One-Pot Synthesis of Hyperbranched Polyethoxysiloxanes

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.