Sol-gel reactions of 3-glycidoxypropyltrimethoxysilane in a highly basic aqueous solution

Abstract

The reactions of 3-glycidoxypropyltrimethoxysilane in a highly basic aqueous solution have been studied by multinuclear magnetic resonance and light scattering techniques. The study has shown that in this peculiar chemical environment the alkoxy groups of 3-glycidoxypropyltrimethoxysilane undergo a fast hydrolysis and condensation which favor the formation of open hybrid silica cages. The silica condensation reaches 90% at a short aging time but does not go to completion even after 9 days. The highly basic conditions also slow down the opening of the epoxies which fully react only after several days of aging. The epoxy opening generates different chemical species and several reaction pathways have been observed; in particular, the formation of polyethylene oxide chains, diols, termination of the organic chain by methyl ether groups and formation of dioxane species. These reactions are slow and proceed gradually with aging; light scattering analysis has shown that clusters of dimensions lower than 20 nm are formed after two days of reactions, but their further growth is hindered by the highly basic conditions which limit full silica condensation and formation of organic chains.

Epoxide Opening versus Silica Condensation during Sol–Gel Hybrid Biomaterial Synthesis

“…The hydrolysis of the alkoxysilane groups, the formation of the Si‐O‐Si network by using condensation, and the opening reaction of the epoxide ring of GPTMS are strictly dependent on different variables, such as the character of the solvent, the amount of water present, the catalyst,26 the temperature, and the nature of the alkoxy groups bounded to the silicon atom in these reactions 21. Moreover, the pH value is key for the hydrolysis of the epoxide and silyl alkoxy groups and influences the outcome of the condensation reaction.…”

“…In this respect, a comprehensive study of the epoxide opening versus silicon condensation reaction of 3‐glycidoxypropyltrimethoxysilane (GPTMS) as a function of pH value is still missing, despite initial efforts on this topic 20. To the best of our knowledge, studies on GPTMS reactivity on its own have been reported at very high pH values21–23 or at acidic pH values in the presence of Lewis acids such as boron trifluoride etherate,19b titanium chloride,24 or metal (alk)oxides 25–27. Herein, we propose the NMR spectroscopic and mass spectrometric study of GPTMS behaviour as a function of pH value to compare the reactivity of silicon condensation against epoxide opening at different pH values.…”

Formation of a conductive overcoating layer based on hybrid composites to improve the stability of flexible transparent conductive films

“…These epoxy groups caused the formation of many hydroxy groups on the surface of silica sol through ring-opening reactions under acidic conditions. [24][25][26] Poly(4-styrenesulfonic acid) (PSSA) containing sulfonic acid, which is water-soluble and acidic, was used so that the silica precursor could form a sol. Subsequently, the network structure through the binding of hydroxyl groups and sulfonic acid on the surface of silica sol was induced under thermal conditions.…”

Crystallization in hybrid organic-inorganic materials through self-organization from 3-glycidoxypropyltrimethoxysilane

“…If GPTMS is dissolved in an aqueous solution of NaOH to reach a pH > 13, the conditions that we have previously described are fulfilled; the sol can be used for deposition of films or for preparing bulk gels upon controlled aging. 44) A good description of the reactions that happen in the sol is obtained by 13 C NMR; Fig. 3 shows the 13 C NMR spectra of GPTMS in a highly basic solution as a function of the aging time.…”