Supramolecular Block Copolymers Research Articles

Supramolecular copolymerization of hydrophobic and hydrophilic monomers in liquid crystalline media.

In the case of covalent polymers, immiscible polymers can be integrated by covalently linking them together, but such a strategy is not possible in supramolecular polymers. Here we report the supramolecular copolymerization of two porphyrin-based monomers, C10P2H and TEGPCu with side chains bearing cyanobiphenyl (CB) groups at the ends of hydrophobic alkyl or hydrophilic tetraethylene glycol chains, respectively. These monomers undergo self-sorting supramolecular polymerization in highly diluted solutions ([monomer] = 3.4 × 10-9 mol% (2.0 × 10-8 mol L-1)) in nonpolar media due to the incompatibility of the side chains. Surprisingly, these monomers undergo supramolecular copolymerization under high concentration conditions ([monomer] = 7.7 mol%) in the medium of 4-cyano-4'-pentyloxybiphenyl (5OCB) to form a columnar liquid crystalline phase under thermodynamic conditions, where the individual columns are composed of supramolecular block copolymers. The combination of CB ends of both monomers and the 5OCB medium is essential for the two monomers to form an integrated structure in a condensed system without phase separation.

Strategies for Synthesizing Supramolecular Block Copolymers.

Over the past decade, controlled supramolecular polymerization has been extensively studied and gradually shifted to supramolecular block copolymerization. Supramolecular block copolymers (BCPs) are considered the holy grail for developing supramolecular materials with new functionalities due to their fascinating structures and ability to introduce diverse functions. From a thermodynamic view to kinetic aspects, great progress has been made in the synthetic strategies of BCPs in the past few years. This Concept summarizes various strategies to realize supramolecular block copolymerization. The focus is on providing researchers with a methodological basis for achieving heterogeneous nucleation-elongation.

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.

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

AbstractMulticomponent 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.

Visible Light-Guided Gene Delivery with Nonviral Supramolecular Block Copolymer Vectors.

To achieve efficient gene delivery in vitro or in vivo, nonviral vectors should have excellent biostability across cellular and tissue barriers and also smart stimuli responsiveness toward controlled release of therapeutic genes into the cell nucleus. However, it remains a key challenge to effectively combine the biostability of covalent polymers with the stimuli responsiveness of noncovalent polymers into one nonviral vehicle. In this work, we report the construction of a kind of cationic supramolecular block copolymers (SBCs) through noncovalent polymerization of β-cyclodextrin/azobenzene-terminated pentaethylenehexamine (DMA-Azo-PEHA-β-CD) in aqueous media using β-CD-monosubstituted poly(ethylene glycol) (PEG-β-CD) as a supramolecular initiator. The resultant SBC exhibits superior biostability, biocompatibility, and light/pH dual-responsive characteristics, and it also demonstrates efficient plasmid DNA condensation capacity and the ability to rapidly release plasmid DNA into cells driven by visible light (450 nm). Eventually, this SBC-based delivery system demonstrates visible light-induced enhancement of gene delivery in both COS-7 and HeLa cells. We anticipate that this work provides a facile and robust strategy to enhance gene delivery in vitro or in vivo via visible light-guided manipulation of genes, further achieving safe, highly efficient, targeting gene therapy for cancer.

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

The synthesis of a series of triangular-shape tricarboxamides endowed with three picolin or nicotin (compounds2and3) or just one nicotine unit (compound4) is reported and their self-assembling features investigated. The pyridine rings make compounds2-4electronically complementary with our previously reported OPETA1to form supramolecular copolymers.C3-symmetric tricarboxamide2forms highly stable intramolecular five-membered pseudocycles that impedes its supramolecular polymerization intopoly-2and the co-assembly with1to yield copolymerpoly-1-co-2. On the other hand,C3-symmetric tricarboxamide3readily formpoly-3with great stability but unable to form helical supramolecular polymers despite the presence of the peripheral chiral side chains. The copolymerpoly-1-co-3can only be obtained by a previous complete disassembly of the constitutive homopolymers in CHCl3. Helicalpoly-1-co-3arises in a process involving the transfer of the helicity from racemicpoly-1topoly-3, and the amplification of asymmetry from chiralpoly-3topoly-1. Importantly,C2v-symmetric4, endowed with only one nicotinamide moiety and three chiral side chains, self-assembles intoP-type helical supramolecular polymer (poly-4) in a thermodynamically controlled cooperative process. The combination ofpoly-1andpoly-4generates chiral supramolecular copolymerpoly-1-co-4, whose blocky microstructure has been investigated by applying the supramolecular copolymerization model.

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

AbstractThe 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.

Controlling the Supramolecular Polymerization of Squaraine Dyes by a Molecular Chaperone Analogue

Molecular chaperones are proteins that assist in the (un)folding and (dis)assembly of other macromolecular structures toward their biologically functional state in a non-covalent manner. Transferring this concept from nature to artificial self-assembly processes, here, we show a new strategy to control supramolecular polymerization via a chaperone-like two-component system. A new kinetic trapping method was developed that enables efficient retardation of the spontaneous self-assembly of a squaraine dye monomer. The suppression of supramolecular polymerization could be regulated with a cofactor, which precisely initiates self-assembly. The presented system was investigated and characterized by ultraviolet-visible, Fourier transform infrared, and nuclear magnetic resonance spectroscopy, atomic force microscopy, isothermal titration calorimetry, and single-crystal X-ray diffraction. With these results, living supramolecular polymerization and block copolymer fabrication could be realized, demonstrating a new possibility for effective control over supramolecular polymerization processes.

Mechanically tunable supramolecular polymer networks with different triblock backbones

AbstractSupramolecular polymer networks (SPNs) have attracted much research attention due to their good performance in the preparation of adaptive materials. Controlling the distribution of supramolecular interactions in the networks is a good strategy to tune the properties of SPNs, but corresponding study is still rare. Herein, we construct two triblock copolymers in ABA and BAB forms to control the supramolecular interaction concentrated in A block, leading to two SPNs with divergent mechanical performances. In specific, the SPN‐1 formed by ABA triblock copolymer displays a slightly and densely distributed hard domain and a compact network, resulting in a decent toughness. While the SPN‐2 composed of BAB triblock copolymer is rigid and less elastic, whose microphase‐separated structures are more obvious, making the network difficult to withstand larger strains. These findings are conducive to deepening the understanding of SPNs and would promote the development of supramolecular block copolymers with emergent functions and applications.

Automated Supramolecular Polymerization in a Microflow: A Versatile Platform for Multistep Supramolecular Reactions.

This work reports a basic microflow system capable of performing multistep supramolecular polymerization. In this system, injection of the monomer, directional supramolecular copolymerization, removal of the unreacted monomer, and purification of the product supramolecular diblock copolymers are realized along a three-stream flow. When injecting a supramolecular polymer into the central stream of the three-stream flow, the supramolecular polymerization always occurs in the central flow, with the two lateral flows serving as supply and removal lines for the monomer. Employing two kinds of perylene bisimide derivatives as monomers, we confirmed that the reaction occurred selectively at the forward-facing terminus of the supramolecular polymer, along with recovery of the unreacted monomer, ultimately leading to a high-purity supramolecular diblock copolymer. Diblock copolymers are basic units for preparing multicomponent supramolecular block copolymers. Thus, connecting the present system in series would, in principle, result in a "microplant" capable of producing supramolecular polymers having desired inner complexity.

Synthesis and self-assembly of fluorinated supramolecular mesogen-jacketed liquid crystalline polymer and its high-χ block copolymer constructed by hydrogen bonding

By connecting a fluorinated molecule 2,5-bis((4-(perfluorohexyl)benzoyl)oxy)benzoic acid (6DFP) to the poly(4-vinylpyridine) (P4VP) backbone through hydrogen bonding, we synthesized a new series of fluorinated supramolecular mesogen-jacketed liquid crystalline polymer (MJLCP) P4VP(6DFP)x, where x is the molar ratio of donor to acceptor. Polarized light microscopy and wide-angle X-ray scattering were used to investigate the liquid crystallinity of the resulting complexes. The results show that this kind of supramolecular MJLCP has good thermal stability, with the isotropization temperature of about 170 °C. Subsequently, by connecting the fluorinated molecule 6DFP to the commercially available coil−coil block copolymer (BCP) polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) chain also via hydrogen bond, we constructed a series of supramolecular rod−coil BCP PSmVn(6DFP)x, where m and n are the degrees of polymerization of PS and P4VP, respectively. PSmVn(6DFP)x exhibits a hierarchically ordered self-assembled structure. Owing to the introduction of fluorine atoms, the Flory-Huggins interaction parameter (χ) of such a supramolecular BCP is high. BCP sample with a low total degree of polymerization can still be ordered, and the periodic size can be as low as 11.5 nm. This work provides a new approach for the construction of small-sized structures by supramolecular BCPs via hydrogen bonding, which can be used as nanotemplates and nanoporous materials after selective removal of the small molecules.

Asymmetric Living Supramolecular Polymerization: Precise Fabrication of One-Handed Helical Supramolecular Polymers.

Programming the organization of semiconducting polymers to form well-defined nanoarchitectures is desirable for fabricating functional materials. In this work, semiconducting copolymers, poly(cholesterol allene)-b-poly(3-hexylthiophene) (PCA-b-P3HT) containing helical PCA and poly(alkoxy allene)-b-poly(3-hexylthiophene) (PAA-b-P3HT) containing achiral PAA segments, were prepared. Crystallization of P3HT and helicity of PCA drove PCA-b-P3HT self-assemble into spherical nanoparticles that gradually transformed into one-handed helical nanofibers. The chirality of PCA was transferred to the supramolecular architectures, induced high optical activity in P3HT. Interestingly, the chiral seed micelles of PCA-b-P3HT induced asymmetric copolymerization of achiral PAA-b-P3HT, which led to helical supramolecular block copolymers with defined helicity and controlled length. Remarkably, the supramolecular copolymers showed white-light emission and circularly polarized luminescence.

Asymmetric Living Supramolecular Polymerization: Precise Fabrication of One‐Handed Helical Supramolecular Polymers

AbstractProgramming the organization of semiconducting polymers to form well‐defined nanoarchitectures is desirable for fabricating functional materials. In this work, semiconducting copolymers, poly(cholesterol allene)‐b‐poly(3‐hexylthiophene) (PCA‐b‐P3HT) containing helical PCA and poly(alkoxy allene)‐b‐poly(3‐hexylthiophene) (PAA‐b‐P3HT) containing achiral PAA segments, were prepared. Crystallization of P3HT and helicity of PCA drove PCA‐b‐P3HT self‐assemble into spherical nanoparticles that gradually transformed into one‐handed helical nanofibers. The chirality of PCA was transferred to the supramolecular architectures, induced high optical activity in P3HT. Interestingly, the chiral seed micelles of PCA‐b‐P3HT induced asymmetric copolymerization of achiral PAA‐b‐P3HT, which led to helical supramolecular block copolymers with defined helicity and controlled length. Remarkably, the supramolecular copolymers showed white‐light emission and circularly polarized luminescence.

Self-assembly of gold nanoparticles grafted with amphiphilic supramolecular block copolymers

Design of polymer grafted plasmonic metal nanoparticles (PGNPs) has received continuous interest due to polymer-driven self-assembly of plasmonic nanoparticles (NPs) as a means to control interparticle plasmon coupling in ensembles. We report the use of supramolecular “V-shaped” block copolymers (VBCPs) as surface ligands of PGNPs to study their hydrophobicity-driven self-assembly. The amphiphilic VBCPs are prepared from two homopolymers, namely dipicolyamine (DPA)-terminated polystyrene (PS) and pyridine (Py)-terminated poly(N,N-dimethylacrylamide) (PDMA) where the two polymers are bridged with Cu2+ ions. Those supramolecular VBCPs formed spherical micelles in the range of 100–300 nm, much larger than those of linear BCPs with similar chemical composition as a result of Cu2+ ions at the hydrophobic/hydrophilic interface. Thioester-containing supramolecular polymers can modify plasmonic AuNPs through ligand exchange even in the presence of Cu2+ ions. Those supramolecular polymers can drive PGNPs to form giant vesicles and two-dimensional (2-D) layered nanosheets. Using in situ light scattering, the supramolecular dynamics is found to allow maximum chain reconformation of polymer ligands where the interparticle distance of PGNPs grafted with VBCPs is smaller compared to that of PGNPs with linear BCPs. The assembled nanostructures with VBCPs also showed similar stimuli-responsive properties where the dissociation of DPA-Cu2+-Py coordination results in the disruption of assembled nanostructures. The supramolecular approaches potentially provide a new toolbox to design PGNP assemblies with tunable nanostructures and interesting dynamic properties enabled by non-covalent interaction.

A simple route to prepare supramolecular block copolymers using telechelic polystyrene/polydimethylsiloxane pairs

AbstractWhile supramolecular block copolymer (BCP) self‐assembly has been widely studied over the past decades as an effective means to generate functional nanomaterials, most of these systems require multiple steps of synthesis and processing. In this report, we introduce a facile approach to form linear multiblock copolymers by directly blending telechelic homopolymer pairs, using di‐sulfonated polystyrene and commercially available, aminopropyl terminated polydimethylsiloxane. A series of model multiblock copolymers were prepared, in which proton transfers between polymer chain ends enable the formation of strong ionic associations. These ionic junctions not only significantly enhance thin film stability of polymer blends by forming higher molecular weight copolymers, but also improve the chemical incompatibility between different segments, resulting in ordered nanostructures upon self‐assembly. These include different morphologies such as lamellae and cylinders. We also demonstrate that feature size of these BCPs can be adjusted by varying the molecular weight of the homopolymers, with a smallest domain spacing of approximately 12.9 nm being obtained. Utilizing low‐cost and widely available polymers as building blocks, our simple and efficient supramolecular assembly strategy for forming multiblock copolymers may provide a promising platform for cost‐efficient nanomanufacturing of polymeric materials. © 2021 Society of Industrial Chemistry.

Photonic Particles Made by the Confined Self-Assembly of a Supramolecular Comb-Like Block Copolymer.

Approaches that enable the preparation of robust polymeric photonic particles are of interest for the development of nonfading and highly reflective pigments for applications such as paints and display technologies. Here, the preparation of photonic particles that display structural color in both, aqueous suspension and the dry solid state is reported. This is achieved by exploiting the confined self-assembly of a supramolecular comb-like block copolymer (BCP) that microphase separates into a well-ordered lamellar morphology with dimensions that promote a photonic bandgap in the visible range. The comb-like BCP is formed by robust ionic interactions between poly(styrene-b-4-vinyl-pyridine) (PS-b-P4VP) BCP and dodecylbenzene sulfonic acid (DBSA), which selectively interacts with P4VP blocks. The components are combined in chloroform, and an aqueous emulsion is prepared. Evaporation of the organic solvent leads to the formation of solid microparticles with an onion-like 3D morphology. These photonic pigments display brilliant colors with reflectance spectra featuring pronounced optical bandgaps across the entire visible wavelength range with a peak reflectivity of 80-90%.

Tricomponent Supramolecular Multiblock Copolymers with Tunable Composition via Sequential Seeded Growth.

Synthesis of supramolecular block co-polymers (BCP) with small monomers and predictive sequence requires elegant molecular design and synthetic strategies. Herein we report the unparalleled synthesis of tri-component supramolecular BCPs with tunable microstructure by a kinetically controlled sequential seeded supramolecular polymerization of fluorescent π-conjugated monomers. Core-substituted naphthalene diimide (cNDI) derivatives with different core substitutions and appended with β-sheet forming peptide side chains provide perfect monomer design with spectral complementarity, pathway complexity and minimal structural mismatch to synthesize and characterize the multi-component BCPs. The distinct fluorescent nature of various cNDI monomers aids the spectroscopic probing of the seeded growth process and the microscopic visualization of resultant supramolecular BCPs using Structured Illumination Microscopy (SIM). Kinetically controlled sequential seeded supramolecular polymerization presented here is reminiscent of the multi-step synthesis of covalent BCPs via living chain polymerization. These findings provide a promising platform for constructing unique functional organic heterostructures for various optoelectronic and catalytic applications.

Living supramolecular polymerization of fluorinated cyclohexanes

The development of powerful methods for living covalent polymerization has been a key driver of progress in organic materials science. While there have been remarkable reports on living supramolecular polymerization recently, the scope of monomers is still narrow and a simple solution to the problem is elusive. Here we report a minimalistic molecular platform for living supramolecular polymerization that is based on the unique structure of all-cis 1,2,3,4,5,6-hexafluorocyclohexane, the most polar aliphatic compound reported to date. We use this large dipole moment (6.2 Debye) not only to thermodynamically drive the self-assembly of supramolecular polymers, but also to generate kinetically trapped monomeric states. Upon addition of well-defined seeds, we observed that the dormant monomers engage in a kinetically controlled supramolecular polymerization. The obtained nanofibers have an unusual double helical structure and their length can be controlled by the ratio between seeds and monomers. The successful preparation of supramolecular block copolymers demonstrates the versatility of the approach.

Healable soft materials based on ionic liquids and block copolymer self-assembly

Ion gels, which are macromolecular networks filled with ionic liquids, are attracting significant interest owing to their unique physicochemical properties such as their nonflammability, negligibly low volatility, and high ionic conductivity. However, for greater applicability in electrochemical devices, these materials must have high mechanical strength while continuing to exhibit the desirable properties of ionic liquids. Therefore, functional ion gels that can self-heal in response to external stimuli or in an autonomous fashion are being investigated. In this review, we highlight the recent progress made by our group in the development of healable ion gels formed by the self-assembly of block copolymers in ionic liquids. First, photohealable ion gels that exploit the photoinduced morphological transitions of block copolymers in ionic liquids are described. Then, the molecular design of self-healing block copolymer-ion gels that show fast self-healing as well as high mechanical strength is discussed. Our recent development on healable soft materials that utilize block copolymer self-assembly in ionic liquids is reviewed. We begin by discussing photohealable ion gels that respond to specific wavelength of light irradiation by forming and collapsing stimuli-responsive networks. Then, we highlight on the self-healing ion gels based on synergetic combination of supramolecular interaction and block copolymer self-assembly, which realize high mechanical strength and fast self-healing ability in the absence of any external stimuli.

Supramolecular Functionalizable Linear-Dendritic Block Copolymers for the Preparation of Nanocarriers by Microfluidics.

Hybrid linear–dendritic block copolymers (LDBCs) having dendrons with a precise number of peripheral groups that are able to supramolecular bind functional moieties are challenging materials as versatile polymeric platforms for the preparation of functional polymeric nanocarriers. PEG2k-b-dxDAP LDBCs that are based on polyethylene glycol (PEG) as hydrophilic blocks and dendrons derived from bis-MPA having 2,6-diacylaminopyridine (DAP) units have been efficiently synthesized by the click coupling of preformed blocks, as was demonstrated by spectroscopic techniques and mass spectrometry. Self-assembly ability was first checked by nanoprecipitation. A reproducible and fast synthesis of aggregates was accomplished by microfluidics optimizing the total flow rate and phase ratio to achieve spherical micelles and/or vesicles depending on dendron generation and experimental parameters. The morphology and size of the self-assemblies were studied by TEM, Cryogenic Transmission Electron Microscopy (cryo-TEM), and Dynamic Light Scattering (DLS). The cytotoxicity of aggregates synthesized by microfluidics and the influence on apoptosis and cell cycle evaluation was studied on four cell lines. The self-assemblies are not cytotoxic at doses below 0.4 mg mL−1. Supramolecular functionalization using thymine derivatives was explored for reversibly cross-linking the hydrophobic blocks. The results open new possibilities for their use as drug nanocarriers with a dynamic cross-linking to improve nanocarrier stability but without hindering disassembly to release molecular cargoes.