Hydrophobic Aerogels from Vinyl Polymers Derived from Radical Polymerization: Proof-of-Concept

Hydrophilicity is one important drawback of bio-based aerogels. To overcome this issue, a novel approach for the preparation of mesoporous, water repellent aerogels is introduced, which combines synthesis of cross-linked bio-based copolymers from methacrylate copolymerizations, followed by solvent exchange and supercritical drying steps. The influence of monomers with different nonpolar ester groups (methyl, vanillin, tetrahydrofurfuryl) on textural properties and water contact angles of the dry products is assessed. Final aerogels show generally high overall porosities (approximate to 96%), low densities (0.07-0.11 g cm-3) as well as fine, mainly mesoporous networks, and specific surface areas in the range of 120-240 m2 g-1. Hereby, choice of the methacrylate ester groups results in differences of the resulting pore-size distributions. Water repellency tests show stable static water contact angles in the hydrophobic range (approximate to 100 degrees) achieved for the substrate containing the vanillin ester group. On the contrary the other substrates absorb water quickly, which indicates a decisive role of the ester group. The presented approach opens up a new pathway to bio-based aerogels with intrinsic hydrophobicity. It is suggested that the properties are tailored by the choice of the monomer structure, hence enabling further adaption and optimization of the products. A novel type of aerogels prepared from copolymers obtained via free-radical polymerization of partially bio-based methacrylates and styrene is reported. Common to all materials are high overall porosities and specific surface areas, low densities, and mainly mesoporous networks, with all properties depending on the ester group structure. The aerogel prepared with vanillin methacrylate (VMA) shows very good liquid water repellent properties. image