Polyborosilazane

Riedel et al. and Kienzle published the synthesis of a polyborosilazane by ammonolysis of tris(dichloromethylsilyl-ethylene)borane, B(C2H4Si(CH3)Cl2)3... 

Accordingly, vinylchlorosilanes were initially treated with ammonia and the obtained polyvinylsilazanes [(H2C=CH)SiRNH] were subsequently reacted with Me2S BH3 to give the corresponding polyborosilazanes with a yield of 100%. Purification was performed by removing the solvent and by-product dimethlyl-sulfane in a high vacuum. 

SCHEME 18.31 Synthesis of polyborosilazanes through thermal induced hydrosilylation of oligovinylsilazane and tris(hydridosilylethyl)boranes (schematic representation). 

Aluminum nitride polymer Hybrid co-polymers Polyborosilazanes Polycarboxilane modified with At... 

Keywords Hydroboration of Vinylchlorosilanes / Preceramic Polymers / Polyborosilazane / Thermal Stability / Synthesis... 

Another route to polyborosilazanes, suitable for the synthesis of ceramics in the Si/B/N system, consists of an adaptation of the well-known oxo-sol-gel process to the ammonia system. Metal alkoxides are replaced by metal alkylamides, and ammonia instead of water serves as the solvolysing agent. 

In ceramics from polyborosilazanes, on the other hand, ordering effects are demonstrated only at 1700°C and strong crystallization at 1800°C [171]. The crystallization of Si3N4 at T > 1750°C in this system was also confirmed by Baldus et al. [172] who reported even higher crystallization temperatures, sometimes exceeding 1900°C. 

UBE Chemicals synthesized amorphous Si-Ti-C-O fibers from the PCS-titanium alkoxide compound polymer. These so called Tyranno fibers show excellent properties and can be spun thinner than the Nicalon fibers (see Table 4). However heating above 1000°C results in a crystallization of the fiber. In the mid 1990s the German company Bayer AG synthesized an amorphous Si-B-N-C fiber, by pyrolysis of a polyborosilazane polymer [56]. This SiBN3C fiber (see Fig. 11) has a tensile strength of 3 GPa and maintains its amorphous character up to 1800°C. The advantage of the production route from liquid to solid to produce SiC has also attracted attention for... 

Chu and co-workers [8] have discussed the thermal properties of polyborosilazanes produced by exposure of hexamethyl cyclotrisilazone (HMCTS) to boron trichloride. 

Perhydropolysilazane + B(OME)3 polyborosilazane(PBSZ). Composition is for polymer after being heated at 500 °C. 

Polyborosilazanes (PBSZs) are produced by reaction of PHPSZ with trImethyl borate (Si/B = 3) In pyridine. The solution Is heated for 3 hours at 120 C. After cooling, o-xylene Is added and the solvent Is removed by vacuum distillation at 50 C, yielding a white PBSZ powder (Mn = 2100-2200) that Is soluble in toluene and chloroform but does not melt < 500 C [16]. The PBSZ composition Is close to SiB0.3eO0.3tN1.0eC0.31H3.94. 

Chu and co-workers [41] carried out pyrolysis of the refractory polymer polyborosilazane under nitrogen at temperatures between 1250 and 1800 °C. The boron content of the pyrolysis product increased with increased thermal exposure... 

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