Volumetric and Rheological Properties of Vitrimers: A Hybrid Molecular Dynamics and Monte Carlo Simulation Study

Contrary to thermosets, vitrimers adjust their topology upon heating without loss of network integrity. Here, the proposed simulation methodology utilizes coarse-grained molecular dynamics in conjunction with a Monte Carlo method to capture the network integrity and flowability of vitrimers at high temperatures. The model vitrimer shows two transition temperatures. In addition to the conventional glass transition temperature, the topology freezing temperature is detected from the volumetric and rheological data. In the glassy state, the mobility of the vitrimer and thermoset is identical, whereas increasing the temperature results in a diffusive behavior in the vitrimer. The rheological data capture the main feature of vitrimers, which is the terminal regime of the elastic modulus at low frequencies. The zero-shear viscosity of the model vitrimer follows an Arrhenius-like temperature dependence at temperatures above the topology freezing temperature. The horizontal shift factors obtained from collapsing the rheological data onto master curves also display the same temperature dependence. Simulations reveal that the lifetime of the exchangeable bonds determines the rheology and dynamics of these networks. When the rate of the deformation is higher than the rate of the bond exchange, the system behaves as a typical thermoset, while at lower rates, the vitrimer behaves as a viscous liquid.