The following work shows, for the first time, the synthesis and characterization of a new family of polyelectrolytes, along with their preliminary assessments in terms of desalin water treatment. These materials fall into the category of aromatic co-polyamides, which are obtained by the direct condensation of monomers 4,4′-oxydianiline (ODA), isophthaloyl chloride, and 3,5-diamino-N-(pyridin-4-ylmethyl)benzamide (PyMDA). Thereby, the charged nature exhibited by these materials was achieved through the quaternization of PyMDA moieties using linear iodoalkanes of different lengths (C_nI with n = 1, 2, 4, and 6). After completing the quaternization process, polyelectrolytes were subjected to a one-step anion substitution process, where iodide counterions were replaced by bis(trifluoromethane)sulfonamide entities. For all the obtained materials, solubility tests were carried out, showing that those alkylated with methyl and ethyl chains exhibit high solubility in rutinary aprotic polar solvents, while those containing n-butyl and n-hexyl units resulted in the formation of insoluble gels. Due to the above, the latest were discarded from this study early on. The structural characterization of the initial neutral co-polyamide was carried out by means of infrared spectroscopy (FT-IR), nuclear magnetic resonance (¹H, ¹³C-NMR), and size-exclusion chromatography (SEC), while the structure of methylated and ethylated polyelectrolytes was successfully confirmed through FT-IR, ¹H, ¹³C, and ¹⁹F-NMR. Additionally, the thermal behavior of these materials was analyzed in terms of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), showing thermal degradation temperatures above 300 °C and glass transition temperatures (Tg) above 200 °C, resulting in polymers with outstanding thermal properties for water treatment applications. On the other hand, through the solvent-casting method, both neutral and charged polymers were found to be easily prepared into films, exhibiting a remarkably flexibility. The mechanical properties of the films were analyzed using the traction test, from which tensile strength values ranging between 83.5 and 87.9 Mpa, along with Young’s modulus values between 2.4 and 2.5 Gpa were obtained. Moreover, through contact angle measurements and absorption analysis by immersion, polyelectrolytes showed important changes in terms of affinity against polar and polar substances (water, n-heptane, and benzene), exhibiting a higher rejection regarding the neutral polymer. Finally, as a preliminary test against the seepage of saline waters, thin polymer films (from 11.4 to 17.1 µm) were deposited on top of commercial filter discs and tested as filters of saline solutions ([NaCl] = 1000 and 2000 ppm). These tests revealed a decrease of the salt concentration in the obtained filtrates, with retention values ranging between 6.2 and 20.3%, depending on the concentration of the former solution and the polymer used.

In this research, novel, organic, solid-liquid phase-change materials (PCMs) derived from methoxy polyethylene glycol (MPEG) and aromatic acyl chlorides (ACs) were prepared through a condensation reaction. The MPEGs were used as phase-change functional chains with different molecular weights (350, 550, 750, 2000, and 5000 g/mol). The aromatic ACs, terephthaloyl chloride (TPC) and isophthaloyl chloride (IPC), were employed as bulky linker cores. Solubility tests demonstrated that this family of PCMs is soluble in protic polar solvents such as H₂O and MeOH, and insoluble in nonpolar solvents such as n-hexane. Fourier-ransform infrared spectroscopy (FT-IR UATR) and nuclear magnetic resonance (¹H, ¹³C, DEPT 135°, COSY, HMQC, and HMBC NMR) were used to confirm the bonding of MPEG chains to ACs. The crystalline morphology of the synthesized materials was examined using polarized optical microscopy (POM), revealing the formation of spherulites with Maltese-cross-extinction patterns. Furthermore, it was confirmed that PCMs with higher molecular weights were crystalline at room temperature and exhibited an increased average spherulite size compared to their precursors. Thermal stability tests conducted through thermogravimetric analysis (TGA) indicated decomposition temperatures close to 400 °C for all PCMs. The phase-change properties were characterized by differential scanning calorimetry (DSC), revealing that the novel PCMs melted and crystallized between −23.7 and 60.2 °C and −39.9 and 45.9 °C, respectively. Moreover, the heat absorbed and released by the PCMs ranged from 57.9 to 198.8 J/g and 48.6 to 195.6 J/g, respectively. Additionally, the PCMs exhibited thermal stability after undergoing thermal cycles of melting-crystallization, indicating that energy absorption and release occurred at nearly constant temperatures. This study presents a new family of high-performance organic PCMs and demonstrates that the orientation of substituent groups in the phenylene ring influences supercooling, transition temperatures, and thermal energy storage capacity depending on the MPEG molecular weight.

Ionenes are poly(ionic liquids) (PILs) comprising a polymer backbone with ionic groups along the structure. Ionenes as solid–solid phase change materials are a recent research field, and some studies have demonstrated their potential in thermal dissipation into electronic devices. Eight ionenes obtained through Menshutkin reactions were synthesized and characterized. The analysis of the thermal tests allowed understanding of how the thermal properties of the polymers depend on the aliphatic nature of the dihalogenated monomer and the carbon chain length. The TGA studies concluded that the ionenes were thermally stable with T_10% above 420 °C. The DSC tests showed that the prepared ionenes presented solid–solid transitions, and no melting temperature was appreciated, which rules out the possibility of solid–liquid transitions. All ionenes were soluble in common polar aprotic solvents. The hydrophilicity of the synthesized ionenes was studied by the contact angle method, and their total surface energy was calculated. Self-healing behavior was preliminarily explored using a selected sample. Our studies show that the prepared ionenes exhibit properties that make them potential candidates for applications as solid–solid phase change materials.

This study explores the development and evaluation of a novel series of aromatic co-polyamides featuring diverse pendant groups, including phenyl and pyridinyl derivatives, designed for water desalination membrane applications. These co-polyamides, synthesized with a combination of hexafluoroisopropyl, oxyether, phenyl, and amide groups, exhibited excellent solubility in polar aprotic solvents, thermal stability exceeding 350 °C, and the ability to form robust, flexible films. Membranes prepared via phase inversion demonstrated variable water permeability and NaCl rejection rates, significantly influenced by the pendant group chemistry. Notably, pyridinyl-substituted membranes achieved water fluxes up to 17.7 L m⁻² h⁻¹ and a NaCl rejection of 37.3%, while phenyl-substituted variants provided insights into the interplay of hydrophobicity and porosity. These findings highlight the critical role of pendant group functionality in tailoring membrane performance, offering a foundation for further structural modifications to enhance efficiency in water treatment technologies.

The following study presents the initial evaluation (solubility, thermal stability, antibacterial activity, and cytotoxicity) of a series of previously described organic salts, derived from the bis(4-aminopyridinium) cation with different chain lengths, for their potential use as hospital disinfectants. Of the salts studied, those with chain lengths between 2 and 10 carbon atoms (C₂–C₁₀) showed high solubility in water, methanol, and DMSO. All salts exhibited high thermal stability, showing a thermal decomposition temperature (T_5%) above 330 °C. Antibiotic susceptibility testing of the studied E. coli, S. aureus, and S. typhimurium strains confirmed their resistance to different classes of commonly used clinical antibiotics, validating their selection. During the determination of antibacterial activity, the long-chain salts (C₁₀ and C₁₂) showed the greatest activity, with minimum inhibitory concentrations (MICs) from 31.2 μg/mL to 62.5 μg/mL in all the strains studied. Given the high activity of C₁₀ and C₁₂, their cytotoxicity was assessed in HeLa cells. They exhibited no cytotoxic effects after 12 h and only about 5% cytotoxicity after 24 h. Furthermore, the cell viability assay of the most active and water-soluble salt, C₁₀, showed that this salt can interact with the bacterial cytoplasmic membrane, increasing its permeability in both Gram-positive and Gram-negative bacteria. However, these results cannot rule out the possibility that this salt may have more than one site of action within the bacterial cell.