Non-isocyanate polyureas are an environmentally and health-conscious alternative to conventional polyureas as they eliminate the use of toxic isocyanate monomers. A research team has now developed a solvent-free melt polycondensation process combining bio-sourceable urea with linear primary diamines and aromatic diamines. This approach enables the direct incorporation of aromatic diamines – a step that has proven challenging in earlier non-isocyanate routes. By adjusting the aromatic diamine content (5–20 wt%), the researchers created polyureas with high thermal stability (decomposition temperature Td,5 % > 318 °C) and a wide range of mechanical properties. The study demonstrates that high-performance, semi-aromatic polyureas with tunable properties can be produced using greener synthesis methods without compromising performance.