Sustainable isocyanate-free polyurethanes

Polyurethanes (PUs) are among the most important polymers, with an annual production of more than 18 millions of tons, about 5 mass % of total worldwide polymer production. They are very versatile polymers, as they can be thermoplastic, elastomeric, thermoset and foams. They are suitable for a large variety of applications and, among them, as materials for cars. PU are formed by the reaction between polyols and isocyanates. Isocyanates present concerns from the point of view of their impact on environment, health and safety. They are produced from the reaction of amines with phosgene and have several potential negative effects on the human health. The present work is based on the synthesis of isocyanate free-polyurethanes. Various strategies were adopted, such as: (i) Ring Opening Polymerization (ROP) of cyclic carbamates prepared via dialkyl carbonate chemistry. (ii) Ring Opening of cyclic carbonates by amines The ROP of cyclic carbamates was carried out in the presence of boron trifluoride diethyl etherate as it resulted the most active catalyst. The process is solvent-free, chlorine-free and no by-products are produced. Furthermore, oligomers obtained with this procedure were modified at the chain end reaction with the biobased molecule 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (SP). The so-formed PU-SP oligomers were used to prepare adducts with carbon nanotubes (CNT). The stability of the suspensions in ethyl acetate was observed and high-resolution transmission electron microscopy (HRTEM) micrographs showed that the PU oligomers are wrapped around the nanotubes.