Thermal and viscoelastic properties of entangled supramolecular polymer networks as a powerful tool for prediction of their microstructure

Thermal and viscoelastic properties of entangled supramolecular polymer networks, SPNs, depend strongly on binary and collective assembly of associative groups. The collective assemblies can phase separate from polymer matrix chains and form domains with different sizes and shapes, which have different melting point transitions. By increasing content of associative groups along the polymer chains, their high-order association leads to formation of domains, which have higher melting temperatures than other ones. We prepared a SPN system that contains three networks. All networks have similar precursor polymer backbone, but different content of ureidopyrimidinone, UPy, moiety as strong hydrogen bonding associative group. Thermal and viscoelastic properties of these networks were studied by differential scanning calorimetry and dynamic mechanical thermal analysis measurements. Binary-associated UPy groups phase separate into collective assemblies by pi-pi stacking. These stacks melt at different temperatures upon heating. The presence of transient assemblies is considerably hinder the relaxation of polymer backbone chains. These domains can be observed in the microstructure of networks by optical microscopy. Thermal and viscoelastic properties of sample with highest content of UPy groups are significantly different from the other networks. This is related to the high-order association of UPy motifs, as can be captured by presence of needle-like domains in its microstructure.