Metalation/De-metalation as a Post-Gelation Strategy to Tune the Mechanical Properties of Catenane-Crosslinked Gels

Abstract

Mechanically interlocked molecules (MIMs) possess unique architectures and non-traditional degrees of freedom that arise from well-defined topologies that are achieved through precise mechanical bonding. Incorporation of MIMs into materials can thus provide an avenue to discover new and emergent macroscale properties. Here, the synthesis of a phenanthroline-based [2]catenane crosslinker and its incorporation into polyacrylate organogels is described. Specifically, Cu(I) metalation and de-metalation was used as a post-gelation strategy to tune the mechanical properties of a gel by controlling the conformational motions of integrated MIMs. The organogels were prepared via thermally initiated free radical polymerization, and Cu(I) metal was added in MeOH to pre-treated, swollen gels. De-metalation of the gels was achieved by adding cyanide salts and washing the gels. Changes in Young’s and shear moduli, as well as tensile strength, were quantified through oscillatory shear rheology and tensile testing. The reported approach provides a general method for post-gelation tuning of mechanical properties using metals and well-defined catenane topologies as part of a network architecture.

Doubly Threaded Slide-Ring Polycatenane Networks

“…Figure 1c is a schematic of a poly [2]catenane network in which the crosslinking unit is a [2]catenane (two interlocked rings) moiety. 35,36 The presence of these [2]catenane crosslinks imbues the networks with increased mobility derived from the elongation, rotation, and twisting (arrows, Figure 1c) of the interlocked rings relative to the same network without the catenane moieties. As with the SRNs, the mobility elements introduced by the nature of the interlocked architecture impact the properties of the network.…”