Stress-induced dynamics in glassy vitrimers

Vitrimers are a class of polymers that bring together desirable mechanical properties of thermosets with the recyclability of thermoplastics. This ability arises from the rearrangement of the vitrimer network via a bond shuffling mechanism while its cross-link density remains preserved. As the properties of the material are directly affected by the dynamics of the polymer chains, it is critical to understand the link between the macroscopic behavior and the microscopic dynamic of the molecules. Molecular dynamics simulations can provide detailed molecular mechanisms of the system under macroscopic stress-induced deformations. We present a simulation methodology that utilizes coarse-grained molecular dynamics in conjunction with a Monte-Carlo method to capture the bond exchange in vitrimers. Constant stress is applied to the system below its glass transition temperature while monitoring the strain (e.g., creep). Vitrimer shows accelerated dynamics under applied shear stress compared to that of thermoset. This different behavior between the two networks is reflected in the mean squared displacement of the crosslinker. In addition, the motion of the crosslinker shows non-affine displacement, resulting in regions of enhanced mobility (e.g., dynamic heterogeneities).