Hydrolysis and condensation of silanes in aqueous solutions

Abstract

Aminosilanes hydrolyze rapidly in aqueous acidic solutions and exhibit good stability; however 1H NMR measurements indicate that γ‐MPS (γ‐methacryloxypropyltrimethoxy silane) hydrolyzes slowly and condenses rapidly under similar conditions. The rate constant of these two reactions depends upon the pH of the solution, and the rate constant of the condensation reaction also depends upon the initial γ‐MPS concentration. The hydrolysis is faster and the condensation slower at low pH's. These factors explain why an induction period is observed before the adsorption of γ‐MPS onto mica takes place and why it does not occur if the induction period is too long. Using the Lentz technique, it is also shown that the main species resulting from the condensation of a concentrated γ‐MPS solution is a cyclic trimer or tetramer, in agreement with literature results.

Reactions of a Trifunctional Silane Coupling Agent in the Presence of Colloidal Silica Sols in Polar Media

“…When Nishiyama and co-workers (28) examined the extent of chemisorption as compared with physisorption during adsorption of MPS from ethanol-water solutions, they found little adsorption until dimers were formed. Conversely, adsorption of MPS hydrolysates on mica was suppressed after prolonged prehydrolysis, presumably due to condensation proceeding to larger oligomers (31). Once a silane monolayer formed on mica, further MPS adsorption was not hindered by the continuing polymerization (32).…”

Silane adsorption onto cellulose fibers: Hydrolysis and condensation reactions

“…Both the hydrolysis and the condensation reactions of the silanol groups are affected by the structure of the organic part of the silane and by the medium composition (temperature, pH, concentration, amounts of water and catalyst) [19,20]. The extent of silane hydrolysis and its degree of oligomerization are known to exert a great influence on the silane adsorption and on its configuration at the substrate surface [21][22][23]. Therefore, these two parameters must be judiciously controlled in order to optimize the surface modification with silane coupling agents.…”

“…Even though the hydrolysis and condensation reactions of silanes have been investigated using different spectroscopic techniques such as FTIR [11,24], Raman [25], and NMR spectroscopy [16,21,23,26], the multitude of reactions likely to occur and their dependence on solvent composition makes it necessary to control the conduct of these reactions carefully to favor silane adsorption on the substrate surface.…”

Controllable synthesis of raspberry-like PS–SiO2 nanocomposite particles via Pickering emulsion polymerization

“…Under acidic conditions, the (CH 3 O) 3 -Si-groups of MPS molecules are inclined to hydrolyze into metastable Si-OH groups and further self-condense into low-molecular-weight linear and cyclic oligomers. [44][45][46][47] Normally, the condensation extent is relatively low under acidic conditions, and therefore, many silanol groups are remained in the silica oligomers. 48 Due to the coexistence of hydrophobic methacrylate groups and hydrophilic silanol ones, the silica oligomers display an amphiphilic property and are prone to be distributed on the surface of St monomer droplets, [49][50][51][52][53][54] functioning as emulsiers to form a stable milky white emulsion (Fig.…”

“…Under acidic condition, MPS molecules underwent hydrolysis reactions, producing hydrophilic or amphiphilic Si-OH groups enriched low-molecular-weight linear and even cyclical oligomers. 44 These amphiphilic Si-OH enriched oligomers are prone to distribute on the surfaces of the St monomer emulsion droplets, 62 which are easily to react with the ultrane silica particles with many Si-OH groups on their surfaces under basic promoted condensation reaction. Thus, without any added surfactants or polymeric stabilizers, the silica particles herein acted as emulsiers to stabilize the monomer droplets with the assistant of pre-hydrolyzed MPS.…”