A novel series membranes based on non-linear all-aromatic polyimides (PIs) was investigated with the aim to understand how the PI backbone geometry and local electrostatics govern gas transport and the ability to separate CO₂/CH₄ mixtures. Non-linear 3-ring aromatic diamines, with exocyclic bond angles varying between 120 and 134°, enable the design of high Tg (>276 °C) PIs. A polar 1,3,4-oxadiazole diamine (ODD) (μ = 3D) monomer and a non-polar m-terphenyl diamine (TPD) reference monomer were synthesized and coupled with 3 dianhydrides, i.e. ODPA, ODDA, and 6FDA. In 6FDA-based membranes CO₂ permeabilities (P_CO2) are the highest of the series. The 6FDA-ODD membrane shows excellent membrane performance with high P_CO2 values at all feed pressures. Up to 12 bar (6 bar CO₂) none of the membranes reached their plasticization pressure. The non-linear backbone geometry promotes CO₂ permeability, whereas the presence of an electrostatic dipole moment associated with the 1,3,4-oxadiazole heterocycle governs CO₂/CH₄ separation selectivity.

Combining polymers with small amounts of stiff carbon-based nanofillers such as graphene or graphene oxide is expected to yield low-density nanocomposites with exceptional mechanical properties. However, such nanocomposites have remained elusive because of incompatibilities between fillers and polymers that are further compounded by processing difficulties. Here we report a water-based process to obtain highly reinforced nanocomposite films by simple mixing of two liquid crystalline solutions: a colloidal nematic phase comprised of graphene oxide platelets and a nematic phase formed by a rod-like high-performance aramid. Upon drying the resulting hybrid biaxial nematic phase, we obtain robust, structural nanocomposites reinforced with graphene oxide.

The thermoelectric properties of amorphous and semi-crystalline high-performance polyetherimide–SWCNT nanocomposites are reported for the first time. Nanocomposites based on a non-linear polyetherimide (PEI) model system, labeled aBPDA-P3, with 0.6, 4.4 and 10 vol% SWCNTs remained amorphous after the addition of SWCNTs. In contrast, SWCNTs induced crystallization in a linear PEI model system labeled as ODPA-P3. The (thermo)mechanical properties were fully characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMTA). The electrical conductivity was studied by four-probe measurements and showed higher values for the ODPA-P3 films reaching 20 S/m at 10 vol% of SWCNTs. The thermoelectric performance revealed by Seebeck coefficient (S) measurements showed values of 40 and 55 μV/K for the 0.6 and 4.4 vol% ODPA-P3 SWCNT nanocomposites, while 16 and 47 μV/K for aBPDA-P3 amorphous films. This enhancement has been attributed to SWCNT–induced crystallization in ODPA-P3 matrix. The PEI-SWCNT nanocomposites are ideal candidates as organic flexible films and coatings for large area thermal energy harvesting, where high temperature gradients exist. Potential applications can be envisaged in the aerospace, automotive and micro-electronics sectors.