Fast and facile one-pot one-step preparation of non-isocyanate polyurethane hydrogels in water at room temperature

Since the discovery of polyurethanes (PU) by Otto Bayer in 1937, PU hydrogels are still commonly produced by the polyaddition of nasty and toxic polyisocyanates with polyols in organic solvents or in the bulk, followed by their swelling in water. Their direct one-pot one-step synthesis in water is not possible due to the fast hydrolysis of isocyanates. The attractive greener variant for PU that consists in the polyaddition of poly(5-membered cyclic carbonate)s with polyamines is also suffering for a similar drawback (the hydrolysis of the cyclic carbonates), but also for the low reactivity of the reagents at room temperature. Herein, we report the first synthesis of PU hydrogels by a non-isocyanate route in water at room temperature from easily accessible CO2-sourced 5-membered cyclic carbonates (5CCs) and a commercially available polyamine. We demonstrate that PU hydrogels are now formed with impressive short gel times (15-20 min) provided that the pH is adjusted in the 10.5-11.5 range in order to limit 5CCs hydrolysis. Hydrogels of good mechanical properties and high swelling ability are prepared in a facile one-pot process. The robustness of the process is also illustrated by dispersing clays (natural or synthetic) or a natural hydrosoluble polymer (gelatin) in the formulation. These additives do not perturb the polymerization and enable to modulate the mechanical properties of the hydrogel. This works opens enormous perspectives in the design of elusive PU-based materials in water from largely accessible 5- membered cyclic carbonates.