Preparation and properties of borosiloxane gels

Abstract

Hybrid gels were synthesized from modified silicon alkoxides (R-Si(OEt) 3 , R ϭ H, Me, Vi) and triisobutylborate (B(O-RЈ) 3 , RЈ ϭ isoBu). The obtained gels were characterized by Fourier-transform infrared (FTIR), nuclear magnetic resonance (NMR), elemental analyses, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Boron atoms in the precursors were homogeneously dispersed in the siloxane network via Si-O-B bonds. The effect of the boron load on oxidation resistance of the gels, and the pyrolysis behavior of the borosiloxane gels with different substituents on silicon, were investigated using various techniques. The experimental results suggest that the addition of a proper fraction of boron alkoxide to the precursors can improve the oxidation stability of the gels, and decrease the weight loss of the samples to 6.9 wt % at 1000°C under air.

Thermal properties of polymethylvinylborosiloxanes

“…The increase of the thermal stability with the increasing boron content, as determined by the indicator T 50 , was also observed-in the following order of PMVBSs: B 3 , we obtain that under air atmosphere PMVBSs characterize lower thermal stabilities than for the polymethylsiloxanes bearing only methyl groups or functional hydrosiloxane or vinylsiloxane groups in macromolecules [38].…”

“…The absorption bands corresponding to vibrations of the following groups of atoms: Si-CH 3 The chemical structure of the PMVBSs was confirmed by 1 H-, 29 Si-, 11 B-NMR methods . In the 1 H-NMR spectra of PMVBSs (e.g., Fig.…”

“…(1) The presence of two kinds of branching units (boron atoms and methylsiloxane units CH 3 SiO 1.5 ), (2) The different degrees of branching (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15), (3) The different contents of boron, (4) The different values of MWs, (5) The lengths of the siloxane chains between branching points (boron atoms and MeSiO 1.5 units), and (6) The different functionalities (the contents of vinylsiloxane groups).…”

“…The calibration of the spectrometer was done with an ICP multi-element standard solution VI for ICP-MS (Merck). Samples for the analysis were dissolved in concentrated acid solutions of spectral grade (HNO 3 and H 2 SO 4 ) in an MLS 1200 device (Milestone, Italy), with the application of microwaves.…”

“…Although it is known from the literature information that the presence of trivalent metals causes increase of thermal stability of materials, nevertheless an effect of boron atoms on thermooxidative stability under air atmosphere was studied so far only in a limited range [3]. Thermogravimetric studies proved a high thermal stability of PBS, which is the result of high dissociation energy of Si-O and B-O bonds, and moreover it is the result of high crosslinking degree of these polymers and the presence of phenyl groups in their macromolecules.…”