Synthesis of high-performance polymethylsilsesquioxane xerogels by improving acid catalytic conditions in aluminum chloride aqueous solution

Abstract

Organic and inorganic acids are common catalysts to promote the hydrolysis of methyltrialkoxysilanes, but they are challenging to modulate the inherent CH3SiO1.5 backbone of polymethylsilsesquioxane (PMSQ) xerogels. Here, an aluminum chloride aqueous solution is proposed for the first time as an acid catalyst to enhance the hydrolysis of methyltriethoxysilane (MTES). This approach allows the PMSQ xerogels to have a more flexible [-Al-O-]m-[SiO]n backbone structure. The optimal concentration of aluminum chloride and surfactant cetyltrimethylammonium bromide in the MTES sol was 1.069 mmol/L and 0.885 mmol/L, respectively, endowing the as-synthesized PMSQ xerogel with a high compression strength of 0.450 MPa and maximum compression strain of 76.1%. Notably, the tiny incorporation of alumina phase (0.4 mol%) in the Si-O-Si backbone made the PMSQ xerogels hydrophobic up to 400 °C for 1 h in the air. The PMSQ xerogels possessed superior thermal insulation properties (32.0–38.0 mW/(m·K)) and could be processed into desired large-sized shapes.