Temperature-Dependent Structural Transition in Hydrogen-Bonded Supramolecular Polymers Using Coarse-Grained Simulations

Hydrogen-bonded supramolecular polymers exhibit a unique combination of structural, thermodynamic, and dynamic properties due to their reversible, noncovalent monomer associations. However, the precise mechanism underlying this process remains elusive. In this work, we focus on the supramolecular polymerization of 2,4-bis(2-ethylhexylureido)toluene (EHUT), which self-assembles into filament and tube structures in the nonpolar solvent cyclohexane via hydrogen bonding under ambient pressure and controlled temperatures. To investigate this temperature-dependent self-assembly behavior, we developed a transferable coarse-grained model that allows the study of EHUT supramolecular polymerization in cyclohexane. Here, we mimic temperature-dependent hydrogen bonding by tuning dipole parameters in the model by exploiting the fact that local dipole interactions dominate the hydrogen bonding. Molecular dynamics simulations based on this model successfully reproduce both filament and tube structures over a range of temperatures. We further investigated the kinetics and underlying mechanisms of EHUT self-assembly based on these simulations. The results reveal a stepwise and cooperative polymerization mechanism for the formation of filaments and tubes, respectively. This study offers a multiscale spatiotemporal characterization of EHUT self-assembly in cyclohexane and introduces a hydrogen-bond-driven coarse-grained modeling approach that can be extended to other temperature-dependent supramolecular systems.