To obtain a material which has light gray color, can be heat foamed to provide a heat-resistant elastomer as a sealing slag by incorporating a nonreinforcing filler, which is thermally stable up to 1,200°C, such as SiO2, and a boron compd. into a specified organopolysiloxane.
An organopolysiloxane having a condensable terminal represented by formula I (wherein R represents a 1-18C hydrocarbon; x represents hydroxyl; and n≥10 is advantageously used as a condensation crosslinkable material, and an organosiloxane represented by formula II (wherein R' represents a 1-18C hydrocarbon; Y represents a hydrocarbon having an aliph. carbon-carbon multiple bond; a is O or 1; b is 20 to 10,000; and c is 0 or 1 to 300) is advantageously used as an addition crosslinkable material. The crosslinking catalyst may be a conventional one, such as a Ti or Pt compd. The boron compd. is selected from metal borides, such as boron carbide and zinc boride. Diatomaceous earth, quartz, barium sulfate, mica or the like, which is thermally stable up to 1,200°C, is used as the nonreinforcing material in an amt. of not less than 75wt%. The resultant compsn. has light gray color and, when exposed to heat of combustion, can produce a slag foam and, in addition, can maintain air tightness to prevent spreading of combustion.
KURZ ALFRED
BALK GERHARD
