Toward Non-Isocyanate Polyurethanes: Green Synthesis Routes and Recycling Technologies

Polyurethanes (PUs) are extensively utilized polymers known for their excellent properties. However, the conventional synthesis of PUs heavily depends on toxic isocyanates, creating significant environmental and health risks. To mitigate these issues, research has increasingly focused on synthesizing non-isocyanate polyurethanes (NIPUs). This review systematically discusses the primary green synthesis routes for NIPUs: (1) Bis(dialkyl carbonate) route, (2) Transurethanization route, (3) Cyclic carbonate route, and (4) Ring-opening polymerization (ROP) route. While PUs exhibit superior mechanical and chemical performance, their disposal at the end of life remains a major challenge. Currently, the main recovery methods include chemical degradation (or raw material recycling) and mechanical recycling, with chemical recycling offering potential for a closed-loop process. This review briefly summarizes these disposal strategies, aiming to encourage sustainable practices. It highlights recent advancements in green synthesis and recycling technologies, focusing on pathways for creating environmentally friendly and recyclable NIPUs. In light of increasing environmental and regulatory pressures to minimize the use of isocyanates due to their toxicity, this paper comprehensively reviews current advances and future prospects in the synthesis and recycling of NIPUs, focusing on sustainable and environmentally friendly approaches. The review delves into innovative synthesis methodologies for NIPUs, highlighting green pathways while also addressing challenges related to end-of-life polyurethane management, with a focus on advancements in chemical recycling technologies.