Supramolecular Polymer Networks Research Articles

Cytosine-Functionalized Supramolecular Polymer-Mediated Cellular Behavior and Wound Healing

Physically cross-linked supramolecular polymers composed of a hydrophobic poly(epichlorohydrin) backbone with hydrogen-bonding cytosine pendant groups and hydrophilic poly(ethylene glycol) (PEG) side chains spontaneously self-assemble to form highly controlled, reversible supramolecular polymer networks (SPNs) because of cytosine-induced transient cross-linking. Owing to their simple synthesis procedure and ease of tuning the cytosine and PEG contents to obtain varying degrees of SPNs within the polymer matrix, the resulting polymers exhibit a unique surface morphology, wide-range tunable mechanical/rheological properties, and surface wettability behavior as well as high biocompatibility and structural stability in normal cell- and red blood cell-rich media. Cell culture experiments and fluorescent images clearly demonstrated that the incorporation of cytosine and PEG units into the SPN-based polymer substrates efficiently promoted cellular attachment and accelerated cell growth. Importantly, scratch wound-healing assays revealed that the cytosine-functionalized substrates promoted rapid cell spreading and migration into the damaged cellular surface and accelerated the wound-healing rate. These results indicate that the presence of cytosine units within polymer substrates is crucial for the construction of multifunctional tissue engineering scaffolds with tailorable physical characteristics in order to promote cell adhesion, proliferation, and differentiation.

Tuning the Self-Healing Response of Poly(dimethylsiloxane)-Based Elastomers

We present a comprehensive investigation of mechanical properties of supramolecular polymer networks with rationally developed multistrength hydrogen-bonding interactions. Self-healing poly(dimethy...

Functional Supramolecular Polymeric Networks: The Marriage of Covalent Polymers and Macrocycle-Based Host-Guest Interactions.

Covalent polymers connected by non-covalent interactions constitute a fascinating set of materials known as supramolecular polymer networks (SPNs). A key feature of SPNs is that the underlying covalent polymers endow the resulting self-assembled materials with features, such as structural and mechanical integrity, good processability, recyclability, stimuli-responsiveness, self-healing, and shape memory, that are not recapitulated in the case of classic covalent polymer systems. The unique nature of SPNs derives from the controlled marriage of traditional covalent polymers and macrocycle-based host-guest interactions. As a consequence, supramolecular polymeric networks have played important roles in a number of diverse fields, including polymer science, supramolecular chemistry, materials science, biomedical materials, and information storage technology. In this Review, we summarize advances made in the area of functional SPNs, with a focus on original literature reports appearing in the past five years. The treatment is organized according to the key macrocycle-based host-guest interactions used to produce various SPNs. The role of the underlying polymer backbones is also discussed.

A pillar[5]arene-based supramolecular polymer network gel and its application in adsorption and removal of organic dye in water

A novel 3D supramolecular polymer network gel (DP5G) was successfully constructed by easy to synthesize tripodal guest (SZ) and thioacetylhydrazone functionalized di-pillar[5]arene host (DP5). Interestingly, the DP5G showed aggregation induced emission (AIE). Moreover, the DP5G displayed a 3D network structure, which was used to dye removal experiments. Notably, the xerogel DP5G could effectively remove cationic dyes (including crystal violet and rhodamine B) from aqueous solution and the removal percentages are 96.3% and 95.4%, respectively. In addition, the maximal adsorption capacity of DP5G towards crystal violet and rhodamine B are 19.65 mg/g and 22.85 mg/g, respectively. The stability of the 3D supramolecular polymer network gel (DP5G) was further investigated, which exhibited excellent stability toward outer stimuli such as pH, competitive agents, oxidant and reducing agent.

Nonlinear rheology and dynamics of supramolecular polymer networks formed by associative telechelic chains under shear and extensional flows

Nonequilibrium computer simulations have been applied to study the shear and extensional flow behavior of supramolecular polymer networks (SPNs) formed by unentangled and weakly entangled associative telechelic chains and their nonassociative polymer melt counterparts. The reversible bonding of the associative end monomers or stickers leads to the formation of percolated transient networks and consequently stronger mechanical properties of the SPNs than their melt counterparts. In startup shear, the transient shear viscosities η ( t ) and first normal stress coefficients Ψ 1 ( t ) of both the SPN and melt systems show overshoot behavior, but only the SPNs demonstrate transient strain hardening at high shear rates. In startup planar extensional flows, all systems demonstrate the characteristic extensional strain hardening behavior. The transient extensional viscosities η E ( t ) of the SPNs undergo a small overshoot before entering the steady state, which was not observed in the nonassociative polymer melts. For both types of polymer systems with unentangled and weakly entangled chain lengths, the steady-state shear viscosities show typical shear-thinning behavior, while the steady-state extensional viscosities demonstrate extension hardening, which are consistent with published simulation and experimental works. The observed flow behavior can be well understood from the flow-induced non-Gaussian chain stretching and segment orientation in all polymer systems studied, as well as the additional relaxation mechanisms in the SPNs, including the flow-induced reduction in the density of elastically active strands, the increment in the probability for the stickers to exchange their associated partners, and the reduction in the average sticky bond lifetimes at high strain rates.

A Self-Cross-Linking Supramolecular Polymer Network Enabled by Crown-Ether-Based Molecular Recognition.

Supramolecular polymers based on host-guest molecular recognition have emerged as promising platforms for the development of smart materials. However, the studies on them are primarily conducted in solution and/or in the gel state. In contrast, little is known about dynamic properties and applications of supramolecular polymers in bulk. Herein, we present a self-cross-linking supramolecular polymer network (SPN) as a model system to understand the bulk properties controlled by noncovalent interactions. Specifically, the SPN monomer is composed of two benzo-21-crown-7 (B21C7) host units and two dialkylammonium salt guest moieties on a four-arm core, wherein complementary host-guest complexation drives the formation of the SPN with [2]pseudorotaxane linkages between B21C7 and ammonium motifs. The dynamic and reversible behaviors of the linkages are evaluated by measurement of viscoelasticity. The results indicate that the host-guest molecular recognition becomes highly dynamic at elevated temperature. Moreover, the relatively high activation energy of the SPN manifests itself as a new type of thermoplastic material with network topology freezing glass transition. Finally, we demonstrate how these findings provide insights into the malleability and processability of the SPN by simple demos. The fundamental understanding gained from the research on this SPN in bulk will facilitate the advancement and application of supramolecular materials.

Stimuli-responsive supramolecular polymer network based on bi-pillar[5]arene for efficient adsorption of multiple organic dye contaminants

A novel supramolecular polymer network gel has been successfully prepared via bi-pillar[5]arene and a tripodal guest, exhibiting multi-stimuli-responsiveness and efficient adsorption of organic dyes.

Supramolecular polymer networks based on pillar[5]arene: synthesis, characterization and application in the Fenton reaction.

A new type of supramolecular polymeric material was constructed efficiently via orthogonal pillar[5]arene-based host-guest and hydrogen bond interactions. The supramolecular polymeric materials prove to be a good catalyst for the Fenton reaction in water.

Facile construction of a double network cross-linked luminescent supramolecular elastomer by hydrosilylation and pillar[5]arene host-guest recognition.

Reticulated copolymer host pillar[5]arene cross-linked with poly(dimethylsiloxane) (PDMS) was synthesized for the facile construction of a double network cross-linked elastomer upon noncovalently cross-linking with tetraphenyethylene (TPE)-based tetratopic guests through host-guest interactions. The obtained sample strips had better mechanical properties and luminescence capabilities.

Addition to “Dominance of Chain Entanglement over Transient Sticking on Chain Dynamics in Hydrogen-Bonded Supramolecular Polymer Networks in the Melt”

Addition to “Dominance of Chain Entanglement over Transient Sticking on Chain Dynamics in Hydrogen-Bonded Supramolecular Polymer Networks in the Melt”

3D Printing of Supramolecular Polymers: Impact of Nanoparticles and Phase Separation on Printability.

3D printing of linear and three-arm star supramolecular polymers with attached hydrogen bonds and their nanocomposites is reported. The concept is based on hydrogen-bonded supramolecular polymers, known to form nano-sized micellar clusters. Printability is based on reversible thermal- and shear-induced dissociation of a supramolecular polymer network, which generates stable and self-supported structures after printing, as checked via melt-rheology and X-ray scattering. The linear and three-arm star poly(isobutylene)s PIB-B2 (Mn = 8500 g mol -1 ), PIB-B3 (Mn = 16 000 g mol -1 ), and linear poly(ethylene glycol)s PEG-B2 (Mn = 900 g mol-1 , 8500 g mol -1 ) are prepared and then probed by melt-rheology to adjust the viscosity to address the proper printing window. The supramolecular PIB polymers show a rubber-like behavior and are able to form self-supported 3D printed objects at room temperature and below, reaching polymer strand diameters down to 200-300 µm. Nanocomposites of PIB-B2 with silica nanoparticles (12 nm, 5-15 wt%) are generated, in turn leading to an improvement of their shape persistence. A blend of the linear polymer PIB-B2 and the three-arm star polymer PIB-B3 (ratio ≈ 3/1 mol) reaches an even higher structural stability, able to build free-standing structures.

Supramolecular Polymer Network-Mediated Structural Phase Transitions within Polymeric Micelles in Aliphatic Alcohols.

Self-complementary supramolecular polymers (SCSPs), an efficient combination of sextuple hydrogen-bonded dimer moieties and a temperature-responsive polymer, can promote the construction of stable supramolecular polymer networks (SPNs) that enable the formation of well-defined nanospherical micelles in aliphatic alcohols. These micelles undergo tailorable, thermoresponsive phase transitions at the upper critical solution temperature (UCST) and have a desirable spherical morphology and size ranges, thus, are potential candidates for applications in interfacial engineering and biomedical fields. Moreover, concentration-dependent UCST measurements and variable-temperature experiments indicated that the hydrogen-bonded complexes are strong enough to form stable intermolecularly entangled SPNs within the micelles, even above the UCST or at low concentrations in solution, which enables the micelles to undergo reversible temperature-dependent conformational changes between insoluble and soluble globules without significant changes in particle size or size distribution. Thus, this newly discovered system offers a new approach toward the development of next-generation temperature-responsive SCSPs with the desired structural stability that undergoes UCST transitions.

Toughening of Glassy Supramolecular Polymer Networks.

A modular approach for the design of two-component supramolecular polymer (SMP) networks is reported. A series of materials was prepared by blending two (macro)monomers based on trifunctional poly(propylene oxide) (PPO) cores that were end-functionalized with hydrogen-bonding 2-ureido-4[1H]pyrimidinone (UPy) groups. One monomer was based on a PPO core with a number-average molecular weight (Mn) of 440 g mol-1. The SMP formed by this building block is a glassy, brittle material with a glass transition temperature (Tg) of about 86 °C. The second monomer featured a PPO core with an Mn of 3000 g mol-1. The SMP formed by this building block adopts a microphase-segregated morphology that features a rubbery phase with a Tg of -58 °C and crystalline domains formed by the UPy assemblies, which act as physical cross-links and melt around 90-130 °C. Combining the two components allows access to microphase-segregated blends comprised of a rubbery phase constituted by the high-Mn cores, a glassy phase formed by the low-Mn component, and a crystalline phase formed by UPy groups. This allowed tailoring of the mechanical properties and afforded materials with storage moduli of 37-609 MPa, tensile strengths of 2.0-5.4 MPa, and melt viscosities of as low as 11 Pa s at 140 °C. The materials can be used as reversible adhesives.

Stimuli-responsive fluorescent supramolecular polymer network based on a monofunctionalized leaning tower[6]arene

A fluorescent supramolecular polymer network with an excellent triple-stimuli responsive property based on metal–ligand coordination and host–guest interactions has been constructed from a terpyridine-monofunctionalized leaning tower[6]arene, a tetraphenylethylene AIEgen, and a bridging coordination ion (Zn2+). Addition of competitive binding agents, trifluoroacetic acid, and/or pillar[5]arene can break the metal coordination and/or host-guest inclusion complexation, and thermal heating can weaken the non-covalent interactions in the supramolecular polymer gel, all leading to the gel-to-sol transition.

In Situ Generation of AgI Quantum Dots by the Confinement of A Supramolecular Polymer Network: A Novel Approach for Ultrasensitive Response.

A novel approach for in situ generation of AgI quantum dots by the confinement of a pillar[5]arene-based supramolecular polymer network has been successfully developed. The supramolecular polymer network (SPN-QP) was constructed by using a bis-8-hydroxyquinoline-modified pillar[5]arene derivative as a host (H-QP) and a bis-pyridinium-modified decane as guest (G-PD). The SPN-QP shows ultrasensitive response for Ag+ . The limit of detection is about 7.44×10-9 M.. Interestingly, when I- was added to the SPN-QP+Ag+ system, an unexpected strong warm-white fluorescence emission was observed. After carefu investigation, we found that the strong warm-white fluorescence emission could be attributed to the in situ formation of AgI quantum dots under the confinement of the supramolecular polymer network (SPN-QP). Based on this approach, ultrasensitive detection of I- was realized. The limit of detection for I- is 4.40×10-9 M. This study provides a new way for the preparation of quantum dots under the confinement of supramolecular polymer network as well as ultrasensitive detection of ions by in situ formation of quantum dots.

Recent advances in the physics of polymer systems

Recent advances in the physics of polymer systems

Spongy Materials Based on Supramolecular Polymer Networks for Detection and Separation of Broad-Spectrum Pollutants

By rationally introducing multi-interactions sites, supramolecular polymer networks (SPN-TDPG) has been successfully designed and constructed. SPN-TDPG gel shows aggregation-induced emission, meanw...

Efficient Aggregation-Induced Emission Manipulated by Polymer Host Materials.

Linear copolymer hosts bearing a number of pillar[5]arene dangling side chains are synthesized for the facile construction of highly emissive supramolecular polymer networks (SPNs) upon noncovalently cross-linking with a series of tetraphenyethylene (TPE)-based tetratopic guests terminated with different functional groups through supramolecular host-guest interactions. An extremely high fluorescence quantum yield (98.22%) of the SPNs materials is obtained in tetrahydrofuran (THF) by fine-tuning the parameters, and meanwhile supramolecular light-harvesting systems based on spherical supramolecular nanoparticles are constructed by interweaving 9,10-distyrylanthracene (DSA) and TPE-based guest molecules of aggregation-induced emission (AIE) with the copolymer hosts in the mixed solvent of THF/H2 O. The present study not only illustrates the restriction of the intramolecular rotations (RIR)-ruled emission enhancement mechanism regulated particularly by macrocyclic arene-containing copolymer hosts, but also suggests a new self-assembly approach to construct high-performance light-harvesting materials.

Fluoride-responsive debond on demand adhesives: Manipulating polymer crystallinity and hydrogen bonding to optimise adhesion strength at low bonding temperatures

This paper reports the solvent-free synthesis of a series of six fluoride responsive debond-on-demand polyurethane (PU) adhesives that contain a silyl functionalised degradable unit (DU). To optimise the adhesion strength and debonding nature of the adhesives, the chemical composition of the PUs was varied according to the structure of the polyol or the diisocyanate component in the polymer mainchain. 1H NMR spectroscopy was used to study the depolymerisation behaviour in solution state. It showed that tetra-butylammonium fluoride (TBAF) triggered the breakdown of the DU unit without fragmenting the polyol mainchain indiscriminately. On exposure to fluoride ions, the PUs underwent depolymerisation with reductions in Mn ranging from 64 to 90% as measured by GPC analysis. The morphology and thermal properties of the PUs were characterised by differential scanning calorimetry (DSC), rheology and variable temperature (VT) SAXS/WAXS analysis. Each technique demonstrated the reversibility of the supramolecular polymer network under thermal stimuli. PUs containing poly(butadiene) soft segments were amorphous with glass transition and viscoelastic transition temperatures dependent on the nature of the soft segment and diisocyanate starting materials. The PU containing a polyester soft segment exhibited a defined melting point at 49 °C. Mechanical stress-strain analysis of the series of PUs showed each exhibited greater than 70% reduction in toughness after treatment with TBAF for 30 min as a consequence of the chemo-responsive degradation of the polymer mainchain. The material featuring an ester-based polyol demonstrated excellent adhesion at bonding temperatures as low as 60 °C. Moreover, this material could be thermally rebonded if broken by force without loss in adhesion strength over three debond-rebond cycles. Lap shear adhesion tests showed a reduction in adhesive strength of approximately 40% (from 11.4 MPa to 7.3 MPa) on exposure to fluoride ions.

Deconvolution of the Effects of Binary Associations and Collective Assemblies on the Rheological Properties of Entangled Side-Chain Supramolecular Polymer Networks

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 o...