Polysiloxanol condensation and disproportionation in the presence of a superacid |
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Authors: | Agnieszka Grzelka Marek Cypryk Peter C Hupfield |
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Institution: | a Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 ?ód?, Poland b Dow Corning Ltd., Cardiff Road, South Glamorgan, Wales CF63 2YL, UK |
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Abstract: | Kinetics studies of the condensation of model hydroxyl-terminated oligosiloxanes, pentamethyldisiloxane-1-ol (MDH) and heptamethyltrisiloxane-1-ol (MD2H), catalysed by protic complex of tetrakis(pentafluorophenyl)borate in the toluene solution were performed. The dominating reaction was condensation, which was accompanied by disproportionation of oligosiloxanols. Water released in the condensation forms separate dispersed phase, but the phase separation and the presence of water does not affect the rate of the polycondensation. Both processes, condensation and disproportionation, show analogous kinetic laws being first order in silanol and half order in catalyst. They exhibit also similar values of activation parameters. The kinetics are explained by the formation of a reactive protic complex of silanol with borate being in fast preequilibrium with an unreactive complex including two borate molecules and the silanol molecules. The equilibrium lies to the side of the unreactive borate complex. |
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Keywords: | Silanols Polysiloxanes Silanol polycondensation Siloxanol disproportionation Superacid |
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