Low-Density, Semicrystalline Poly(phenylene sulfide) Aerogels Fabricated Using a Benign Solvent

Utilizing a thermally induced phase separation process, poly(phenylene sulfide) (PPS) thermoreversible gels are developed using for the first time a benign solvent, 1,3-diphenylacetone (DPA). The PPS/DPA phase diagram revealed a solid–liquid phase separation mechanism often observed with crystallizable polymers in good solvents. Two different methods of determining the Flory–Huggins interaction parameter, χ, were utilized to understand the polymer–solvent interactions that govern the phase behavior. Using an experimental approach, a melting point depression curve was fit to experimental PPS/DPA melting point data, revealing an interaction parameter of χ = 0.41. Using accepted Hansen solubility parameters of PPS and calculated parameters for DPA via a group contribution method, the polymer–solvent interaction parameter was estimated to be χ = 0.49. The reasonable agreement between both methods indicates good interactions between PPS and DPA and verifies the calculated solubility parameters for DPA. Upon gelation at temperatures below 225 °C, subsequent solvent evacuation via freeze–drying yields aerogels with low densities ranging from 0.11 to 0.25 g/cm3 and volumetric porosities ranging from 92.3 to 82.2%. The physical properties of the PPS aerogels were found to be comparable to similar aerogels made from poly(ether ether ketone) (PEEK). Ultra-small to wide-angle X-ray scattering (USAXS/SAXS/WAXS) profiles reveal an ordered, hierarchical morphology with sharp interfaces, whereby the microstructure is composed of semicrystalline aggregates of stacked lamella. Scanning electron microscopy micrographs indicate that the PPS aerogels are highly porous and that the lamellar stacks take the form of elongated, interconnected fibrils. Power-law scaling of aerogel density with compressive modulus suggests a tendency of the interconnected lamellar aggregates to bend and/or buckle in compression in a manner similar to strut deformation in open-celled foams. Despite their similar physical properties, PPS aerogels demonstrated higher moduli than PEEK aerogels at comparable densities due to their network-like morphology.