Low temperature solventless silicone resins

Abstract

Organosilicon resins having excellent thermal shock resistance in either the filled or unfilled state are obtained by curing mixtures of (A) a copolymer of (in mole percent) 35 to 42 monophenylsiloxane, 0 to 12 diphenylsiloxane, 35 to 50 dimethylsiloxane and 8 to 15 vinylmethylsiloxane with (B) a copolymer of (in mole percent) 8 to 15 diphenylsiloxane, 30 to 55 methylhydrogensiloxane, 28 to 45 dimethylsiloxane and 5 to 12 trimethylsiloxane in amount such that there is a stoichiometric amount of SiH and Si vinyl ± 10 percent of either ingredient. The preferred fillers are mixtures of 1/32 to 1/8 inch glass fibers and 2 to 8 microns crystalline silica.

That which is claimed is: 
     
       1. A curable composition consisting essentially of a mixture of A. a copolymer of (in mole percent) 35 to 42 monophenylsiloxane, 0 to 12 diphenylsiloxane, 35 to 50 dimethylsiloxane and 8 to 15 vinylmethylsiloxane, and   B. a copolymer of (in mole percent) 8 to 15 diphenylsiloxane, 30 to 55 methylhydrogensiloxane, 28 to 45 dimethylsiloxane and 5 to 12 trimethylsiloxane in amount such that there is a stoichiometric amount of SiH and Si vinyl ±10 percent of either ingredient.   
     
     
       2. The cured composition of claim 1 in which a platinum catalyst is used as the curing agent. 
     
     
       3. A curable composition consisting essentially of, in percent by weight, 35 to 65 of (A) plus (B) of claim 1, 5 to 25 of glass fibers having an average length of from 1/32 to 1/8 inch and 10 to 50 of crystalline silica having an average particle size of 2 to 8 microns. 
     
     
       4. The composition of claim 3 which has been cured with a platinum catalyst. 
     
     
       5. A curable composition consisting essentially of, in percent by weight, 45 to 55 of (A) plus (B) of claim 1, 10 to 15 of 1/32 to 1/8 inch glass fibers and 30 to 45 of a crystalline silica having an average particle size of 2 to 8 microns. 
     
     
       6. The composition of claim 3 in which the glass fibers are 1/16 inch and the silica filler has an average particle size of 2 to 5 microns. 
     
     
       7. The composition of claim 5 in which the glass fibers have an average length of 1/16 inch and the silica has an average particle size of 2 to 5 microns. 
     
     
       8. The cured composition of claim 5. 
     
     
       9. The cured composition of claim 6. 
     
     
       10. The cured composition of claim 7.