Jean De La Croi Habimana

KINETICS AND MECHANISM OF THE REACTION BETWEEN OLIGOSILOXANES AND P-TRICHLORO-N-DICHLOROPHOSPHORYL MONOPHOSPHAZENE (Cl3P[dbnd]N-POCl2)

Abstract 31P NMR investigation has been made of the action of Cl3P˭N-POCl2(I) first on hexamethyldisiloxane (Me3Si)2O and then on oligosiloxanes Me3Si-(OSiMe2)n-OSiMe3 n = 2 and n=3. The reactions were carried out in bulk or in solution with molar ratios siloxane/(I) varying from I to 5. It was demonstrated that only the monosubstitution of a chlorine atom by the -(OSiMe2)n,-OSiMe3 species n = 0, 2, 3 with elimination of trimethylchlorosilane occurred leading to the derivatives Cl2OP-N˭PCl2O(SiMe2-O)nSiMe3 (II). For n=2, 3 the siloxane redistribution reactions were observed by 29Si NMR analysis. A two steps mechanism is proposed. consisting in a nucleophilic substitution, involving a tricoordinate phosphazenium intermediate, followed by the formation of an active ionic centre probably an oxonium ion, arising from the solvatation by the siloxane of this phosphazeniurn ion and /or of (II) leading to the redistribution reactions. The influences of the solvent, of trimethylchlorosilane, of the temperature, and of the addition of a protonated species (MDH) were investigated.

CYCLIC PHOSPHONITRILIC COMPOUNDS BEARING ─N═PCl3 GROUP AS HOMOGENOUS CATALYST TOWARDS THE SILANOL CONDENSATION

Condensation reactions of 1,1,3,3,3 pentamethyldisiloxane-ol (MDH), in toluene catalysed by two[9.5pc] types of phosphonitrilic catalyst bearing a phosphazene ─N═PCl3, were studied using sampling and gas chromatographic analysis method. The condensation kinetics reactions were compared for both phosphazene compounds. The process is selective, leading to linear decamethyltetrasiloxane MD2M, (where D denotes the dimethylsiloxane unit and M denotes the trimethyloxysilane unit) as almost the exclusive primary product. The mechanisms of the MDH condensation are discussed using the 31 P NMR sampling technique.