Fast and Facile One-Pot One-Step Preparation of Nonisocyanate Polyurethane Hydrogels in Water at Room Temperature

Abstract

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 bulk, followed by their swelling in water. Their direct one-pot one-step synthesis in water is not possible because of the fast hydrolysis of isocyanates. The attractive greener variant for PU that consists of the polyaddition of poly(5-membered cyclic carbonate)s with polyamines is also suffering from a similar drawback (the hydrolysis of the cyclic carbonates), but also from the low reactivity of the reagents at room temperature. Herein, we report the first synthesis of PU hydrogels by a nonisocyanate route in water at room temperature from easily accessible CO2-sourced five-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 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 modulation of the mechanical properties of the hydrogel. This work opens up enormous perspectives in the design of elusive PU-based materials in water from largely accessible five-membered cyclic carbonates.