Backbone Polarity Tunes Sticker Clustering in Hydrogen-Bonded Supramolecular Polymer Networks

Abstract

Many of the fascinating properties of natural materials emerge upon phase separation and clustering. However, biomimetic polymeric materials often demonstrate limited performances due to ignoring that hierarchy. Thus, there is a need to change the design paradigm from the simple integration of transient bonds to the engineering of structural hierarchy. To account for that, we develop an entangled hydrogen-bonded supramolecular polymer network, based on strong fourfold hydrogen-bonding ureidopyrimidinone (UPy) groups and poly(n-butyl acrylate) chains, where the local polarity is systematically varied by incorporating free hydroxyl (OH) groups. The integration of UPy groups significantly changes the relaxation spectrum, from a standard Maxwellian terminal flow to a high-frequency plateau spanning over three decades and the emergence of an additional lowfrequency plateau. The absence of first-order thermal transitions in DSC curves and the emergence of diffraction peaks at nanometer lengths in SAXS profiles imply the presence of unordered aggregates. The introduction of free OH groups, however, gradually removes the plateau at low frequencies and increases the high-frequency one. A basic tube-based model including the sticky Rouse and the contour length fluctuations that are hindered by a mean-field penalty is developed to explain relaxation steps of entangled chains in the presence of binary associations and their clustering. The obtained fit parameters provide a precious quantitative correlation between the structural characteristics and key material functions. Specifically, despite the UPy content increases the penalty of chain dynamics, the fraction of OH groups does not, due to the countereffects of promoting binary associations and reducing clustering.

Polyolefins Vitrimers: Design Principles and Applications

“…Additionally, when there is a wide distribution in the number of cross-links per chain, phase separation might be amplified. In contrast, the hindered polymeric dynamics of transiently cross-linked entangled polymer chains can compromise phase separation by limiting the accessibility of individual cross-links to each other even above the exchange temperature. , Nevertheless, the frozen network topology of polyolefin vitrimers is prone to contain phase-separated domains, the extent of which is determined by the compromise between thermodynamics and kinetics. Individual cross-links inside phase-separated domains have a higher chance to form misconnectivities such as loops and clusters compared to isolated cross-links in the bulk.…”

“…Stress-relaxation is the most commonly used measurement in vitrimer literature, but it is not suitable for systems whose stress decays by more than three decades. Time–temperature superposition (tTS) is also prone to fail with vitrimers, since generally the temperature dependence of polymeric dynamics and the exchange reactions vary significantly . Therefore, the attainable time or frequency domain cannot be significantly broadened, specifically at longer times or shorter frequencies, respectively, by performing measurements at higher temperatures and applying the tTS law.…”

“…Individual cross-links inside phase-separated domains have a higher chance to form misconnectivities such as loops and clusters compared to isolated cross-links in the bulk. Therefore, despite forming physical junctions with a high connectivity, phase-separated domains contribute less effectively to the network percolation and elasticity compared to the ones that are distributed in the bulk. , Therefore, any incentive that can discourage individual cross-links to phase separate or control the morphology to establish an ordered phase-separated structure can promote not only the mechanical properties but also the recycling efficiency.…”

Metal–ligand complexation and clustering in mussel-inspired side-chain functionalized supramolecular hydrogels

“…Therefore, we hypothesize that at least three relaxation modes are involved in the dynamics of such samples. 31 By including the third relaxation mechanism, the results are generally better compared to those obtained with considering only two relaxation modes. Comparison of the calculated results with the experimental data and the obtained relaxation time spectrum for sample pAA10_NC3 are shown in Fig.…”

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

“…Moreover, leveraging a combination of hydrophobic and electrostatic interactions, the cucurbit uril macrocycle is reported to host different guest molecules with more than 5 orders of magnitude difference in bond stability . Metal–ligand coordination is, however, among the most versatile transient bonds, as it offers the possibility of tuning the bond strength and stability over several orders of magnitude by the mere choice of the metal ion and/or ligand with the least synthesis effort. − The custom design of transient hydrogels is therefore not trivial due to the variety of supramolecular bonds, their unique specificities, besides the choice of the polymer precursor’s nature and topology, and their convoluted supramolecular and macromolecular dynamics . Accordingly, the rational design of a transient hydrogel with favorable viscoelastic behavior is not possible unless by understanding the correlation between their molecular design parameters and macroscopic properties. , …”