Viscoelastic\nProperties of Metallo-Supramolecular\nNetworks: Relationship Between Sticker/Entanglement Dynamics and Terminal\nRelaxation

We investigate the linear viscoelastic properties of\npoly(<i>n</i>-butyl acrylate) (PnBA) metallo-supramolecular\nnetworks\nin the melt state, based on bis-complexes formed by terpyridine (tpy)\nligands and divalent metal ions. These networks are constructed from\ntelechelic stars, entangled or not, bearing tpy chain-ends. The nature\nof the metal ions is varied (Zn(II) and Cu(II) ions, blended or not)\nas well as the used amount (stoichiometric amount or excess). By systematically\nvarying the network composition (building block architecture and ion\ncontent), we elucidate the influence of stickers on terminal relaxation\nwith a focus on the interplay between sticker and entanglement dynamics.\nThe delayed terminal relaxation of the transient networks is rationalized\nby the means of modified Rouse and time-marching algorithm (TMA) tube\nmodels. Our theoretical analysis supports a multistep relaxation mechanism\ninvolving repeated dissociation/reassociation events. It also allows\nus to extract an intrinsic value of approximately 40 kJ/mol for the\nactivation energy for the dissociation of Zn<sup>2+</sup>/tpy bis-complexes,\nregardless of the building block topology or the ion content. In the\npresence of entanglements, this activation energy cannot be found\nby only looking at the temperature dependence of the terminal relaxation\ntime, which demonstrates the importance of separating the sticker\nand entanglement dynamics to unravel the viscoelastic response of\nthese transient networks.