(611e) Kinetics Pathway Complexity of Supramolecular Block Copolymer Self-Assemblies

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 reflect the impact of dynamic/reversible bonds on the free energy landscape during structure transitions. In this study, by focusing on the disorder-order transition of supramolecular diblock copolymers (SDBC), we show that the self-assembly of SDBC exhibits significantly greater kinetic pathway complexity comparing to their covalent analogue in direct dynamics simulations. The complexity is characterized by appearances of a rich family of long-lived intermediate morphologies. Free energies of the intermediate morphologies and the minimum free energy paths that connect these morphologies to the equilibrium state are then constructed to provide understanding about the thermodynamic nature of these morphologies. It is found that the long-lived intermediate morphologies are the metastable states in the free-energy landscape, locally stabilized by free energy barriers that separate them from the equilibrium state. These local free energy minima are created by balancing the segregation and association of the immiscible polymer building blocks, offering kinetic pathways that are not accessible to covalent diblock copolymers. We hence conclude that kinetic pathway complexity exhibited by SDBC self-assemblies derives directly from the reversibility of the supramolecular bonds. We expect this finding applies to SBC self-assemblies in general.