Synthesis, Characterization, and Properties of Silylene-Acetylene Preceramic Polymers

A series of silylene-acetylene preceramic polymers 3a-e were synthesized by polycondensation reaction of dilithioacetylene with dichlorosilane (H2Si2Cl2) or/and methyldichlorosilane (MeSiHCl2). Their structures were confirmed by infrared spectra (IR), and H-1 and Si-29 NMR spectroscopies. Differential scanning calorimetry (DSC) diagrams show exotherms centered at 200 to 233 degrees C temperature range, attributed to crosslinking reaction of the acetylene and Si-H groups. After thermal treatment, the obtained thermosets 4a-e possess excellent thermal stability. Thermogravimetric analysis (TGA) under nitrogen show the T(d5)s (temperature of 5% weight loss) for all the thermosets are above 600 degrees C, and the overall char yields are between 95.62% and 89.67% at 900 degrees C. After pyrolysis at 1200 degrees C, the obtained ceramic residues 5a-e exhibit good thermo-oxidative stability with final weight retention between 98.76% and 91.66% at 900 degrees C under air. In particular, perhydroploy(silylene)ethynylene 3a, which has the highest Si/C ratio in silylene-acetylene polymers, has the highest char yield, and the derived ceramic material 5a displays the best thermo-oxidative stability. Based on Scanning electron microscopy and its associated energy-dispersive X-ray microanalysis (SEM EDX) and C-13 magic angle spinning nuclear magnetic resonance (MAS NMR) analysis, ceramic 5a contains the highest SiC content. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 4064-4070, 2008