Nano/microfibrillated Cellulose as a Structure-Directing Template for One-Stage Synthesis of Ladder Polysilsesquioxane in Diluted Aqueous Solutions at Ambient Conditions

Abstract

Ladder polysilsesquioxanes with a closed cyclic structure are of great interest due to a combination of unique physical and chemical properties. Synthesis is performed using toxic organic solvents, catalysts, and expensive precursors and at high temperatures or in highly concentrated solutions. We describe an environmentally benign one-step formation of ladder polysilsesquioxanes in aqueous solutions on nano/microfibrillar cellulose aerogels. The synthesis is carried out by sol–gel chemistry using the precursor tris(2-hydroxyethoxy)methylsilane, which along with the methyl group contains three residues of ethylene glycol, facilitating the solubility of silane in water up to 20 wt %. This eliminates the use of organic─often toxic─solvents. The formation of ladder polysilsesquioxanes, as shown by attenuated total reflectance-Fourier transform infrared (FTIR) spectroscopy, occurs in dilute neutral solutions (≤0.1 M) without heating and the addition of a catalyst. The catalysis of the sol–gel process is achieved by nano/microfibrils, which are revealed by small-angle X-ray scattering. They also serve as a structure-directing template. The proposed mineralization of aerogels in the form of ladder polysilsesquioxanes coating, as demonstrated in a number of examples, opens up wide possibilities for the development of hydrophobic, mechanically strong, and flame-resistant materials for various applications.