Sonochemical synthesis of a poly(methylsilane), a precursor for near-stoichiometric SiC

We report a sonochemical process for a single-pot synthesis of high molecular weight poly(methylsilane) (PMS) of composition [(CH3SiH)(x)(CH3Si)(y)(CH3Si2)(z)](n), where x + y + z = 1 and 0.65 greater than or equal to (x + z) greater than or equal to 0.23 by the sodium polycondensation reaction of CH3SiHCl2 in a solvent mixture of hexane or toluene and tetrahydrofuran (THF) using ultrasonic activation (47 kHz, 130 W). This polycondensation reaction takes place in two stages: (1) 10-25 h of reaction in which an oligo(methylsilane) (OMS) oil (0.91 greater than or equal to (x + z) greater than or equal to 0.83) is obtained that gives low ceramic residue yields of silicon-rich SiC on pyrolysis in argon and (2) 25-40 h of reaction during which is obtained a PMS solid that gives high ceramic residue yields of near stoichiometric SiC on pyrolysis. PMS also may be prepared by branching of the oligo(methylsilane) with sodium and ultrasonication for similar to 5 h in a toluene and THF solvent mixture. PMS is soluble in hexane and toluene and its pyrolysis in n gives a ceramic residue yield up to 90%. In addition to the main product of the condensation reaction, a high molecular weight PMS may be extracted from large NaCl crystals (the other product of the CH3SiHCl2/Na reaction). A comparison of sonochemical and conventional (reflux) activation also is provided. Ceramic fibers, films, and solid monoliths were prepared from PMS without requiring a curing step.