4. Pathways to isocyanate-free polyurethanes

Due to the toxicity of isocyanates, alternatives are being studied to synthesize polymers similar to conventional PUs without using isocyanates. Non-isocyanate PUs (NIPUs) have emerged in this context . Several synthetic routes exist, with cyclocarbonate aminolysis the most extensively studied, although other methods such as aziridine copolymerization with carbon dioxide and ring-opening polymerization of cyclic carbamates are also being considered (figure 12 ). Some of these methods still rely on toxic precursors, but safer approaches such as transurethanization and polyaddition between cyclic...