Self-assembling polyimides (PIs) having diketopiperazine (DKP) components were synthesized by polycondensation of a 4-amino-L-phenylalanine (4APhe) dimer, an aromatic diamine newly designed in this study. The amino acid-derived PIs showed high thermal resistance, with a 10% weight loss temperature (T d10 ) of 432 °C at the maximum, and did not show any glass transition below the thermal decomposition temperature. The poly(amic acid) (PAA) precursors formed nanospheres upon reprecipitation over dimethylacetamide into water. The nanospheres were then added to solvents with different polarities and sonicated to induce deformation of the spherical forms into spiky balls, flakes, or rods. The PAA particle morphologies were retained in the PIs after the two-step imidization. Finally, the PI particles with self-assembling DKP moieties were formed, and their morphologies were fine-tuned using different mixed solvents.

Diketopiperazine-based polyamides have been synthesized from aspartame, and could self-assemble into particles with various morphologies in different solvents.

Anionic pollutants in water, especially radioactive iodide, have gained attention because of their adverse toxic side effects on humans. Recently, an exotic biobased amino acid, 4-amino cinnamic acid (4ACA), has been utilized to produce heat-resistant and UV-degradable biopolyamides. In this research, a multifunctional monomer, 4,4′-di­(trimethylamino)-α-truxillic acid (Q4-ATA), was synthesized by the quaternization of 4ACA and was polymerized with various diamines to obtain a series of biopolyamides. All biopolyamides are soluble in aprotic solvents and possess high thermal properties, with 10% weight loss temperatures of 296–329 °C. One application of these cationic biopolyamide-bearing quaternary ammonium was the anion-exchange ability, so they were employed to remove iodide (I–) from the water. PA-R4 was highlighted as an entirely biobased cationic polyamide as its precursors were Q-4ATA and the glucose diamine derivatives. It was calculated to have more than 99% use of renewable sources in the sustainability metric. With 120 min equilibrium time, more than 80% adsorption of 10 mg/L initial I– concentration in 90 °C was confirmed. The ability of our biopolyamides to perform stable anion-exchange processes in various conditions has made them a new, sustainable, and promising system for anionic pollution remediation in water.