Fig. 8. (a) Stress relaxation of vitrimers and vitrimer nanocomposites: neat matrix (blue), filled with epoxide-functionalised fillers (covalently bond) and non-functionalised silica particles (non-covalently bond). Schematic representation of interfacial exchange reactions of covalently bound fillers. Adapted with permission from ref. 82. Copyright 2016 American Chemical Society. (b) Stress relaxation of filled vitrimer nanocomposites with a different ratio of covalently bound fillers, resulting in different cross-link density and relaxation behaviour (from the least (EC10) to the highest cross-linked network (EC30)). Adapted with permission from ref. 84. Copyright 2018 American Chemical Society.