Unraveling the Complexity of Supramolecular Copolymerization Dictated by Triazine-Benzene Interactions

Supramolecular Polymer Additives as Repairable Reinforcements for Dynamic Covalent Networks

Employing rigid (in)organic materials as reinforcement for dynamic covalent networks (DCNs) is an effective approach to develop high-performance materials. Yet, recycling of these materials after failure often necessitates inefficient chemical reprocessing or inevitably alters their performance due to unrepairable inert components. Here, a non-covalent reinforcement strategy is presented by introducing a supramolecular additive to a DCN that can reversibly depolymerize and reform on demand, therefore acting as an adaptive and repairable reinforcement. The strong hydrogen-bonding interactions in the supramolecular polymer of triazine-1,3,5-tribenzenecarboxamide (S-T) strengthen the DCN at room temperature, while its non-covalent nature allows for easy one-pot reprocessing at high temperatures. Depending on wether S-T is covalently bond to the DCN or not, it can play either the role of compatibilizer or filler, providing a synthetic tool to control the relaxation dynamics, reprocessability and mechanical properties. Moreover, the S-T reinforcement can be chemically recovered with high yield and purity, showcasing the recyclability of the composite. This conceptually novel supramolecular reinforcement strategy with temperature-controlled dynamics highlights the potential of supramolecular polymer additives to replace conventional unrepairable reinforcements.

Electronically and geometrically complementary perylenediimides for kinetically controlled supramolecular copolymers

The synthesis of 3,4,9,10-benzo[d,e]isoquinolino[1,8-g,h]quinoline-tetracarboxylic diimide (BQQDI) 1 endowed with peripheral trialkoxybenzamide fragments is reported and its self-assembling features investigated. The peripheral benzamide moieties generate metastable monomeric species that afford a kinetically controlled supramolecular polymerization. The electron-withdrawing character of 1 in comparison with previously reported PDIs 2, together with the similar geometry, makes this dye an optimal candidate to perform seeded supramolecular copolymerization yielding four different supramolecular block copolymers. Whilst heteropolymers poly-1-co-2a, poly-2a-co-1 and poly-1-co-2b present an H-type arrangement of the monomeric units, heteropolymer poly-2b-co-1, prepared by seeding the chiral, metastable monomers of 2b with achiral seeds of 1, produces chiral, J-type aggregates. Interestingly, the monosignated CD signal of pristine poly-2b changes to a bisignated CD signal most probably due to the formation of columnar domains around the seeds of 1 which implies the blocky nature of the supramolecular copolymers formed.

Shape-Assisted Self-Assembly of Hexa-Substituted Carpyridines into 1D Supramolecular Polymers

The extent of the influence that molecular curvature plays on the self-assembly of supramolecular polymers remains an open question in the field. We began addressing this fundamental question with the introduction of "carpyridines", which are saddle-shaped monomers that can associate with one another through π-π interactions and in which the rotational and translational movements are restricted. The topography displayed by the monomers led, previously, to the assembly of highly ordered 2D materials even in the absence of strong directional interactions such as hydrogen bonding. Here, we introduce a simple strategy to gain control over the dimensionality of the formed structures yielding classical unidimensional polymers. These have been characterized using well-established protocols allowing us to determine and confirm the self-assembly mechanism of both fibers and sheets. The calculated interaction energies are significantly higher than expected for flexible self-assembling units lacking classical "strong" non-covalent interactions. The versatility of this supramolecular unit to assemble into either supramolecular fibers or 2D sheets with strong association energies highlights remarkably well the potential and importance of molecular shape for the design of supramolecular materials and the applications thereof.

Upcycling Polyolefin Blends into High-Performance Materials by Exploiting Azidotriazine Chemistry Using Reactive Extrusion

The revalorization of incompatible polymer blends is a key obstacle in realizing a circular economy in the plastics industry. Polyolefin waste is particularly challenging because it is difficult to sort into its constituent components. Untreated blends of polyethylene and polypropylene typically exhibit poor mechanical properties that are suitable only for low-value applications. Herein, we disclose a simple azidotriazine-based grafting agent that enables polyolefin blends to be directly upcycled into high-performance materials by using reactive extrusion at industrially relevant processing temperatures. Based on a series of model experiments, the azidotriazine thermally decomposes to form a triplet nitrene species, which subsequently undergoes a complex mixture of grafting, oligomerization, and cross-linking reactions; strikingly, the oligomerization and cross-linking reactions proceed through the formation of nitrogen-nitrogen bonds. When applied to polyolefin blends during reactive extrusion, this combination of reactions leads to the generation of amorphous, phase-separated nanostructures that tend to exist at polymer-polymer interfaces. These nanostructures act as multivalent cross-linkers that reinforce the resulting material, leading to dramatically improved ductility compared with the untreated blends, along with high dimensional stability at high temperatures and excellent mechanical recyclability. We propose that this unique behavior is derived from the thermomechanically activated reversibility of the nitrogen-nitrogen bonds that make up the cross-linking structures. Finally, the scope of this chemistry is demonstrated by applying it to ternary polyolefin blends as well as postconsumer polyolefin feedstocks.

Three-Component Multiblock 1D Supramolecular Copolymers of Ir(III) Complexes with Controllable Sequences

Multicomponent supramolecular block copolymers (BCPs) have attracted much attention due to their potential functionalities, but examples of three-component supramolecular BCPs are rare. Herein, we report the synthesis of three-component multiblock 1D supramolecular copolymers of Ir(III) complexes 1-3 by a sequential seeded supramolecular polymerization approach. Precise control over the kinetically trapped species via the pathway complexity of the monomers is the key to the successful synthesis of BCPs with up to 9 blocks. Furthermore, 5-block BCPs with different sequences could be synthesized by changing the addition order of the kinetic species during a sequentially seeded process. The corresponding heterogeneous nucleation-elongation process has been confirmed by the UV/Vis absorption spectra, and each segment of the multiblock copolymers could be characterized by both TEM and SEM. Interestingly, the energy transfer leads to weakened emission of 1-terminated and enhanced emission of 3-terminated BCPs. This study will be an important step in advancing the synthesis and properties of three-component BCPs.

Fluorescence-readout as a powerful macromolecular characterisation tool

The last few decades have witnessed significant progress in synthetic macromolecular chemistry, which can provide access to diverse macromolecules with varying structural complexities, topology and functionalities, bringing us closer to the aim of controlling soft matter material properties with molecular precision. To reach this goal, the development of advanced analytical techniques, allowing for micro-, molecular level and real-time investigation, is essential. Due to their appealing features, including high sensitivity, large contrast, fast and real-time response, as well as non-invasive characteristics, fluorescence-based techniques have emerged as a powerful tool for macromolecular characterisation to provide detailed information and give new and deep insights beyond those offered by commonly applied analytical methods. Herein, we critically examine how fluorescence phenomena, principles and techniques can be effectively exploited to characterise macromolecules and soft matter materials and to further unravel their constitution, by highlighting representative examples of recent advances across major areas of polymer and materials science, ranging from polymer molecular weight and conversion, architecture, conformation to polymer self-assembly to surfaces, gels and 3D printing. Finally, we discuss the opportunities for fluorescence-readout to further advance the development of macromolecules, leading to the design of polymers and soft matter materials with pre-determined and adaptable properties.

Controllable One-Step Assembly of Uniform Liquid Crystalline Block Copolymer Cylindrical Micelles by a Tailored Nucleation-Growth Process and Their Application as Tougheners

The fabrication of uniform cylindrical nanoobjects from soft materials has attracted tremendous research attention from both fundamental research and practical application points of view but has also posed outstanding challenges in terms of their preparation. Herein, we report a one-step method to assemble cylindrical micelles (CMs) with highly controllable lengths from a single liquid crystalline block copolymer by an in situ nucleation-growth strategy. By adjusting the assembly conditions, the lengths of the CMs are controlled from hundreds of nanometers to micrometers. Several influencing factors are systematically investigated to comprehensively understand the process. Particularly, the solvent quality is found determinative in either enhancing or suppressing the nucleation process to produce shorter and longer CMs, respectively. Taking advantage of this strategy, the lengths of CMs can be nicely controlled over a wide concentration range of four orders of magnitude. Lastly, CMs are produced on decent scales and applied as additives to dramatically toughen glassy plastic matrix, revealing an unprecedented length-dependent toughening effect.

Temperature Directs the Majority-Rules Principle in Supramolecular Copolymers Driven by Triazine-Benzene Interactions

Supramolecular copolymers have typically been studied in the extreme cases, such as self-sorting or highly mixed copolymer systems, while the intermediate systems have been less understood. We have reported the temperature-dependent microstructure in copolymers of triazine- and benzene-derivatives based on charge-transfer interactions with a highly alternating microstructure at low temperatures. Here, we investigate the temperature-dependent copolymerization further and increase the complexity by combining triazine- and benzene-derivatives with opposite preferred helicities. In this case, intercalation of the benzene-derivative into the triazine-derivative assemblies causes a helical inversion. The inversion of the net helicity was rationalized by comparing the mismatch penalties of the individual monomers, which indicated that the benzene-derivative dictates the helical screw-sense of the supramolecular copolymers. Surprisingly, this was not reflected in further investigations of slightly modified triazine- and benzene-derivatives, thus highlighting that the outcome is a subtle balance between structural features, where small differences can be amplified due to the competitive nature of the interactions. Overall, these findings suggest that the temperature-dependent microstructure of triazine- and benzene-based supramolecular copolymers determines the copolymer helicity of the presented system in a similar way as the mixed majority-rules phenomenon.

Supramolecular Block Copolymers from Tricarboxamides. Biasing Co-assembly by the Incorporation of Pyridine Rings

The synthesis of a series of triangular-shaped tricarboxamides endowed with three picoline or nicotine units (compounds 2 and 3, respectively) or just one nicotine unit (compound 4) is reported, and their self-assembling features investigated. The pyridine rings make compounds 2-4 electronically complementary with our previously reported oligo(phenylene ethynylene)tricarboxamides (OPE-TA) 1 to form supramolecular copolymers. C3 -symmetric tricarboxamide 2 forms highly stable intramolecular five-membered pseudocycles that impede its supramolecular polymerization into poly-2 and the co-assembly with 1 to yield copolymer poly-1-co-2. On the other hand, C3 -symmetric tricarboxamide 3 readily forms poly-3 with great stability but unable to form helical supramolecular polymers despite the presence of the peripheral chiral side chains. The copolymer poly-1-co-3 can only be obtained by a previous complete disassembly of the constitutive homopolymers in CHCl3 . Helical poly-1-co-3 arises in a process involving the transfer of the helicity from racemic poly-1 to poly-3, and the amplification of asymmetry from chiral poly-3 to poly-1. Importantly, C2v -symmetric 4, endowed with only one nicotinamide moiety and three chiral side chains, self-assembles into a P-type helical supramolecular polymer (poly-4) in a thermodynamically controlled cooperative process. The combination of poly-1 and poly-4 generates chiral supramolecular copolymer poly-1-co-4, whose blocky microstructure has been investigated by applying the previously reported supramolecular copolymerization model.

Solvent-Induced Pathway Complexity of Supramolecular Polymerization Unveiled Using the Hansen Solubility Parameters

Supramolecular building blocks assembling into helical aggregates are ubiquitous in the current literature, yet the role of solvents in these supramolecular polymerizations often remains elusive. Here, we present a systematic study that quantifies solvent-supramolecular polymer compatibility using the Hansen solubility parameters (δD, δH, and δP). We first studied the solubility space of the supramolecular building block triazine-1,3,5-tribenzenecarboxamide S-T. Due to its amphiphilic nature, a dual-sphere model based on 58 solvents was applied describing the solubility space of the monomeric state (green sphere) and supramolecular polymer state (blue sphere). To our surprise, further in-depth spectroscopic and morphological studies unveiled a distinct solubility region in-between the two spheres giving rise to the formation of higher-order aggregated structures. This phenomenon occurs due to subtle differences in polarity between the solvent and the side chains and highlights the solvent-induced pathway complexity of supramolecular polymerizations. Subsequent variations in concentration and temperature led to the expansion and contraction of both solubility spheres providing two additional features to tune the monomer and supramolecular polymer solubility. Finally, we applied our dual-sphere model on structurally disparate monomers, such as Zn-porphyrin (S-P) and triphenylamine (S-A), demonstrating the generality of the model and the importance of the supramolecular monomer design in connection with the solvent used. This work unravels the solvent-induced pathway complexity of discotic supramolecular building blocks using a parametrized approach in which interactions between the solvent and solute play a crucial role.

Pathway Complexity in Supramolecular Copolymerization and Blocky Star Copolymers by a Hetero-Seeding Effect

This study unravels the intricate kinetic and thermodynamic pathways involved in the supramolecular copolymerization of the two chiral dipolar naphthalene monoimide (NMI) building blocks (O-NMI and S-NMI), differing merely by a single heteroatom (oxygen vs sulfur). O-NMI exhibits distinct supramolecular polymerization features as compared to S-NMI in terms of its pathway complexity, hierarchical organization, and chiroptical properties. Two distinct self-assembly pathways in O-NMI occur due to the interplay between the competing dipolar interactions among the NMI chromophores and amide-amide hydrogen (H)-bonding that engenders distinct nanotapes and helical fibers, from its antiparallel and parallel stacking modes, respectively. In contrast, the propensity of S-NMI to form only a stable spherical assembly is ascribed to its much stronger amide-amide H-bonding, which outperforms other competing interactions. Under the thermodynamic route, an equimolar mixture of the two monomers generates a temporally controlled chiral statistical supramolecular copolymer that autocatalytically evolves from an initially formed metastable spherical heterostructure. In contrast, the sequence-controlled addition of the two monomers leads to the kinetically driven hetero-seeded block copolymerization. The ability to trap O-NMI in a metastable state allows its secondary nucleation from the surface of the thermodynamically stable S-NMI spherical "seed", which leads to the core-multiarmed "star" copolymer with reversibly and temporally controllable length of the growing O-NMI "arms" from the S-NMI "core". Unlike the one-dimensional self-assembly of O-NMI and its random co-assembly with S-NMI, which are both chiral, unprecedentedly, the preferred helical bias of the nucleating O-NMI fibers is completely inhibited by the absence of stereoregularity of the S-NMI "seed" in the "star" topology.

Large Optical Asymmetry in Silver Nanoparticle Assemblies Enabled by CH-π Interaction-Mediated Chirality Transfer

Transfer of asymmetry from the molecular system to the other distinct system requires appropriate chemical interactions. Here, we show how the CH-π interaction, one of the weakest hydrogen bonds, can be applied to transfer the asymmetry from π-conjugated chiral molecules to the assemblies of plasmonic Ag nanoparticles, where the aliphatic chains of chiral molecules and the polystyrene chains grafted on Ag nanoparticles are served as the hydrogen donor and acceptor, respectively. The optical asymmetry g-factor of the chiral assemblies of plasmonic nanoparticles is strongly dependent on the molecular weight of the polystyrene ligand, the core structure of the molecule, and the aliphatic chain length of the chiral molecule. Importantly, we explore a molecular mixing strategy to enhance the asymmetry g-factor of chiral molecular assemblies, which consequently promotes the g-factor of chiral plasmonics efficiently, reaching a high value of ∼0.05 under optimal conditions. Overall, we rationalize the chirality transfer from chiral molecules to inorganic nanoparticles, providing the guidance for structural design of chiral nanocomposites with a high g-factor.

Modular Platform of Carbohydrates-modified Supramolecular Polymers Based on Dendritic Peptide Scaffolds

Glycopeptide supramolecular polymers displaying multivalent carbohydrates are particularly suitable for immune-relevant biomaterials, due to the important functions of carbohydrates in mediating cell-cell communication and modulating immune responses. However, the diversity and complexity of carbohydrates limited the generation of glycopeptide supramolecular monomers. Thereby, a modular platform of presenting various carbohydrates, especially more complex oligosaccharides, is highly desirable but remains underexplored. Here, we first prepared the linear amphiphilic glycopeptides that self-assembled into spherical nanoparticles and worm-like nanoparticles. Furthermore, the dendritic glycopeptides that self-assembled into uniform nanorods were designed to generate modular supramolecular polymers with variable functionality, via redesigning the molecular backbone. With various functional oligosaccharide-modified supramolecular polymers, the in vitro studies further indicated that these polymers were not cytotoxic to macrophages, and significantly modulated the production of proinflammatory cytokines. These findings provide a promising platform to develop supramolecular glycopeptide biomaterials with potential applications in immunomodulation and immunotherapy.

Harmonizing Topological Features of Self-Assembled Fibers by Rosette-Mediated Random Supramolecular Copolymerization and Self-Sorting of Monomers by Photo-Cross-Linking

Random copolymerization is an effective approach to synthesize the desired polymers by harmonizing distinct properties of different monomers. For supramolecular polymers in which monomer binding is inherently dynamic, it is difficult to achieve random copolymerization of monomers with distinct molecular structures and properties due to an enthalpic advantage upon self-recognition (self-sorting). Herein, we demonstrate an example of thermodynamically controlled random supramolecular copolymerization of two monomers functionalized with barbituric acid via the formation of six-membered hydrogen-bonded rosette intermediates to exhibit structural harmonization of the two main-chain motifs, i.e., intrinsically curved and linear motifs. One monomer based on naphthalene chromophore exclusively forms toroidal fibers, whereas another one bearing additional photoreactive diacetylene moiety affords linearly elongated fibers. Supramolecular copolymerization of the two monomers is achieved by cooling hot monomer mixtures in a nonpolar solvent, which results in the formation of thermodynamically stable spirally folded yet elongated fibers. Atomic force microscopic observations and theoretical simulations of the experimental data obtained by absorption spectroscopy reveal the homopolymerization of the diacetylene-functionalized monomer in the high-temperature region, followed by the incorporation of the naphthalene monomer in the medium-temperature region to form supramolecular copolymers with random monomer sequence. Finally, we demonstrate that the random copolymerization process can be switched to a narcissistically self-sorting one by deactivating monomer exchange through the photo-cross-linking of the diacetylene-functionalized monomers.

A Strategy Based on Aggregation-Induced Ratiometric Emission to Differentiate Molecular Weight of Supramolecular Polymers

Molecular weight has an important bearing on the properties of supramolecular polymers. However, the intuitive differentiation of the molecular weight of supramolecular polymers remains challenging. Given this situation, establishing a reliable relationship between fluorescence properties and molecular weight may be a promising strategy. Herein, we prepared a supramolecular monomer M1 with aggregation-induced ratiometric emission characteristics. With the increasing M1 concentration (0.100-100 mM), the average degree of polymerization (DP_DOSY ) rose from 1.00 to 293. Meanwhile, the color changed from dark blue to cyan, finally to yellow-green in the same concentration range. Hence, the intuitive relationship between DP_DOSY and fluorescence colors was constructed, allowing the visual differentiation of molecular weight. Moreover, the fluorescence color could be regulated by introducing a competitive molecule to induce the depolymerization of supramolecular polymers.

Chirality-Controlled Supramolecular Donor-Acceptor Copolymerization with Distinct Energy Transfer Efficiency

Chirality delivers substantial value to the field of supramolecular polymers, not only serving as a probe to monitor the dynamic assembly process but providing access to chiroptical materials. The current study demonstrates that, for supramolecular donor-acceptor copolymers, their comonomer organization modes can be greatly influenced by stereocommunication at the molecular level. The enantiopure N-[(1R or 1S)-phenylethyl]benzamides are incorporated into two structurally similar comonomers, locating between the π-aromatic diethynylacene core and the alkyl chain peripheries. Parallel arrangement of the stereogenic methyl units brings steric hindrance between the homochiral comonomers, which is relieved for the heterochiral comonomers due to the adoption of staggered arrangement. It consequently steers randomly mixed organization for the homochiral supramolecular copolymers within the nanofibers. In comparison, the heterochiral counterparts form nanoparticles in an alternate donor-acceptor organization manner. The variation of comonomer arrangement modes gives rise to distinct energy transfer efficiency at the supramolecular level. Overall, the elaborate manipulation of stereogenic centers in the comonomer structures exerts significant impacts on the characteristics of supramolecular copolymers, which could be useful for chiral sensing, recognition, and optoelectronic applications.

Self-sorting assembly of artificial building blocks

Self-assembly to build high-level structures, which is ubiquitous in living systems, has captured the imagination of scientists, striving to emulate the intricacy, homogeneity and versatility of the naturally occurring systems, and to pursue a similar level of organization in artificial building blocks. In particular, self-sorting assembly in multicomponent systems, based on the spontaneous recognition and consequent spatial aggregation of the same or interactive building units, is able to realize very complicated assembly behaviours, and usually results in multiple well-ordered products or hierarchical structures in a one-step manner. This highly efficient assembly strategy has attracted tremendous research attention in recent years, and numerous examples have been reported in artificial systems, particularly with supramolecular and polymeric building blocks. In the current review, we summarize the progress in recent years, and classify them into five main categories, based on their working mechanisms or principles. With the review of these strategies, we hope to provide not only some deep insights into this field, but also and more importantly, useful thoughts in the design and fabrication of self-sorting systems in the future.