Nonlinear Shear and Extensional Rheology of Telechelic Metallosupramolecular Networks

We investigate the nonlinear shear and extensional rheology of telechelic metallosupramolecular polymer networks in the melt state. Poly(n-butyl acrylate) (PnBA) star precursors with varying molecular spans (unentangled, barely entangled, and well-entangled) are end-linked through metal–ligand complexes with varying bond strengths (Zn2+, Cu2+, and mixtures). Linear viscoelastic properties are quantitatively described by using the Rouse model for short stars and a time-marching algorithm tube model for entangled stars. In nonlinear start-up shear, densely cross-linked networks obtained from the association of unentangled precursors exhibit pronounced shear hardening before reaching a maximum when stickers start dissociating. For these systems, a strong failure of the Cox–Merz rule is observed, in contrast to networks based on entangled precursors. In shear, the yielding strain, γmax, is found to be independent of the shear rate when sticker exchange is slow relative to deformation, indicating strain-controlled bond dissociation and an effective nonlinear sticker lifetime scaling as τsticker, NLVE ≈ γmax/γ̇. The maximum stretching ratio is a key parameter to rationalize transient behavior in both shear (λmax ≈ Nstrand1/2) and elongation (ϵH, max ≈ ln Nstrand1/2). Entanglements introduce additional dissipation through chain sliding, reducing strain hardening and enhancing network toughness.