Dehydrocoupling of tris(hydridosilylethyl)boranes with ammonia or amines: a novel route to Si-B-C-N preceramic polymers

The synthesis of boron-modified polysilazanes of general type {B[C2H4Si(R)- NR '](3)}(n) [R= CH3, (NR ')(0.5); R ' = H, CH3] by dehydrogenative couplin g of tris(hydridosilylethyl)boranes B[C2H4Si(CH3)nH(3-n)](3) (C2H4 = CHCH3, CH2CH2; n = 0, 1) and ammonia or methylamine is reported. Detailed charact erization of the title compounds was performed using spectroscopic methods such as solid-state NMR spectroscopy, IR spectroscopy, and elemental analys is. Thermolysis produces amorphous Si-B-C-N ceramics with ceramic yields be tween 25 and 83%, as determined by thermogravimetric analysis (TGA) in argo n. High-temperature TGA in an argon atmosphere reveals that a number of the ceramics obtained resist degradation up to similar to 2000 degreesC. X-ray diffraction studies of the as-obtained amorphous materials show formation of alpha -SiC or alpha -SiC/beta -Si3N4 crystalline phases between 1600 and 1800 degreesC, depending on the composition of the materials. Copyright (C ) 2001 John Wiley & Sons, Ltd.