Chemistry, structure, and thermodynamic stabilization of SiOC polymer derived ceramics made from commercial precursors

This study explores the energetics and structure of polymer derived ceramics (PDCs) derived from the pyrolysis of preceramic polymers: SPR-212 (SPR), polyhydromethylsiloxane (PHMS) blend, and 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (TTCS) at 1200 and 1500 oC. There are close similarities in the composition of PDCs derived from PHMS (blend) and SPR-212 at 1200 oC, but high-resolution X-ray photoelectron spectroscopy shows notable differences in their microstructure. Enthalpies of formation (ΔHºf,elem) of SPR-1200, TTCS-1200, PHMS-1200, SPR-1500, TTCS-1500, and PHMS-1500 are -154.40 ± 3.19, -116.35 ± 3.48, -197.55 ± 3.05, -170.12 ± 3.50, -167.29 ± 3.35, and -212.43 ± 2.71 kJ mol-1, respectively. PDCs derived from low-cost commercial precursors (PHMS blend) appear to be more thermodynamically stable than those derived from an industrial preceramic polymer (SPR-212). Thermodynamic stability of the SiOCs increases with pyrolysis temperature. The results suggest that differences in silicon mixed bonding environments and their relative amounts (SiO3C, SiO2C2, or SiOC3) lead to differences in thermodynamic stabilization.