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, δ and ε forms (δ e and ε e ). In this study, we have prepared high-purity nanoporous δ and ε 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 δ e form showed a complex phase transition behavior on heating, and at a higher temperature, the γ form (obtained through an intermediate helical phase) transformed into a mixture of α and β forms. On the other hand, the ε e form transformed directly into the γ form, and on further heating, the γ form transformed exclusively into the α form. The dielectric, thermal, and acoustic properties of crystallinenanoporous aerogels were promising with an ultralow dielectric constant (1.02 ± 0.02), thermal conductivity (λ) 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.

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The demand for biodegradable polymer-based aerogels with superior comprehensive properties has escalated in various fields of application, such as packaging, tissue engineering, thermal insulation, acoustic insulation, and environmental remediation. In this work, we report a facile strategy for enhancing the thermal and mechanical properties of polylactide (PLA) aerogels through the stereocomplex (SC) formation between the opposite enantiomers. Thermoreversible gelation of poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA) blend in crystal complex forming solvent and the subsequent thermal annealing of the gel resulted in crystalline pure SC gel, which, upon solvent exchange with water and freeze-drying, furnished robust SC aerogel. It was found that the SC content could be tuned by varying the annealing temperature of the blend gel and that we could prepare blend aerogels with pure α crystalline form and a mixture of α and SC. Crystalline pure blend α aerogel showed fibrillar morphology, whereas SC aerogel exhibited unique interwoven ball-like microstructures interconnected by PLLA and PDLA chains. The structural evolution during SC formation at the molecular level and the micrometer length scale instigated better properties in the PLA aerogels. When compared with the homopolymer aerogels, the crystalline pure SC aerogel showed an enhanced melting temperature of 227 ± 2 °C (50 °C higher), better thermal stability (onset of degradation was delayed by ∼40 °C), enhanced mechanical strength (compression modulus of 3.3 MPa), and better sound absorption ability. The biodegradability of PLA and the superior properties induced by stereocomplexation make these aerogels potential candidates for applications such as tissue engineering scaffolds, packaging, acoustic insulation, etc.