Pyrolytic conversion of organopolysiloxanes

•TG/MS analysis provides an excellent analytical support for valuable information.•The chronology of events of the thermal degradation of organopolysiloxanes has been established.•Divinylbenzene enables one to achieve desirable characteristics and controllable carbon contents.•Raman mapping provides information on densities of defects in turbostratic carbon.

This study extends previous work on in-situ generation of nanographene domains in silicon oxycarbide polymer-derived ceramic nanocomposites. The thermal conversion of cross-linked polyhydridomethylsiloxanes (PHMS) has been studied as a function of its initial organic structure and its content. Two cross-linking additives containing vinyl groups, tetramethyl-tetravinyl cyclotetrasiloxane (TMTVS) and divinylbenzene (DVB), have been reacted with the SiH groups of the PHMS via Pt catalyzed hydrosilylation. These polymers gave a high ceramic yield of 78-85 wt% upon pyrolysis at 1000 °C-1400 °C in inert atmosphere. The use of the aromatic cross-linker (DVB) induces significantly higher carbon content in a controlled fashion into the derived ceramics compared with the TMTVS. The chemistry involved in the in-situ evolution of low-dimensional graphene architectures embedded into silicon oxycarbide network has been studied in detail using thermal gravimetric, mass spectroscopy analyses (TG-MS) and Raman spectroscopy. The presence of aromatic functional groups (DVB) at the polymeric stage leads to graphene generation at lower temperatures than in the case of TMTVS cross-linker. Raman spectroscopy analysis of DVB cross-linked PHMS showed evidence of the beginning of formation of free sp2 carbon domains from 800 °C. Raman mapping allows obtaining the chemical and the structural distribution of the resulting phases.

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