Synthesis of silanol-rich long-life polysilsesquioxane liquids by cosolvent-free hydrolytic polycondensation of organotrimethoxysilanes followed by aging

Abstract

Polysilsesquioxane (PSQ) liquids have been prepared from propyltrimethoxysilane–water and trimethoxy(3-sulfanylpropyl)silane–water binary systems without the use of organic solvents through hydrolytic polycondensation followed by aging. By introducing the aging step, the viscosity of the as-prepared PSQ liquid is decreased by more than an order of magnitude, and the long-term viscosity stability is improved considerably. These variations are mainly attributed to the modification of the topology of the Si–O–Si network because the crosslinking density was influenced little by the aging. The viscosity of PSQ liquids obtained via aging at 80 °C was ∼4–5 × 10³ mPa s at 30 °C and the viscosity increase was less than 25% after storage for 2 months at room temperature despite the many unreacted silanol (SiOH) groups present in the liquid.