Deconvolution of the Effects of Binary Associations and Collective Assemblies on the Rheological Properties of Entangled Side-Chain Supramolecular Polymer Networks

The properties and function of supramolecular polymer networks are determined not only by pairwise interchain transient associations but also by chain entanglement and nanoscopic phase separation of the associative groups. To unravel the impact and interplay of these different factors, we devise a set of model supramolecular polymer networks in which the number of entanglements and the density of associative groups are systematically varied. Rheological data show that by increasing the density of associative groups, the plateau modulus grows to a steady level and extends over a distinct frequency range. This is credited to the presence of binary associations with unique partner exchange time. For samples where the high-frequency plateau stays at the constant level, a second plateau emerges at low frequencies in addition. This plateau, which is well below the entanglement plateau of the precursor, is attributed to the presence of collective assemblies of nanophase-separated associative groups, as confirmed by FTIR spectroscopy. The contributions of these two different levels of interchain associations are decoupled on the basis of a tube-based model. The obtained model parameters show that by increasing the number of network junctions, including both interchain associations and entanglements, the fraction of binary associations decreases, while the density of collective ones approaches a constant level.