Hyperbranched polyethoxysiloxanes were prepared via a one-pot synthetic route based on a condensation reaction of tetraethoxysilane with acetic anhydride in the presence of an organotitanium catalyst. Volatile compounds can be fully removed using a thin-film evaporator. According to size-exclusion chromatography and viscosity measurements, the average molecular weight as well as the molecular weight distribution of the products increased exponentially by increasing the molar ratio of acetic anhydride to tetraethoxysilane from 1.0 to 1.2. At the molar ratio 1.3, a solid gel was formed. The liquid products are stable and hydrophobic; they are miscible with most organic solvents. 29Si NMR spectroscopy and MALDI-ToF mass spectrometry show that they have a hyperbranched structure with additional internal loop formation.

We have synthesized polyethoxysiloxanes starting from the AB3‐type monomers triethoxysilanol and acetoxytriethoxysilane. The polymers are liquid and soluble in organic solvents. 29Si NMR spectroscopy and MALDI‐ToF mass spectrometry analyses show that the polymers have a hyperbranched structure with additional internal cyclization. 29Si NMR spectroscopy indicates that the polymer synthesized from acetoxytriethoxysilane is less branched than the polymer synthesized from triethoxysilanol. Analysis of the molar mass and mass distribution of the polymers via size exclusion chromatography (calibrated via MALDI‐ToF MS and viscosimetry) yields a molar mass of Mn ≈ 2 kg · mol−1 and Mw ≈ 8 kg · mol−1 for polymers synthesized from triethoxysilanol. The molar mass of the polymers synthesized from acetoxytriethoxysilane can be controlled by variation of the polymerization time in the range of Mn ≈ 1.8–12 kg · mol−1 and Mw ≈ 2.1–2 200 kg · mol−1. Photograph of a vial containing polyethoxysiloxane obtained from triethoxysilanol and a schematic drawing of the proposed molecular structure of the polymer.magnified imagePhotograph of a vial containing polyethoxysiloxane obtained from triethoxysilanol and a schematic drawing of the proposed molecular structure of the polymer.

Applying poly(ethoxysiloxane) (a liquid non-water-soluble polymer that can be hydrolyzed and cross-linked by diluted acids) to an air/pH 1 water interface gave rise to thin homogeneous solid layers. These layers were strong enough to be transferable to electron microscopy grids with holes of dimensions up to 150 microm and covered the holes as freely suspended membranes. No homogeneous layers were formed at an air/pH 5 water interface. Brewster angle microscopy images show that the poly(ethoxysiloxane) is not spontaneously forming a wetting layer on water. It initially forms lenses, which slowly spread out within several hours. We conclude that the spreading occurs simultaneously with the hydrolysis and cross-linking of the poly(ethoxysiloxane) and that the reaction products finally assist the complete wetting of the water surface.

No abstract