Emerging Polyhydroxyurethanes as Sustainable Thermosets: A Structure-Property Relationship

Polyhydroxyurethanes(PHU), obtained from CO2-basedcyclic carbonates (CC) and polyamines, are known as greener and saferalternatives to conventional polyurethanes. Interestingly, the hydroxyurethanemoieties present along the PHU's backbone offer unexploredopportunities in terms of enhanced adhesion and mechanical propertiesthat could be a major breakthrough in many structural applications.Furthermore, PHUs have shown thermomechanical recyclability arisingfrom the ability of hydroxyurethane moieties to participate in reversibleexchange reactions. However, the relationship between the macromolecularstructure, the processability, and the final properties of these materialshave not been evaluated to a sufficient extent to establish a comprehensiveoverview of these emerging thermosets. In this sense, this work aimsto address this research gap by investigating the rheological andthermomechanical performances of PHU thermosets and opening an unexploreddoor for future sustainable engineered structural applications. Aspecial emphasis was put on PHU thermosets formulated using potentiallybiobased monomers. The rheological behavior during cross-linking ofthe PHU formulations was studied and highlighted the importance ofthe number of CC functionalities in the viscosity and gel time, rangingfrom 10 min to nearly 3 h. Moduli superior to 2 GPa and glass transitionover 50 degrees C were obtained for short multifunctional CC. Finally,the dynamic network behavior of these PHUs was also demonstrated throughstress-relaxation and reprocessing. High temperatures (over150 degrees C) and pressure lead to a good recovery of the thermomechanicalproperties. Such materials appear to be an interesting platform forstructural applications, particularly fiber-reinforced polymers, thatcan overcome many sustainability challenges.