Effects of dynamic bonds on the kinetic pathways of the disorder-order transition of supramolecular diblock copolymers

Supramolecular block copolymers (SBC) consist of covalent polymer building blocks that are connected into well-defined architectures via supramolecular bonds. Assisted by the dynamic and reversible supramolecular interactions, it is envisaged that SBC self-assemblies may exhibit more diverse morphologies, stimuli-responsivity and dramatically reduced annealing times/temperatures comparing to their covalent analogues. At the fundamental level, these features are related to the free-energy landscape of self-assemblies. It is therefore of central importance to understand the impact of dynamic/reversible bonds on the free energy landscape during structure transitions. In this study, we first conduct direct dynamics simulations to compare the kinetics of the disorder-order transition (DOT) of supramolecular diblock copolymers (SDBC) to that of covalent diblock copolymers (CDBC). We show that intermediate plateau in the structure order parameter is observed for both systems during the transition, and the length of plateau is shorter for SDBC. The observation indicates the presence of free-energy barriers in DOT, the magnitude of which is affected by the reversible bonds. Next, we apply the string method to construct the minimum free energy path of the transition, from which the transition state and the free energy barrier are evaluated. We show that the transition states are similar between SDBC and CDBC, but the free energy barrier associated with the DOT in SDBC is lower than that in CDBC.