Rational Control of Viscoelastic Properties in Multicomponent Associative Polymer Networks

Abstract

We report here the formation and dynamic mechanical properties of metallo-supramolecular networks formed by mixtures of bis-Pd(II) and Pt(II) cross-linkers with poly(4-vinylpyridine) in DMSO. Precise control over the dynamic mechanical properties of the bulk materials is achieved through the dissociation kinetics of the metal-ligand coordination bond responsible for cross-linking, the density of the cross-links, and the relative amounts of multiple cross-links. In networks formed from multiple types of cross-linkers, discrete contributions from each type of cross-linker are evident in the bulk mechanical properties, rather than an average of the contributing species. The heterogeneous rheology is consistent with simple models, to the extent that complex viscoelastic responses can be rationally engineered.

Manipulation of hydrogel assembly and growth factor delivery via the use of peptide–polysaccharide interactions

“…6, may be attributed to the multicomponent nature of the cross-linking in these systems, as both LMWH-LMWH and PF4 ZIP -LMWH interactions determine the rheological character of the gels. The resistance to flow in hydrogels is determined by the slower crosslinkers [66], and in SPR experiments. In SPR experiments, the LMWH-LMWH interactions are suggested to be much slower than PF4 ZIP -LMWH interactions (data not shown).…”

Model Transient Networks from Strongly Hydrogen-Bonded Polymers

“…In an early series of papers, Stadler and Freitas 11,[22][23][24] studied the rheological behavior of polybutadienes lightly modified with double-hydrogen-bonding phenylurazole groups, finding that even with light substitution along the backbone the storage modulus plateau was broadened and shifted to lower frequencies (although the overall network properties were primarily dictated by the highly entangled polymer backbone and the crystallization of the phenyl urazole side chains). More recently, reversible networks based on metal-ligand coordination have been synthesized and the macroscopic material properties directly related to the coordination dynamics; [25][26][27][28] in this case it was found that formation of a strong network required not just a high association constant but also slow dynamics of the reversible bond. Additionally, supramolecular gels based on hydrogen bonding in ionic liquids have been demonstrated and their rheological properties related to the strength and number of hydrogen bonds as well as stoichiometry of donor and acceptor units.…”

Thermoreversible associating polymer networks. I. Interplay of thermodynamics, chemical kinetics, and polymer physics

“…Most experimental systems seem to be kinetically limited, and this is the case treated by almost all published analytic theories for reversibly associating networks, including transient network models [22,25]. Theories for kinetically limited AP networks [20,21,24,26,27] assume that the sticky bond lifetime τ sb is so long compared to all "polymeric" relaxation times that it controls all important time scales for network relaxation, and therefore that kinetics only affect key network relaxation times through their effect on τ sb (or, alternately, as suggested by recent experiments [50,51], the inverse dissociation rate constant k −1 b , defined below). We show that the validity of this assumpton is questionable, and that there is a wide parameter space, plausibly accessible in experiments, where it is invalid.…”