Preparation of Polyethoxysiloxanes as a Solid (“a Solid Sol”) by Acid-Catalyzed Sol–Gel Reaction of Tetraethoxysilane

High Resolution Image Download MS PowerPoint Slide We successfully prepared polyethoxysiloxanes (PEOS) as solids with molecular weights ranging from 3700 to 12800, which have not been reported heretofore. PEOS was synthesized using three methods: (A) solvent removal under heating with a nitrogen flow, (B) refluxing, and (C) solvent evaporation by heating. In method B, PEOS was obtained as a solid regardless of molecular weight, which was comparable to the molecular weight in method A. Solid PEOS was soluble in organic solvents, insoluble in hexane, and exhibited stability against self-condensation, even with a high silica content of 57%–61%. It remained stable against self-condensation for over a year in a 40 wt % solution of tetrahydrofuran. The structure of PEOS was estimated to consist of either a local ladder or a cage structure, based on the relative ratio of the unit structures, Q n, and the results of spectral analysis. PEOS is regarded as a potential precursor for coatings because it produces coating films with a high pencil hardness of ≥4H.