KINETICS AND MECHANISM OF OLIGOSILOXANOL CONDENSATION AND OLIGOSILOXANE REARRANGEMENT CATALYZED WITH MODEL PHOSPHONITRILE CHLORIDE CATALYSTS

The condensation kinetics of 1,1,3,3,3-pentamethyldisiloxanol (MDH) in n-heptane solution were compared for two types of phosphonitrilic cat alyst, hexachloro-1 lambda-diphosphaza-1-enium hexachloroantimonate sa lt, [Cl3PNPCl3](+) [SbCl6](-), 1, and P-trichloro-N-dichlorophosphoryl e phosphazene, [Cl3PNP(O)Cl-2], 2. The kinetic law of reaction is not changed when 1 is replaced by 2. The process is selective leading to l inear decamethyltetrasiloxane (MD2M, where D denotes the dimethylsilox ane unit, and M denotes the trimethylsiloxane unit) as almost the excl usive primary product. Other oligomers of the MDnM series are formed a s a result of the MD2M rearrangement. The MD2M rearrangement was studi ed in separate experiments in the absence of the siloxanol and water. Both catalysts 1 and 2 gave similar rate-concentration behaviour. Some of the kinetic features of the process resemble those of chain reacti ons and mechanisms of the MDH condensation, and the MD2M rearrangement are discussed.