Polyurethanes are one of the most versatile families of polymers and are one of the most widely used in thermosets. Due to their static cross-linked structure, they have limited capacity to be reprocessed, recycled or reshaped and therefore once these materials suffer any damage, they are typically discarded. One of the key features of polyurethanes is given by the dynamic behavior of the urethane group at high temperatures, especially in the presence of an appropriate catalyst. In this work a detailed study is performed to demonstrate the dynamic nature of aliphatic and aromatic polyurethanes in the presence of different catalysts. Our study shows that the dynamic behavior is highly dependent on the nature of the isocyanate, the urethane/free alcohol ratio and the nature of the catalyst that is used in the polymerization. We found that the stress relaxation of polyurethane thermosets in the absence of a catalyst is related to the degradation of the network and that the catalyst plays a pivotal role in enhancing the dynamic behavior prior to degradation, especially in aromatic polyurethanes. In fact, the organocatalyst p-toluensulfonic acid (PTSA) is shown to have the ability to enhance the dynamic behavior via hydroxyl mediated transcarbamoylation (associative mechanism) whereas dibutyltin dilaurate (DBTDL) catalyzes transcarbamoylation reactions via both associative and dissociative exchange mechanisms at temperatures as low as 120 °C. These results have been confirmed by model reactions performed with low molecular weight compounds. We believe that this work offers a significant insight into the influence of structural parameters and catalyst effects in the intrinsic dynamic behavior of polyurethanes, and moreover, provides new alternatives to selectively enhance the dynamic nature of polyurethanes.

The importance of systematic and efficient recycling of all forms of plastic is no longer a matter for debate. Constituting the sixth most produced polymer family worldwide, polyurethanes, which are used in a broad variety of applications (buildings, electronics, adhesives, sealants, etc.), are particularly important to recycle. In this study, polyurethanes are selectively recycled to obtain high value-added molecules. It is demonstrated that depolymerization reactions performed with secondary amines selectively cleave the C-O bond of the urethane group, while primary amines unselectively break C-O and C-N bonds. The selective cleavage of C-O bonds, catalyzed by an acid:base mixture, led to the initial polyol and a functional diurea in several hours to a few minutes for both model polyurethanes and commercial polyurethane foams. Different secondary amines were employed as nucleophiles to synthesize a small library of diureas obtained in good to excellent yields. This study not only targets the recovery of the initial polyol but also aims to form new diureas which are useful building blocks for the polymerization of innovative materials.