Primary silanes, polymerization mechanism

Silanes. Group IVB metallocenes catalyze the stepwise polymerization (dehydrocoupling) of primary silanes, yielding H—(SiHR) —H and n H2 (232). The mechanism appears to he strictly metathetical for such molecules as (Cp)(C5(CH3)5)Hf(X) (R = H, alkyl X = H, alkyl, chloride), wherein the entire process takes place on the neutral manifold (Scheme 11) (233). 

Three primary mechanisms have been suggested for enhanced adhesion via silane coupling agents.5 The classical explanation is that the functional group on the silane molecule reacts with the adhesive resin. Another possibility is that the polysiloxane surface layer has an open porous structure. The liquid adhesive penetrates the porosity and then hardens to form an interpenetrating interphase region. The third mechanism applies only to polymeric adherends. It is possible that the solvent used to dilute and apply the silane adhesion promoter opens the molecular structure on the substrate surface, allowing the silane to penetrate and diffuse into the adherend. 

---