Bio-based routes to synthesize cyclic carbonates and polyamines precursors of non-isocyanate polyurethanes: A review

The synthesis of conventional polyurethanes (PUs) relies on isocyanate reactants as crucial starting materials. Toxicity, water-sensitivity and phosgene-based synthesis of isocyanates have made it necessary to undertake systematic and focused research to develop environment-friendly processes that use ecofriendly and non-hazardous materials. Among the numerous pathways that have been proposed, the reaction between cyclic carbonates and polyamines is shown to be the most promising route for the synthesis of non-isocyanates polyurethanes (NIPUs). The past decade has witnessed a consistent trend that seeks to take advantage of the vast reserve of renewable feedstocks such as vegetable oils, terpenes, lignin derivatives, and polyols as starting molecules for the synthesis of NIPU precursors. More recently, numerous strategies have come to the fore seeking to utilize the abovementioned renewable resources for the synthesis of NIPUs to meet the prerequisites of green chemistry. In this context, this review aims to shed light on recent progress that has been made in this direction. It also critically reviews the various green routes that have been pursued towards the synthesis of NIPU and their precursors to pave way for their applications in the PU industry. The challenges currently faced by industry in making use of these renewable (NIPUs and their precursors) materials into large-scale production is also highlighted.