Investigation of Templated Entanglements in Polymer Networks via Small-Angle Scattering Techniques

Recent work established the viability of a supramolecular template approach to control the formation of trapped entanglements in polymer networks. However, characterization of the entangled networks has been limited to swelling and rheometry. Small-angle neutron and X-ray scattering techniques (SANS and SAXS, respectively) provide complementary ways to probe the size and conformation of polymer chains within the networks. Herein, we examine gels with trapped entanglements templated by bis(phenanthroline)copper(I) complexes via SANS and SAXS and compare the results against isomeric controls without templated entanglements. When the gels are swollen in deuterium oxide (D 2 O), a peak is observed in all cases at ∼0.08 Å –1 in both SANS and SAXS patterns, indicative of phenanthroline aggregation into scattering clusters. Tensile testing conducted with in situ SANS measurements of all the gels─with the bis(phenanthroline)copper(I) complexes intact and with the copper removed─revealed that templated entanglements prevent stress-induced dispersion of the scattering clusters in the copper-containing gels. Thus, this work illuminates how templated entanglements impact the stress response of metallogels and demonstrates the power of scattering techniques to characterize these elusive topological features of polymer networks.