The recovery and reuse of high-impact polystyrene (HIPS) into high-value products is crucial for reducing environmental thermoplastics waste and promoting sustainable materials for various applications. In this study, asymmetric membranes obtained from sulfonated HIPS waste were used for salt and dye removals. The incorporation of sulfonic acid (-SO₃H) groups into HIPS waste by direct chemical sulfonation with chlorosulfonic acid (CSA), at two different concentrations, was investigated to impart antifouling properties in membranes for water treatment. Asymmetric membranes from recycled HIPS, R-HIPS, R-HIPS-3, and R-HIPS-5 with 3 and 5% sulfonation degrees, respectively. Sulfonated HIPS shows a decrease in water contact angle (WCA) from 83.8° for recycled R-HIPS to 66.1° for R-HIPS-5, respectively. A WCA decrease leads to an increase in antifouling properties for R-HIPS-5, compared to non-sulfonated R-HIPS, which leads to a higher flux recovery ratio (FRR) and enhanced separation properties for sulfonated membranes. The HIPS-5 membrane exhibited the highest rejection rates for Reactive Black 5 dye (94%) and divalent salts (72% for MgSO₄ and 67% for Na₂SO₄). The performance of the recycled HIPS asymmetric membranes is well correlated with porosity, water uptake, and the higher negative charge from the sulfonic acid groups present, which enhance the electrostatic repulsions of salts and dyes.

Four polyimides based on bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTD), BTD-MIMA, BTD-HFA, BTD-FND, and BTD-TPM, with different rigid substituted diamines were synthesized. The chemical structure of the polyimides was corroborated by 1H NMR spectroscopy. These polyimides were soluble in organic solvents and presented molecular weights (Mn) between 39 and 70 KDa. BTD-MIMA, BTD-HFA, BTD-FND, and BTD-TPM showed thermal stability above 400 °C. These polyimides also presented high glass transition temperatures between 272 and 355 °C. The alicyclic moiety increased solubility compared with other rigid polyimides. Membrane films from BTD-MIMA and BTD-HFA exhibited the highest gas permeability compared to BTD-FND and BTD-TPM. The introduction of ortho-substituents in BTD-MIMA or bulky –CF3 groups in BTD-HFA, in combination with the alicyclic dianhydride fragment, prevented chain packing and enhanced macromolecular chain rigidity. In turn, there was a shift toward higher gas permeability coefficients for BTD-MIMA and BTD-HFA, with a moderate loss of CO₂/N₂ and CO₂/CH₄ selectivity, and they presented similar selectivities to those of other reported polyimides with alicyclic BTD moieties containing asymmetric fragments.