A direct comparison of the thermal reprocessing potential of associative and dissociative reversible bonds in thermosets

Abstract

This study compares the thermal reprocessing potential of thermosets comprising associative or dissociative dynamic covalent bonds by evaluating their rheological behavior. In correspondence with earlier studies, it is shown that the dynamic behavior upon the application of a thermal stimulus is highly dependent on the selected molecular mechanisms. However, so far it has been difficult to unambiguously determine the effect of the type of reversible molecular mechanism on the reprocessing potential due to the significant dissimilarity of backbones within different thermosets. To overcome this hurdle, we designed and synthesized special model thermoset systems with near-identical backbones. This made it possible to assess the thermal reprocessing potential of these mechanisms directly and in a quantitative manner. A vinylogous urethane-based linkage and a Diels–Alder (DA) linkage were selected as the model associative and dissociative dynamic mechanisms, respectively. These linkages were embedded in comparable molecular structures, polymerized and subjected to near-identical processing conditions. The results show that the viscosity of a thermoset containing dissociative linkages can be severely reduced by applying heat, which could allow for more facile mechanical recycling via conventional thermoplastic processing methods. A similar impact on the viscosity was not observed in the associative thermoset prepared in this work and therefore the thermal reprocessing potential of this material is currently limited compared to its dissociative counterpart.