. At temperatures higher than 1,200 C, the Si–CH2–Si chains broke down and crystalline SiC began to form. The final crystalline products were b-SiC and a small amount of carbon.