The properties and function of supramolecular polymer networks are determined not only by pairwise interchain transient associations but also by chain entanglement and nanoscopic phase separation of the associative groups. To unravel the impact and interplay of these different factors, we devise a set of model supramolecular polymer networks in which the number of entanglements and the density of associative groups are systematically varied. Rheological data show that by increasing the density of associative groups, the plateau modulus grows to a steady level and extends over a distinct frequency range. This is credited to the presence of binary associations with unique partner exchange time. For samples where the high-frequency plateau stays at the constant level, a second plateau emerges at low frequencies in addition. This plateau, which is well below the entanglement plateau of the precursor, is attributed to the presence of collective assemblies of nanophase-separated associative groups, as confirmed by FTIR spectroscopy. The contributions of these two different levels of interchain associations are decoupled on the basis of a tube-based model. The obtained model parameters show that by increasing the number of network junctions, including both interchain associations and entanglements, the fraction of binary associations decreases, while the density of collective ones approaches a constant level.

In this review, the origin of clusters in supramolecular polymer materials, their characterization, their effects on the dynamic and mechanical properties, and their potentials for designing functional materials are overviewed.

The dynamic mechanical properties of supramolecular associative polymer networks depend on the average number of entanglements along the network-forming chains, N e , and on their content of associative groups, f. In addition, there may be further influence by aggregation of the associative groups into clusters, which, in turn, is influenced by the chemical structure of these groups, and again by N e and f of the polymer. Therefore, the effects of these parameters are interdependent. To conceptually understand this interdependency, we study model networks in which (a) N e , (b) f, and (c) the chemical structure of the associative groups are varied systematically. Each network is probed by rheology. The clustering of the associative groups is assessed by analyzing the rheological data at the end range of frequency covered and by comparison of the number of supramolecular network junctions with the maximum possible number of binary transient bonds. We find that if the total number of the network junctions, which can be formed either by interchain entanglement or by interchain transient associations, is greater than a threshold of 13, then the likelihood of cluster formation is high and the dynamics of supramolecular associative polymer networks is mainly controlled by this phenomenon.

Defect engineering is a success story in crystalline hard matter; this review summarizes its parallels in amorphous soft matter.

The chain dynamics in supramolecular polymer networks is determined by the interplay of the kinetics of transient interchain association and relaxation of the network chains themselves. This interplay can be addressed by studying model supramolecular polymer networks in which the number of associative side groups and the molar mass of the covalently jointed backbone polymers are both varied systematically. To realize this idea, we use precursor chains with three different molar masses, which comes along with different extents of entanglement in the melt state. For each molar mass, the precursor polymers are functionalized with three different relative contents of associative side groups, giving rise to transient network formation in the melt state. We evaluate the chain dynamics in these transient networks by probing the diffusivity of fluorescently labeled tracer chains by fluorescence recovery after photobleaching (FRAP). In these studies, we find that the presence of entanglements markedly outweighs the influence of transient associative interactions.

Dynamics of entangled polymer chains in the melt state are deliberately excluded in most of the studies on supramolecular polymer networks by utilizing nonentangled precursor chains. Relaxation of the system mainly depends on the dissociation of the associative groups in latter case and nonentangled chains deliver nothing to resist afterward. Conversely, in an entangled system, relaxation of polymer chains and dissociation of associative groups can occurred parallel.Supramolecular networks based on an entangled precursor polymer with different levels of strong associating ureidopyrimidinone (UPy) groups are synthesized to screen the corresponding effects on the dynamics of the system. Binary-associated UPy groups phase separate into collective assemblies by stacking and form high-order, needle-like domains at higher UPy contents. Relaxation of polymer chains is significantly hindered due to the trapping of polymer segments between UPy stacks. Above a certain threshold of UPy content (~4 mol%), the plateau level and final relaxation time of networks show a significant jump, which is attributed to the onset of high-order association of UPy groups. KEYWORDS chain dynamics, high-order associations, supramolecular networks 1 | INTRODUCTION Supramolecular polymer networks are macromolecular structures in which a fraction of covalent bonds are replaced with transient associations, 1-6 such as ionic attractions, 7-11 metal-ligand coordinations, [12][13][14][15][16][17] hydrogen bondings, 18-21 or π-π interactions. 22,23 Such transient bonds are in the dynamic equilibrium between associated and dissociated states. Consequently, supramolecular polymer networks response to the external stimuli and have potential to use for designing electronic, 24,25 optic-electronic, 26,27 drug-delivery, 28-32 and/or selfhealing 17,33-40 materials. The supramolecular polymer networks are divided in 2 general types. In the first type, the polymeric building blocks have associative groups at both extremities, and the virtual molar mass is increased by chain extension due to the self-assembly of end groups.In the second type, the linear or branched polymer chains carry pendant associative "sticky" groups. 41 Hydrogen bonding moieties are widely used for designing supramolecular polymers, since they demonstrate very broad range of strength, which can be controlled by the number and the configuration of the interactions. 42,43 One of these promising moieties is ureidopyrimidinone (UPy) group, which self-assembles with highstrength, quadruple hydrogen bonds. [44][45][46][47][48][49][50] Low molar mass telechelic polymers that are viscous liquid at room temperature show properties like solid polymers after functionalization with UPy groups. [51][52][53][54][55][56][57] Binary-associated UPy moieties create π-π stacking when the UPy motifs are linked to the building block chains by urethane or urea groups, which can form lateral-secondary interactions. 56,[58][59][60] The formation of micrometer long fibers in the morphology of UPy-functionalized...

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.

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