Abstract
The condensation kinetics of 1,1,3,3,3-pentamethyldisiloxanol (MDH) in n-heptane solution were compared for two types of phosphonitrilic catalyst, hexachloro-1 λ-diphosphaza-l-enium hexachloroantimonate salt, [Cl 3PNPCl 3] +[SbCl 6] −, 1, and P-trichloro- N-dichlorophosphoryle phosphazene, [Cl 3PNP(O)Cl 2], 2. The kinetic law of reaction is not changed when 1 is replaced by 2. The process is selective leading to linear decamethyltetrasiloxane (MD 2M, where D denotes the dimethylsiloxane unit, and M denotes the trimethylsiloxane unit) as almost the exclusive primary product. Other oligomers of the MD n M series are formed as a result of the MD 2M rearrangement. The MD 2M rearrangement was studied 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 reactions and mechanisms of the MDH condensation, and the MD 2M rearrangement are discussed.
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