Synthesis and Characterization of Ultralight Syndiotactic Polystyrene Aerogels Prepared by Freeze-Drying

We have developed a strategy to synthesize high-quality ultralight (<10 mg/cm³) syndiotactic polystyrene (sPS) aerogels. The ultralight sPS aerogels with the same shape as gels were prepared via direct freeze-drying of <i>p</i>-xylene-based sPS gels without cumbersome solvent exchange steps. Due to the high melting point of <i>p</i>-xylene (13 °C), it can be solidified during the freeze-drying process, and no solvent exchanges were required to suppress the collapse during the formation of sPS aerogels, unlike in typical sPS aerogel preparation. The ultralight sPS aerogels with the highest porosity of 99.6% and the lowest density of 4.5 mg/cm³ can be easily prepared. Morphological analysis of the ultralight aerogels confirmed that the 3D fibrous network structure was formed after <i>p</i>-xylene sublimation. The dielectric constant of the ultralight sPS aerogels (κ = 1.01) represents the lowest value ever reported for polymer-based aerogels, closely approaching that of air. In particular, their ultralow density, ultrahigh porosity, highly hydrophobic and oleophilic properties, adequate mechanical strength, and interconnected porous fiber-like structure make them suitable adsorbents for oil and organic solvents, which are promising candidates for removing pollutants and separating oil and water. The structural and property changes of the ultralight aerogels induced by annealing above <i>T</i>_g of sPS were comprehensively analyzed. This simple aerogel preparation method can utilize the ultralight sPS aerogel framework as a suitable scaffold for preparing composite materials, which is conducive to enhancing the properties and extending the applications of sPS aerogels in various fields.