Polymerization of Bis(triethoxysilyl)ethenes. Impact of Substitution Geometry on the Formation of Ethenylene- and Vinylidene-Bridged Polysilsesquioxanes

Abstract

In this study, we utilized the substitution geometry of triethoxysilyl groups about an organic bridging group to control the outcome of the sol-gel polymerization process. The substitution geometry of two triethoxysilyl groups about a carbon-carbon double bond was determined to have a profound effect on sol-gel polymerizations of the E (1) and Z (2) ethenylene-bridged monomers and vinylidene-bridged monomer (3) and on the porosity in the resulting xerogels. 29 Si NMR and chemical ionization mass spectrometry were used to elucidate the early sol-gel chemistry in the acid-catalyzed polymerizations of 1-3. Trans substitution about the ethenylene-bridging group in 1 led to acyclic and monocyclic dimers and trimers as condensation products under acidic conditions and only microporous gels under both acidic and basic conditions. In contrast, cyclization reactions dominated the sol-gel chemistry of 2 beginning with intramolecular cyclization to give the cyclic disilsesquioxane (4) and continued with the formation of cyclic oligomers, including a bicyclic dimer. The cyclization of 2 slowed the rate of gelation compared to 1 and afforded microporous xerogels under acidic conditions and mesoporous gels under basic conditions. The sol-gel chemistry of the vinylidene monomer (3) was strongly retarded by the formation of a cyclic dimer (5). Only mesoporous gels were formed under basic conditions after 9 months; no gels were obtained under acidic conditions.

Characterization of a non‐organofunctional silane film deposited on Al, Zn and Al–43.4Zn–1.6Si alloy‐coated steel

“…where the first ion can be formed by a simple cleavage of an Si-O bond, but for the rest of the structures to be formed two bonds must be cleaved and hydrogen must be captured. Although the latter process is possible, the former process is more reasonable to assume, and cyclic structures formed by intramolecular condensation have been reported 14 to be formed under acidic conditions.…”

To stir or not to stir: formation of hierarchical superstructures of molecularly ordered ethylene-bridged periodic mesoporous organosilicas

“…Materials synthesis 1,2-Bis(triethoxysilyl)ethylene (BTEE) was synthesized as previously reported. 17 Only the distilled fraction with a boiling point higher than 90 uC/15 mm Hg was used. The synthesis procedure designated as under 'static conditions' was as follows: 4.75 g cetyltrimethylammonium bromide (CTAB) was dissolved in 64.87 g distilled water under stirring in a 250 ml polypropylene bottle, followed by addition of 0.96 g NaOH to control the pH value.…”

Systematic extension of the length of the organic conjugated π-system of mesoporous silica-based organic–inorganic hybrid materials

“…The precursors 1-3 were synthesised according to standard literature procedures. 14,17,18 The synthesis of the new (pure hydrocarbon) organosilane precursor (4) was accomplished via a two-step synthesis with (E)-4,4 0 -dibromostilbene as an intermediate. 19 In the second step a palladium-catalysed double Heck coupling of (E)-4,4 0dibromostilbene with vinyltriethoxysilane was carried out.…”