Organosilicon polymers Molecular weight

The thermal stability of composites is mainly determined by the thermal stability of the polymer support. High-molecular-weight organosilicon compounds are the largest group of thermally stable polymers. 

Furthermore, the molecular weights of silicone polymers are higher than their viscosities indicate. This is a function of the low intermolecular forces characteristic of organosilicones. 

An argon ionisation detector to the gas-liquid chromatography of organosilicon compounds452 was unsuitable for the analysis of methylchlorosilanes. However, a pyrolysis chamber permitted the analysis of both linear and cross-linked methylsiloxane polymers of high molecular weight. 

The commercially produced continuous and multifilament Nicalon (Hercules) fiber is produced from polydimethylsilane however other organosilicon polymers have been used for the production of silicon carbide fiber. Polydimethylsilane is first distilled to remove the low molecular weight components, and polymer of average molecular weight 1500 is melt spun at 280°C and cured in air at 200°C. The fiber is then heat treated between 800 and 1500°C in nitrogen or vacuum. Optimum mechanical properties are achieved at ca 1250°C. Listed properties of the Nicalon fiber are modulus 200 GPa and tensile strength 2.8 GPa (1). 

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