Landscape of Network Connectivity in Transient Polymer Networks with Competing Homo- and Hetero-complementary Bonds

Abstract

Polymer networks expose a wide range of mechanical properties depending on their microstructure and connectivity. Specifically, transient networks based on end-linking of mixed telechelic polymer precursors capable of forming competing homo- and hetero-complementary bonds demonstrate a wide range of network structures and consequently mechanical properties depending on the composition and reactivity of employed precursors. To address this gap, the Miller–Macosko’s recursive model is extended to tetra-arm polymer precursors capable of forming homo- and hetero-complementary bonds. As such, the composition and time evolution of n-fold network connectivities are visualized as a function of precursor composition and bond selectivity. The model potential is highlighted by confronting its predictions with the rheological behavior of transient metallo-supramolecular polymer networks (MSPNs) obtained by mixing tetra-arm poly(ethylene glycol) functionalized with either sterically demanding mesitylene-substituted phenanthroline or unsubstituted slim phenanthroline or terpyridine ligands. The former precursor is incapable of homoleptic complexation; however, in combination with the latter two, they can form a mixture of homo- and heteroleptic complexes, depending on the coordination geometry preference of the utilized metal ion. These results not only visualize the connectivity landscape that can be explored in transient polymer networks, even beyond MSPNs, but can also provide a selectivity index for competing transient bonds based on rheological properties.