04 Oct Non-isocyanate polyurethane (NiPU) 

Replacing Toxic Isocyanates: The Emergence of Non-Isocyanate Polyurethane Materials

Non-isocyanate polyurethanes (NIPUs) represent a significant advancement in polymer materials, offering a safer and more sustainable alternative to traditional polyurethanes.   

Polyurethanes represent a significant class of polymer products. With an estimated annual market size of around 20 million tons, polyurethanes are primarily used in manufacturing rigid and flexible foams, as well as coatings or adhesives. These polymers are characterized by the presence of urethane (carbamate) linkages resulting from the addition reaction between a di- or polyisocyanate and a compound containing at least two hydroxyl groups (Figure 1). Nevertheless, due to the health risks linked to di- or polyisocyanates, extensive research has been dedicated for years to discovering safer alternatives. Addressing the toxicity issues associated with these materials is even more crucial given that the commercial production of isocyanates also relies on another toxic precursor, the phosgene. 

An innovative and promising method to eliminate the use of toxic isocyanates is the synthesis of polyhydroxyurethanes (PHUs), also known as non-isocyanate polyurethanes (NIPUs), by reacting poly-cyclic carbonates with poly-amines. Thermoplastic polyurethanes can be produced using precursors with a functionality of 2 (Figure 1), while thermosetting polyurethanes are formed with precursors of higher functionality. This method offers 100% atom economy and utilizes a diverse range of poly(cyclic carbonate) which can be easily synthesized via a straightforward [3+2] CO2 insertion into the corresponding epoxy precursor. This makes NIPU a highly efficient and eco-friendly alternative to conventional PU materials. 

Figure 1. Compared synthesis pathways of polyurethanes (PU) and non-isocyanate polyurethanes (NIPU) 

Cyclic carbonates to design NIPU materials 

Cyclic carbonates rapidly gained attention in both academic and industrial circles, thanks to their versatile and eco-friendly properties that align perfectly with the principles of green chemistry and sustainability. The most widely adopted and efficient method for producing cyclic carbonates, even on an industrial scale, is the cycloaddition of CO2 to epoxides. This process not only utilizes carbon dioxide – a renewable, non-toxic, and abundantly available resource – but also boasts 100% atom efficiency, ensuring that all reactants are fully incorporated into the final product. Plus, it can be executed effectively without the use of solvents (Figure 2), making it an ideal green chemistry solution (Figure 2).

Figure 2. Synthesis of cyclic carbonates from CO2 and epoxides and selected applications 

Cyclic carbonates have the ability to undergo ring-opening reactions with alcohols and amines, making them versatile reactants for various chemical syntheses. When reacting with primary and secondary amines, cyclic carbonates form hydroxyurethane groups. In the case of polyamines, this process results in the production of polyhydroxyurethanes, thus presenting a more eco-friendly alternative to traditional polyurethanes that rely on the reaction between toxic isocyanates and polyols. 

Depending on the specifications related to the targeted applications, it is essential to adjust the chemical composition of cyclic-carbonate/amine formulations. In this regard, SPECIFIC POLYMERS has been developing a catalog of cyclocarbonate compounds over the years, featuring various chemical structures and functionalities that allow the adjustment of material properties through formulation work. Our best-selling products are highlighted below and our full cyclocarbonate R&D product catalog can be downloaded from the link below.