Synthesis and thermal studies of heterocyclic siloxanes containing boron

Eight- and six-membered cycloborasiloxanes containing two and one boron atoms respectively are strained ring compounds which undergo ring opening polymerization and ring–ring transformation reactions on thermolysis. Prolonged heating at 200°C results in volatilization of the cyclic boroxine (PhBO)₃, whereas rapid heating of either compound to 1500°C in an inert atmosphere does not result in loss of boron, but affords instead an amorphous residue containing silicon carbide, boron oxide and carbon. Upon further pyrolysis at 1700°C the final product consists of microcrystalline silicon carbide in which are embedded large crystals of boron carbide.