High char yield novolac modified by Si-B-N-C precursor: Thermal stability and structural evolution

In this contribution, novolac modified by CSEB ceramic precursor (B,B,B-tris[(chlorodimethylsilyl)-ethane]borazine, CSEB) was synthesized successfully. The corresponding molecular structure, chemical state and thermal property were characterized by FT-IR, Raman spectra, XPS, NMR and TGA. Meanwhile, DTA/TG/MS test was also performed to track the weight loss and gas evolution of modified novolac during the thermal degradation. CSEB could obviously improve the thermal decomposition temperature and the char yield of novolac. The maximum decomposition rate temperature is increased up to 575.2 °C. The char yield is increased to 75.5% at 800 °C, 72.6% at 1000 °C and 68.7% at 1200 °C, respectively. The improvement of the thermal stability of modified novolac could be mainly attributed to the incorporation of six-membered borazine ring (B₃N₃), elements of Si, B and N. The B₃N₃ ring remains stable at 1400 °C. And fixed structure Si-O_x was formed during heat treatment. Moreover, CSEB also promote the graphitization.