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

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 × 10(3) 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.