Tuning the mechanical and dynamic properties of imine bond crosslinked elastomeric vitrimers by manipulating the crosslinking degree

Vitrimers are a class of covalently crosslinked networks that act as a traditional thermoset at low temperatures while they can flow and act as a viscoelastic liquid at high temperatures through bond exchange reactions. The state-of-the-art approach to tune the mechanical and dynamic properties of vitrimers is to explore new exchangeable chemistries and alter catalyst systems and stoichiometric ratios of the starting materials. Herein, we initiate an alternative approach toward this goal. In particular, aldehyde group-terminated polybutadiene rubber (APB) with different molecular weights were prepared and subsequently crosslinked by tris(2-aminoethyl)amine through the formation of imine bond linkages. The modulus and ultimate strength of the imine bond crosslinked networks are consistently enhanced with the decrease of the molecular weight of APB precursors. In addition, APB with a higher molecular weight, i.e. a lower crosslinking degree, leads to a faster relaxation rate and a higher activation energy for network rearrangement. We envision that this work provides a methodology to tune the mechanical and dynamic properties of vitrimer materials by altering the precursor molecular weight and network crosslinking degree.