Abstract
Hierarchically porous crystalline nanoporous aerogels of syndiotactic polystyrene (sPS) received much attention because of their unique nanoporous structures along with meso- and macroporosity. Depending on the difference in the packing of polymer chains within the crystal lattice, sPS has two nanoporous crystalline forms, namely, (5 and e forms ((5e and ee). In this study, we have prepared high-purity nanoporous (5 and e forms of sPS aerogels from their respective gels using a solvent exchange strategy with green solvents, followed by an environmentally friendly freeze-drying technique. Using these highly porous aerogels, the phase transition behavior of sPS at higher temperatures was investigated. The (5e form showed a complex phase transition behavior on heating, and at a higher temperature, the y form (obtained through an intermediate helical phase) transformed into a mixture of a and fi forms. On the other hand, the ee form transformed directly into the y form, and on further heating, the y form transformed exclusively into the a form. The dielectric, thermal, and acoustic properties of crystallinenanoporous aerogels were promising with an ultralow dielectric constant (1.02 +/- 0.02), thermal conductivity (A) as low as 0.04 W m-1 K-1, and a high sound absorption coefficient (close to 1). Moreover, these aerogels exhibited excellent oleophilicity, which was demonstrated in oil/organic solvent separation experiments. These multifunctional aerogels of sPS can, therefore, find a multitude of applications, especially in thermal and acoustic insulation and molecular sorption of oil/organic solvents.