Mechanism and Kinetics of Oligosilsesquioxane Growth in the In Situ Water Production Sol–Gel Route: Dependence on Water Availability

Abstract

Thiol-functionalized nanobuilding blocks (NBBs) were synthesized from 3-mercaptopropyltrimethoxysilane by using the in situ water production (ISWP) process in which the water needed to hydrolyze the precursor was provided by means of an esterification reaction. In the present study the reaction between 1-propanol and chloroacetic acid was used. Whereas the growth of the Si oligomers was followed at room temperature and 100°C using 1D 29 Si and 2D 1 H-29 Si heteronuclear single quantum correlation (HSQC) NMR spectroscopic experiments, the amount of water delivered along the process was followed by means of 1 H NMR spectroscopy. The results show a good correlation between the evolution of the degree [a]

Architecture of Silsesquioxanes

“…For instance, with the 3-mercaptopropylsilane derivatives HSCH 2 CH 2 CH 2 Si(OPr) x (OMe) y (OH) 3-(x+y) , Borovin et al have observed a high frequency shift of 1.26 AE 0.02 ppm for the replacement of a propoxy by a methoxy group, regardless of the extend of hydrolysis. High-frequency shifts in the range 0.9-0.6 ppm and 2.2-1.8 ppm were also observed for the hydrolysis of a methoxy and propoxy group, respectively (Borovin et al 2016b). An additional source of Si solution NMR spectra, with the T n chemical shift zones, for silsesquioxanes obtained by the ISWP sol-gel route from 3-mercaptopropyltrimethoxysilane, propanol, chloroacetic acid, and dibutyltin dilaurate (1:18:6:0.015) after different reaction times at 100 C (Borovin et al 2016b) high-frequency shifts is the reduction of the valence angles related to the formation of short strained cycles such as the 6-membered ones.…”

“…High-frequency shifts in the range 0.9-0.6 ppm and 2.2-1.8 ppm were also observed for the hydrolysis of a methoxy and propoxy group, respectively (Borovin et al 2016b). An additional source of Si solution NMR spectra, with the T n chemical shift zones, for silsesquioxanes obtained by the ISWP sol-gel route from 3-mercaptopropyltrimethoxysilane, propanol, chloroacetic acid, and dibutyltin dilaurate (1:18:6:0.015) after different reaction times at 100 C (Borovin et al 2016b) high-frequency shifts is the reduction of the valence angles related to the formation of short strained cycles such as the 6-membered ones. This last effect generally represents a variation of 2-4 ppm for T 2 species (Brunet 1998;Matejka et al 2000), but it can be stronger as shown by the 29 Si chemical shifts of [(c-C 6 H 11 )SiO 1.5 ] 6 and [(c-C 6 H 11 )SiO 1.5 ] 8 , which equal À56 and À69 ppm, respectively (Feher et al 1989;Bassindale et al 2003).…”

“…They are then transformed into hydrodynamic sizes with the Stokes-Einstein equation. Borovin et al recently applied this methodology to study the limited growth of oligosilsesquioxanes in the in situ water production sol-gel route (Borovin et al 2016b). Such an NMR-based technique appears quite complementary to size exclusion chromatography (SEC) as it can provide site selective information.…”

“…However, in over-stoichiometric conditions (r = 6), condensation degree, cage-to-ladder ratio, and size distribution of oligosilsesquioxanes appear unaffected by the catalyst choice and mainly ruled by the kinetics of ISWP process. The dependence of architecture on water availability during ISWP sol-gel condensation was clearly elucidated by studying the esterification kinetics and its effect onto the silsesquioxane growth by NMR time-dependent monitoring of reaction run at room temperature and 100 C with a fixed hydrolysis ratio (r = 6) and DBTL as catalyst (Borovin et al 2016b). By measuring the extent of hydrolysis-condensation (Fig.…”

Hydrophobic Coatings by Thiol-Ene Click Functionalization of Silsesquioxanes with Tunable Architecture

“…The extent of hydrolysis–condensation in dependence on the kinetics of water production was assessed by time-dependent monitoring of the reactions, mainly through infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC) analyses, demonstrating the ability to tune SSQs’ size and architecture by simply controlling the reaction duration. In particular, in the case of thiol-functionalized SSQs (SH-NBBs) [ 14 ], obtained by controlled hydrolysis-condensation of 3-mercaptopropyltrimethoxysilane (McPTMS) with chloroacetic acid (ClAAc) in 1-propanol solution at 100 °C ( Figure 1 a), the well-defined octakis (3-mercaptopropylsilsesquioxane) is the major species between 70 and 100 h reaction time; on the contrary, the ladder-like species appeared predominant for lower duration, according to 29 Si NMR spectroscopy [ 15 ]. However, the ISWP route is characterized by the occurrence of different reactions ( Figure 1 b,c), leading also to side products such as chloroacetic acid-derived compounds that cannot be completely removed from the SH-NBBs solution.…”