Novel Sulfur-Containing Cross-Linking Agent for Si-Based Preceramic Polymers

Cross-linking polymethylhydrosiloxane (PMHS) with divinylthiophene (DVT) via hydrosilylation in highly dilute conditions and subsequent supercritical drying in CO2 yield a polymeric aerogel containing aromatic sulfur integrally and uniformly distributed throughout the monolith. Fourier-transform infrared (FT-IR) spectroscopy indicates almost complete consumption of vinyl groups and Si-H bonds in the product. Both FT-IR and Raman spectroscopic analyses support loss of conjugation of vinyl groups with the retained double bonds of the thiophene ring. Scanning electron microscopy (SEM) indicates a condensed colloidal structure with characteristic particulate diameters of about 165 nm. SEM coupled with energy dispersive X-ray spectroscopy elemental mapping shows that sulfur is distributed homogeneously in the polymeric aerogel. Porosimetry of the mesoporous aerogel indicates the effective average pore diameters are about 12 nm. Thermogravimetric analysis (TGA) establishes greater thermal stability of the PMHS-DVT product than either of the pure unreacted components. TGA coupled with mass spectrometric (TG-MS) identification of the volatiles released during pyrolysis shows that sulfur is driven from the cross-linked polymer as thiophene and its derivatives. Recorded mass spectra support the hypothesis that cross-linking DVT bridges between PMHS chains in the polymeric aerogel, and that this results in a more thermally stable monolith.