Molecular Examination of Healable Polymers with Covalent Adaptive Networks

Fatigue remains the primary culprit for failure in various composite systems despite years of research. Usually, nano-scale additives are added to materials to improve fatigue performance; although these materials can prolong the life-cycle through various toughening mechanisms to resist fracture, failure is not averted. Other approaches have explored self-healing polymers that release a curing agent to repair local damage through embedded particles or vascular systems, but these are limited to a few cycles of healing. Polymers with a dynamic covalent adaptive network (CAN) have shown immense promise to address these challenges. We present a study on such CAN polymeric system, which can heal through topological rearrangement of the polymeric network through a transesterification reaction. Guided by experiments, we examine the network evolution using reactive molecular dynamics (ReaxFF) during the exchange reactions that lead to healing in CANs. Since the kinetics of such reactions is slow, we used Accelerated ReaxFF for this study; Accelerated ReaxFF can speed up reactions at low temperatures by providing extra energy to the reactive sites, which helps mitigate potential side reactions due to high temperatures. Our results show the network evolution plays a pivotal role in retained mechanical properties.