Hybrid polyhydroxyurethanes: How to overcome limitations and reach cutting edge properties?

The restrictions on isocyanate substances have encouraged researchers to find alternative methods for the synthesis of Polyurethanes (PUs). New pathways have been designed with focus on non-hazardous and eco-friendly substances. The reaction of cyclic carbonates and amines has appeared as the most promising substitute for the synthesis of Non-Isocyanate Polyurethanes (NIPUs). The obtained Polyhydroxyurethanes (PHUs) have been deeply studied these last decades to offer the best solutions in the substitution of isocyanates in PUs synthesis. Strong efforts have been paid to understand key parameters for the synthesis of PHUs and to design new architectures. However, some limitations in terms of kinetics, conversion and molar masses still remain and impede PHUs expansion. Therefore, this review aims to detail the recent progress that has been made on a new strategy, the hybrid PHUs. The characteristics of additional reactants such as a high reactivity, a low viscosity or the ability to reach higher conversions can be combined with the properties of PHUs in hybrid networks. Other functional groups such as acrylates, methacrylates, epoxies, alkenes or siloxanes give access to new designs and materials with higher performances. Hence, the different strategies to perform hybrid PHUs are discussed and detailed. The main strategies employed are the co-polymerization in one-step, the synthesis of prepolymers with various architectures and the synthesis of organic/inorganic and composite PHUs. Furthermore, a short overview of reprocessable PHUs is given as another outlook for PHU development.