Thermodynamics and conformation of PPPO in mixed solvents: towards nanoporous polymeric gas sensors

Poly(2,6-diphenyl-p-phenylene oxide) (PPPO) can be processed into high performance nanoporous materials, with applications ranging from gas separations to sensing. An attractive design route involves demixing from solution, generally via spinodal decomposition induced by non-solvent addition, and followed by phase inversion and kinetic arrest. In this work, we investigate the thermodynamics and phase separation of the ternary PPPO/solvent/non-solvent system, combining light and Small Angle Neutron Scattering, and electron microscopy.
We determine the polymer conformation and interaction parameters in binary and ternary solutions across the concentration range relevant for porous polymer formation. Combined with viscosimetry measurements, we establish overlap and concentrated crossovers, c* and c**, and obtain radii of gyration R_g and its dependence on concentration in mixed solvents, as well as the respective χ parameters. We then determine the demixing pathway for the polymer-rich phase, approaching the glass transition and resulting in its kinetic arrest. Based on these results, we establish a predictive and versatile design strategy for PPPO nanoporous gas adsorbers.