Syntheses and Properties of Sila-Functional Oligosiloxanes-Linear and Cyclic Tetrasiloxanes with Methyl and Vinyl Groups-

The syntheses of the titled oligosiloxanes by controlled hydrolysis of the corresponding isocyanatosilanes under vapor phase or in THF (or THF/ether) were investigated. The vapor phase hydrolysis of RSi(NCO)3 (R = Me, Vinyl) with a water-1,4-dioxane vapor gave the disiloxanes [R(OCN)2Si]2O in yields of 85% (R = Me) and 90% (R = Vinyl). Further vapor phase hydrolysis of the disiloxanes provided the linear tetrasiloxanes NCO[SiR(NCO)O]3SiR(NCO)2 in yields of 71% (R = Me) and 69% (R = Vinyl). The cyclotetrasiloxanes [R(OCN)SiO]4 were synthesized in yields of 12% (R = Me) and 33% (R = Vinyl) or 24% (R = Me) and 58% (R = Vinyl) by hydrolysis of the disiloxanes or of the linear tetrasiloxanes in THF, respectively. On the other hand, the linear tetrasiloxanes OCN[SiR(OPri)O] 3SiR(OPri)(NCO) were obtained in yields of 50% (R = Me) and 56% (R = Vinyl) by hydrolysis of [R(OCN)(PriO)Si]2O prepared from RSi(OPri)(NCO)2 under mild conditions in THF/ether, while the cyclic tetrasiloxanes [R(PriO)SiO]4 were afforded in the yield of 61-62% by hydrolysis of the disiloxanes under more severe conditions in THF.