Structure and Dynamics of a Bisurea-Based Supramolecular Polymer in n-Dodecane

The structure and dynamics of a supramolecular polymer formed by a bisurea-type compound, 2,4-bis(2-ethylhexylureido)toluene (EHUT), in an apolar solvent, n-dodecane (C₁₂), were examined in detail. The EHUT/C₁₂ organo-gel system forms long, dynamic chain-like supramolecular polymers, which lead to an entangled network showing remarkable viscoelastic behavior with two major relaxation modes. A slow relaxation mode with an approximately constant relaxation time, τ_S, was observed in a flow region and the other, fast, relaxation mode with a time τ_F1 (<τ_S) was observed in a high-frequency range. Because no dielectric relaxation behavior was observed over a frequency region including the mechanical τ_S and τ_F1 relaxation modes, the formed supramolecular polymer does not possess any total dipole moment due to antiparallel intermolecular hydrogen bonding of the two ureido groups of each EHUT unit. A structural model for the supramolecular polymer formed in EHUT/C₁₂ is proposed based on force-field simulations. This proposed model is consistent with all the experimental data concerning this system: flow birefringence measurements, dielectric spectroscopy, SANS, and FTIR.