Defect-controlled softness, diffusive permeability, and mesh-topology of metallo-supramolecular hydrogels

Nicolella, Paola; Koziol, Martha; Löser, Lucas; Saalwächter, Kay; Ahmadi, Mostafa; Seiffert, Sebastian

doi:10.1039/d1sm01456k

Cited by 18 publications

(26 citation statements)

References 41 publications

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“…This difference factor of 50 not only demonstrates the significant role of misconnectivities in supramolecular polymer systems based on short linear precursors but also highlights the fact that not all current PDCA ligands and Co 2+ ions are engaged in the formation of bis-complexes. 42,71 As such, we expect a low equilibrium constant, K, despite the very large dissociation rate constant, k d , for the complex formed by Co 2+ . To provide a rough estimate of the dissociation time, we fit the dynamic moduli curves obtained at 25 °C by considering two relaxation modes, each represented by a log−normal distribution of relaxation times at the high-and low-frequency ranges, as explained in the Supporting Information.…”

Section: Resultsmentioning

confidence: 92%

pH-Responsive Gelation in Metallo-Supramolecular Polymers Based on the Protic Pyridinedicarboxamide Ligand

et al. 2022

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Pyridinedicarboxamide (PDCA) ligands have been widely integrated into different polymer chemistries and provided promising self-healing properties in bulk upon adding specific metal ions. However, their application in the development of synthetic hydrogels is limited due to the lack of clear kinetics and thermodynamic data. To fill this gap, we study the dynamics of polymer hydrogels formed by the condensation of linear poly-(ethylene glycol) (PEG) precursors and the PDCA ligand, followed by the complexation with different metal ions at various pH values. Rheological studies reveal an unprecedented ability of PDCA in complexation with Co 2+/3+ and Ni 2+ at elevated pH values, but in contrast with former reports, not with Fe 3+ and Zn 2+ . Moreover, Co 2+/3+ gels demonstrate lower equilibrium constants resulting in faster and more efficient self-healing compared to those made by Ni 2+ . Spectroscopic UV and Fourier transform infrared (FTIR) studies also suggest structural modifications in the presence of the gel-forming metal ions but not the others. To explain these results, we employ static and periodic density functional theory (DFT) simulations. Static DFT indeed reveals that the binding interaction is clearly stronger for Co and Ni, and Fe shows the poorest values by far. The most stable complex geometry is octahedral, in which the central pyridyl, one lateral deprotonated amide, and one carbonyl participate in the metal coordination. Moreover, the periodic calculations unveil an overstabilization effect due to the noncovalent interactions between the PEG segments, which results in their torsion and formation of a helicoidal-like structure.

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Section: Resultsmentioning

confidence: 92%

pH-Responsive Gelation in Metallo-Supramolecular Polymers Based on the Protic Pyridinedicarboxamide Ligand

et al. 2022

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“…These data were evaluated similar to Lange et al ., except for some relevant procedural differences that will be explained below. Comparable data analysis was also applied on other tetra-arm star polymer systems. , Typically, three types of connectivities can be distinguished differing sufficiently in their RDC as shown in Scheme (SL, DL, and HOCs). This three-component fit was assumed to be a proper modeling choice for our system since the chemical and steric differences between PEG and PCL chains are small (see Table S3) and because all elastic strands contain a PCL and a PEG block that are under the same tension.…”

Section: Methodsmentioning

confidence: 99%

Amphiphilic Model Networks Based on PEG and PCL Tetra-arm Star Polymers with Complementary Reactivity

et al. 2022

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A new approach for the synthesis of model amphiphilic polymer co-networks (ACNs) based on a heterocomplementary coupling reaction of a 2-(4-nitrophenyl)-benzoxazinone terminated tetra-arm polycaprolactone star (tetra-PCL) with an amino-terminated tetra-arm polyethylene glycol star (tetra-PEG) is presented. The reaction conditions (solvent, concentration, and temperature) were varied widely. Reaction kinetics and gelation were analyzed with high-resolution NMR spectroscopy and computer simulations. The results agree with a nearly homogeneous mixture where local composition fluctuations affect kinetics only after most of the molecules are attached to the gel. Viscometry, dynamic light scattering data, and literature data for the solubility parameters were combined to provide estimates for the Flory−Huggins interaction parameter of the two star polymers in toluene, chloroform, and THF as solvents. These estimates allow one to collapse equilibrium swelling data in different solvents on a universal curve. Multiple quantum NMR analysis shows an enhanced formation of double connections between the same pair of stars as compared to preceding work on tetra-PEG gels made by the same cross-linking strategy but with a different coupling reaction. Besides this last observation, the remaining results indicate that the networks possess a near model-like structure with only a small fraction of pending arms as the most relevant type of network defects.

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“…Therefore, the model should be also useful in explaining the variation of network defects as a function of complex composition. 36,45 Analysis of the data in Figure S6 probably explains why the model fails to capture the loss of percolation in Co 2+ -rich samples at [EPh]/[M 2+ ] = 1.5. The model only considers the junctions in the percolated network and those residing in an isolated cluster do not contribute to the modulus.…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, under metal-poor conditions, as for [EPh]/[M 2+ ] = 3, the contribution of threefold chains shows an overshoot along with the relaxation process, as expected. Therefore, the model should be also useful in explaining the variation of network defects as a function of complex composition. , …”

Section: Resultsmentioning

confidence: 99%

Network Percolation in Transient Polymer Networks with Temporal Hierarchy of Energy Dissipation

2022

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Transient polymer networks with a temporal hierarchy of energy dissipation have advantages in many applications, ranging from injectable hydrogels to self-healing materials. However, their structure and rheology are often estimated based on their permanent network equivalents. To account for this, we extend the mean-field Miller–Macosko’s recursive model to predict the network percolation in metallo-supramolecular polymer networks. Moreover, a simple thermodynamic model is developed to predict the composition of metal complexes with different coordination geometries in a multi-component network. To challenge the theoretical framework with experiments, we form model network hydrogels upon the coordination of phenanthroline-functionalized tetra-arm poly(ethylene glycol) (tetraEPh) with a mixture of Co2+ and Fe2+ metal ions, which are proved to expose different coordination geometry preferences. We demonstrate that even small deviations in the stoichiometric ratio of ligand to metal ions or variation of the coordination geometry preference significantly changes the network structure, which results in remarkably different macroscopic properties compared to those of the equivalent permanent networks. The theoretical model can explain the variation of the lifetime and relative contributions of the fast and slow relaxation modes in the shear modulus at various metal ion compositions. Moreover, the model explains that the significant drop in the modulus in the presence of excessive metal ions is due to the profound formation of threefold connected polymer precursors. The developed theory forms a reliable framework for predicting the time evolution of the junction composition, network percolation, and defect formation in transient polymer networks.

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Defect-controlled softness, diffusive permeability, and mesh-topology of metallo-supramolecular hydrogels

Abstract: In a model 4-arm pEG supramolecular network, connectivity defects are systematically introduced with different ratios of 8-arm pEG, resulting in intra-molecular loops, and providing a softer polymer network and higher self-diffusion coefficients.

Cited by 18 publications

References 41 publications

pH-Responsive Gelation in Metallo-Supramolecular Polymers Based on the Protic Pyridinedicarboxamide Ligand

pH-Responsive Gelation in Metallo-Supramolecular Polymers Based on the Protic Pyridinedicarboxamide Ligand

Amphiphilic Model Networks Based on PEG and PCL Tetra-arm Star Polymers with Complementary Reactivity

Network Percolation in Transient Polymer Networks with Temporal Hierarchy of Energy Dissipation

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