Non-isocyanate polyurethanes: from chemistry to applications

Conventional polyurethanes involve the use of isocyanates, which require hazardous and toxic phosgene for their manufacture. These monomers cannot be manufactured without elaborate safety devices and huge investment. Isocyanates are also considerably toxic and moisture sensitive. Growing global awareness of the need to protect our environment and continually strive to ensure the safety, health and well-being of those in the industry and consumers has created a demand for environment-friendly products. The cyclic carbonate-primary amine addition reaction which results in hydroxyurethanes is a unique reaction and has been extensively studied over the last few years. This chemistry is now attracting research interest due to its potential application in the preparation of "green'', non-porous, moisture-insensitive, isocyanate free polyurethanes. This review focuses on catalysis, the mechanism involved in the formation of Non-Isocyanate Polyurethanes (NIPU) from five-membered cyclic carbonates and the reaction kinetics for their synthesis. The higher homologues of the cyclic carbonate family, the six-membered cyclic carbonates, are similar to, but more reactive than, the five-membered cyclic carbonates and can also serve as a source for production of isocyanate free polyurethanes. This review also summarizes various application of NIPU in coatings, composites, construction and biochemical fields.