Defects as a Highway to Stress Relaxation of Vitrimers

Vitrimers are a promising class of plastics made by disordered networks of polymers. They are an ideal recyclable material being both strong and malleable, because unlike common plastics, vitrimers can swap their bonds without breaking. The swap mechanism also grants them exceptionally versatile properties ranging from self-healing to responsiveness to chemical and physical stimuli. Understanding how the mechanics of vitrimers follow from such bond-swap dynamics is a key physical question that we address using a new coarse-grained MD model which captures the essence of the bond dynamics while being insensitive to other chemical details. Our results reveal a dramatic dependence of their malleability on the number of polymer chains that loop back onto themselves. This highlights the importance of choosing the right building blocks for these new materials, as choices concerning polymer architecture have immediate implications for the number of such loops. Our work thus provides new guidelines for designing and developing these remarkable plastics. [1] Ciarella et al., PRL 2018.