Linear Poly Research Articles

Effect of branching in zwitterionic polymer brushes grafted from PES UF membrane surfaces via AGET-ATR(c)P

This research explored the relationship between the antifouling behavior of porous ultrafiltration (UF) membranes and linear or branched brushes adorning their surfaces. Polyethersulfone UF membranes were functionalized via one-pot lithiation/acylation to enable surface-initiated activators generated by electron transfer for atom transfer radical (co)polymerization of sulfobetaine methacrylate (SBMA) and N,N′-methylenebisacrylamide (MBAm). Changing the SBMA/MBAm ratio and polymerization time grafted brushes at different branching and thicknesses. Surface analyses verified differences in brush architecture and that the degree of grafting increased with grafting time – it was higher for linear brushes than branched ones. Colloidal probe lateral force atomic force microscopy (LFM) showed ideal hydration–lubrication propensity of the lower branching degree poly(SBMA-co-MBAm) over pristine, linear poly(SBMA), and higher branching poly(SBMA-co-MBAm)-grafted membranes. Sharp-tip LFM predicted a critical size of <15 nm for penetrating the branched brush layers. Fouling experiments with bovine serum albumin (∼10 nm) and dextran (∼18 nm) revealed that linear and branched modifications had significantly less fouling than the pristine membrane. An optimal degree of branching can limit foulant adsorption, but fouling could be enhanced if the polymers' hydration capacity was diminished relative to a less dense network. Fouling experiments with soluble microbial products further demonstrated the branched membrane's high antifouling activity.

Conformational Parameters and Hydrodynamic Behavior of Poly(2-Methyl-2-Oxazoline) in a Broad Molar Mass Range.

In this work, we report our results on the hydrodynamic behavior of poly(2-methyl-2-oxazoline) (PMeOx). PMeOx is gaining significant attention for use as hydrophilic polymer in pharmaceutical carriers as an alternative for the commonly used poly(ethylene glycol) (PEG), for which antibodies are found in a significant fraction of the human population. The main focus of the current study is to determine the hydrodynamic characteristics of PMeOx under physiological conditions, which serves as basis for better understanding of the use of PMeOx in pharmaceutical applications. This goal was achieved by studying PMeOx solutions in phosphate-buffered saline (PBS) as a solvent at 37 °C. This study was performed based on two series of PMeOx samples; one series is synthesized by conventional living cationic ring-opening polymerization, which is limited by the maximum chain length that can be achieved, and a second series is obtained by an alternative synthesis strategy based on acetylation of well-defined linear poly(ethylene imine) (PEI) prepared by controlled side-chain hydrolysis of a defined high molar mass of poly(2-ethyl-2-oxazoline). The combination of these two series of PMeOx allowed the determination of the Kuhn-Mark-Houwink-Sakurada equations in a broad molar mass range. For intrinsic viscosity, sedimentation and diffusion coefficients, the following expressions were obtained: η=0.015M0.77, s0=0.019M0.42 and D0=2600M-0.58, respectively. As a result, it can be concluded that the phosphate-buffered saline buffer at 37 °C represents a thermodynamically good solvent for PMeOx, based on the scaling indices of the equations. The conformational parameters for PMeOx chains were also determined, revealing an equilibrium rigidity or Kuhn segment length, (A) of 1.7 nm and a polymer chain diameter (d) of 0.4 nm. The obtained value for the equilibrium rigidity is very similar to the reported values for other hydrophilic polymers, such as PEG, poly(vinylpyrrolidone) and poly(2-ethyl-2-oxazoline), making PMeOx a relevant alternative to PEG.

Molecular Self-Assembled Ether-Based Polyrotaxane Solid Electrolyte for Lithium Metal Batteries

Poly(ethylene oxide) has been widely investigated as a potential separator for solid-state lithium metal batteries. However, its applications were significantly restricted by low ionic conductivity and a narrow electrochemical stability window (<4.0 V vs Li/Li+) at room temperature. Herein, a novel molecular self-assembled ether-based polyrotaxane electrolyte was designed using different functional units and prepared by threading cyclic 18-crown ether-6 (18C6) to linear poly(ethylene glycol) (PEG) via intermolecular hydrogen bond and terminating with hexamethylene diisocyanate trimer (HDIt), which was strongly confirmed by local structure-sensitive solid/liquid-state nuclear magnetic resonance (NMR) techniques. The designed electrolyte has shown an obviously increased room-temperature ionic conductivity of 3.48 × 10-4 S cm-1 compared to 1.12 × 10-5 S cm-1 without assembling polyrotaxane functional units, contributing to the enhanced cycling stability of batteries with both LiFePO4 and LiNi0.8Co0.15Al0.05O2 cathode materials. This advanced molecular self-assembled strategy provides a new paradigm in designing solid polymer electrolytes with demanded performance for lithium metal batteries.

Ordered mesoporous carbon encapsulated linear poly(ionic liquid)s enabling synergy effect of surface groups and ionic moieties for CO2 fixation under mild conditions

Carbon dioxide (CO2) fixation into value-added chemicals has attracted growing attention and one promising atom-efficient pathway is via the cycloaddition with three member-ring compounds like epoxides. Herein, we demonstrated that encapsulation of linear poly(ionic liquid)s (PILs) on ordered mesoporous carbon materials provides a facile and feasible approach towards environmental-friendly heterogeneous catalysts with high performance in CO2 cycloaddition with epoxides under mild conditions. A series of novel linear phenolic hydroxyl group functional imidazolium-based PILs synthesized from hydroxymethylation reaction between 4-(imidazol-1-yl)phenol-1-butyl-imidazolium iodide and formaldehyde was loaded on ordered mesoporous carbon FDU-15–600 derived from mesoporous phenolic resin. By virtue of controlling the initial polymerization temperature, the molecular weight of PILs was facilely modulated, reaching strong host–guest interaction during the PIL immobilization. Highly stable immobilized PIL species with spatial satisfaction of ionic moieties and surface groups were thus realized to enable a synergic CO2 conversion via cycloaddition with epoxides. The optimal catalyst exhibited high yield and stable recyclability by using atmospheric CO2 under metal-additive-solvent-free conditions and the activity surprisingly exceeded the corresponding homogeneous parent IL and PIL. Excellent substrate compatibility was found by extending the transformation of more than ten epoxides including the inert ones such as disubstituted cyclohexene oxide. The significantly enhanced activity is attributed to the synergistic effect of the surface hydrogen groups and ionic moieties to accelerate the rate-determining ring-opening process.

Thiol-epoxy 'click' chemistry: a focus on molecular attributes in the context of polymer chemistry.

Base-catalyzed ring-opening reaction of epoxides with the thiol nucleophiles is useful in the preparation and post-polymerization modification of synthetic polymers. Due to its many beneficial characteristics, this process is referred to as the thiol-epoxy 'click' reaction. In this article, our aim is to discuss the fundamental attributes of this process by tracing our own steps in the field. We initially address the aspects of efficiency, regio-selectivity, stoichiometry, and reaction conditions with the help of linear, hyperbranched, graft, dendritic, and cross-linked poly(β-hydroxy thioether)s. A special emphasis is placed on hydrogel synthesis and photopolymerization on surfaces. Subsequently, quenching of the alkoxide anion is considered which is a critical step in the formation of the β-hydroxy thioether linkage upon completion of reaction. The amenability of further reaction on the hydroxy and thioether groups through esterification and sulfur alkylation is then discussed. Initially, post-gelation/fabrication modification of sulfide linkages is considered to obtain cationic sulfonium hydrogels and zwitterionic photopatterned networks with antibacterial and antibiofouling properties, respectively. A post-synthesis functionalization strategy is then described to access same centered and segregated main-chain poly(β-hydroxy sulfonium)s as potent antibacterial materials. In side-chain polysulfides, the sequential post-synthesis modifications involving poly(glycidyl methacrylate) scaffolds can lead to the formation of amphiphilic homopolymers. The application of such materials is discussed in the arena of siRNA delivery. Finally, concerns relating to the formation of disulfide defects and open research goals such as study of the orthogonality of the reaction are addressed.

Crosslinking of poly(n-butyl acrylate)-POSS copolymers via dynamic urea exchange enables self-healing, reprocessing and shape recovery

In this contribution, we reported a novel approach to crosslink linear poly(n-butyl acrylate)-POSS copolymers via a dynamic urea exchange reaction.

Green synthesis of well-defined linear poly(hydroxyl thioether) direct from epoxide in water

Epoxides can be directly transformed into linear poly(hydroxyl thioether)s by cascade O–S ER/AAROP in water and open system under mild conditions.

Enzyme and pH dual responsive linear-dendritic block copolymer micelles based on a phenylalanyl-lysine motif and peripherally ketal-functionalized dendron as potential drug carriers.

Stimuli-responsive linear-dendritic block copolymers (LDBCs) have attracted significant research attention as novel drug carriers. We report here three generations of new enzyme and pH dual responsive linear-dendritic block copolymers (LDBCs) with a phenylalanyl-lysine (Phe-Lys) dipeptide linking hydrophilic linear poly(N-vinylpyrrolidone) (PNVP) and a hydrophobic peripherally ketal-functionalized dendron derived from 2,2'-bis(hydroxymethyl)propionic acid (bis-MPA). The LDBCs are synthesized via a combination of interchange of xanthates/reversible addition-fragmentation chain transfer (MADIX/RAFT) polymerization of N-vinylpyrrolidone (NVP) and "chain-first" strategy. Their structures are confirmed by 1H NMR spectra. The gel permeation chromatograph (GPC) analysis revealed that the LDBCs have a narrow molecular weight distribution (PDI ≤ 1.25). The amphiphilic LDBCs can self-assemble into spherical nanomicelles in aqueous solution. The presence of enzyme or/and the change of pH cause disassembly of micelles to release encapsulated cargos. The release rates of the guest molecules are faster in buffer solution at pH 5.0 than those upon the addition of the activating enzyme and can be fine-tuned by changing the generation of bis-MPA dendrons. The combination of enzyme and pH dual stimuli results in significantly accelerated and more complete release of the loaded hydrophobic guests. The cell viability assay confirmed the favorable biocompatibility until the LDBC micelle concentration reached 800 μg mL-1. These results indicate that the LDBCs can be considered as a good candidate for targeting drug delivery.

Dynamic self-assembly of supramolecular catalysts from precision macromolecules.

We show the emergence of strong catalytic activity at low concentrations in dynamic libraries of complementary sequence-defined oligomeric chains comprising pendant functional catalytic groups and terminal recognition units. In solution, the dynamic constitutional library created from pairs of such complementary oligomers comprises free oligomers, self-assembled di(oligomeric) macrocycles, and a virtually infinite collection of linear poly(oligomeric) chains. We demonstrate, on an exemplary catalytic system requiring the cooperation of no less than five chemical groups, that supramolecular di(oligomeric) macrocycles exhibit a catalytic turnover frequency ca. 20 times larger than the whole collection of linear poly(oligomers) and free chains. Molecular dynamics simulations and network analysis indicate that self-assembled supramolecular di(oligomeric) macrocycles are stabilized by different interactions, among which chain end pairing. We mathematically model the catalytic properties of such complex dynamic libraries with a small set of physically relevant parameters, which provides guidelines for the synthesis of oligomers capable to self-assemble into functionally-active supramolecular macrocycles over a larger range of concentrations.

Fascinating chiral information transfer to titania/silica from near to racemic compound self-organized from polyethyleneimine and tartaric acid.

In this work, chiroptical crystalline complexes of PEI/Tart (P/T) consisting of linear poly(ethylemeimine) (PEI) and an enantiomeric excess (ee) of tartaric acid (Tart) were used as chiral catalytic templates in the hydrolytic condensation of titanium bislactates and co-condensation of titanium bislactates and tetramethoxysilane for the preparation of chiral titania (TiO2) and chiral titania/silica (TiO2/SiO2) hybrid. Different from the general case of enantiopure templates excelling in chiral transformation when compared to enantiomeric excess ones, P/T systems with different enantiomer ratios exhibited each activity in the transformation of their chiral information to the resulting minerals titania and titania/silica. Especially, the P/T complexes with ee only by ±4% (D/L = 52/48 or 48/52), which is near the racemic state (D/L = 50/50), served as excellent chiral catalytic templates to generate chiroptical titania and titania/silica with mirror relation of the CD signals. By means of DSC, XRD, SEM and DRCD techniques, the crystalline complexes of PEI/Tart (P/T), the as-prepared TiO2@P/T and TiO2/SiO2@P/T, and the calcined TiO2 and TiO2/SiO2 were thoroughly investigated and the mechanism of the chiral transformation from the enantiomeric excess of P/T to minerals was proposed.

Amphiphilic random copolymers bearing linear poly(oxyethylene) side chains and lateral dendritic wedges: Synthesis and their emulsifying performances

In this study, we demonstrated nonaqueous macroemulsions stabilized by amphiphilic random copolymers exhibiting linear poly(oxyethylene) side chains and two-generation dendritic wedges along their backbones, which were synthesized by traditional radical random copolymerization of oligo (ethylene glycol) methyl ether methacrylate (POEGMA) with 2-methyl-2-((2-(4-methyl-1H-1,2,3-triazol-1-yl) ethoxy) carbonyl) propane-1,3-diylbis(2,2,5-trimethyl-1,3-dioxane-5-carboxylate)) methacrylate (MPDMA) in THF using AIBN as initiators. PPOEGMA-ran-PMPDMA copolymers containing different molar fractions of MPDMA monomer unit ranging from 0.28 to 0.65 were achieved through the adjustment of the feed ratio of monomer pairs during the copolymerization. Interfacial tension experiments revealed the critical micelle concentrations of PPOEGMA-ran-PMPDMA copolymers decreased with the increase of the contents of MPDMA monomer unit in copolymer chains. [Bmim][PF6]-in-toluene emulsions were subsequently prepared using amphiphilic PPOEGMA-ran-PMPDMA copolymers as macromolecular emulsifiers. The average size of the emulsion droplets showed an increasing tendency with the increase of the contents of MPDMA monomer unit in random copolymer chains. Under the otherwise identical conditions, the emulsifying performances of PPOEGMA-ran-PMPDMA copolymers were better than those of PPOEGMA-b-PMPDMA diblock copolymer counterparts judging from the size of the emulsion droplets and the stability of the emulsions.

Chemical Characterization of Leachables in Catheter Device.

Extractables or leachables of biomaterials or residues of additives used in the manufacturing process that are potentially released from a medical device may have an adverse effect on a patient. Chemical characterization of leachable chemicals and degradation products in a medical device is an important aspect of its overall biocompatibility assessment process, which helps to ensure that the therapeutical benefits exceed the potential biological risks associated with the use of the device or its components or materials. By evaluating the types and amounts of chemicals that may migrate from a device to a patient during clinical use, potential toxicological risks can be assessed. A semipolar solvent, 40% ethanol in water (v/v), an appropriate surrogate for blood and blood related substances, was used as an extraction medium to mimic the body fluid in contact with a medical device. The extraction was conducted at 37 °C for 24 h for limited exposure medical devices per ISO 10993-12:2021. From gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) analysis, leachable chemicals of polylactams, linear polyamides, cyclic polytetramethylene ether (PTME), poly(tetramethylene ether) glycol (PTMEG), cyclic and linear poly(tetramethylene ether) glycol adipate (PTMEGA), cyclic and linear poly(tetramethylene ether) glycol adipamide (PTMEGAA) were structurally elucidated. The workflow presented in this study was proven to be a successful approach for rapid extractable and leachable profiling and identification with confidence.

Enhancement of Energy Storage Performances in PMMA/PVDF Nanocomposites with Low Dielectric Bismuth Carbonate Nanosheets

Both high discharge energy density (Ud) and charge–discharge efficiency (η) for nanocomposites are crucial to the development and application of modern electronic devices. However, the large dielectric contrast and ferroelectric phase greatly limit the improvement of Ud and η of poly(vinylidene fluoride) (PVDF)-based nanocomposites. Herein, Bi2O2CO3 (simplified as BOC) nanosheets with low dielectric constant and wide bandgaps and linear poly(methyl methacrylate) (PMMA) were filled into PVDF by solution casting to fabricate x vol % BOC/PAPF (PAPF is short for PMMA/PVDF) nanocomposites. The contributions of BOC nanosheets and linear PMMA, especially for the BOC nanosheet, have been systematically studied. Both experimental and simulation results show that BOC nanosheet and PMMA could improve the breakdown strength and reduce the dielectric loss and leakage current of nanocomposites simultaneously, realizing Ud and η improvement at the same time. As a result, the 1.0 vol % BOC/PAPF nanocomposite shows the highest energy storage performance with Ud = 13.68 J/cm3 and η = 85.72%, which is much superior to PVDF. Therefore, this study might provide a proof-of-concept for constructing nanocomposites with excellent Ud and η concurrently.

Efficient gene transfection of suspension cells by highly branched poly(β-amino ester)

Suspension cells play a crucial role in many biological processes. However, compared to adherent cells, it is particularly challenging to introduce exogenous genes into suspension cells to regulate their biological functions with non-viral gene vectors, mainly due to the low cellular uptake and endosomal escape of polyplexes. Herein, to improve the interactions of polyplexes with cellular membranes, we design and synthesize highly branched poly(β-amino ester) (HPAE) via an “A2 + B4 + C2” Michael addition strategy. Results show that branching significantly increases DNA condensation of HPAE, cellular uptake and endosomal escape of HPAE/DNA polyplexes. In mast cells (MCs), HPAE exhibits up to 80-fold higher gene transfection efficiency compared to the corresponding linear poly(β-amino ester) (LPAE) and the leading commercial gene transfection reagents PEI25k, jetPEI, and Lipofectamine 3000, without causing obvious cytotoxicity. Our study establishes a reliable non-viral platform for efficient gene transfection of suspension cells.

Advanced materials based on montmorillonite modified with poly(ethylenimine) and poly(2-methyl-2-oxazoline): Experimental and DFT study

This work reports for the first time the ability of inorganic matrix Na-montmorillonite (Mt) to interact with two structurally similar but in term of charge different polymers: linear cationic poly(ethylenimine) (PEI) and non-ionic poly(2-methyl-2-oxazoline) (PMeOx). The effect of various polymer loadings on the interlayer structure and physico-chemical characteristics of composite materials was examined using experimental (XRD, IR, TA analysis) and ab initio Density Functional Theory (DFT) methods. The different charge characteristics of the polymers affected their intercalation into Mt. For PEI-Mt, almost complete exchange of Na+ with PEI cations was found, implying that the PEI chains interacted with the Mt interlayer surface electrostatically. In PMeOx-Mt, the content of Na+ remained the same as in Na-Mt, indicating that PMeOx chains adhered to the Mt surface by hydrogen bonds and/or van der Waals forces. The results showed that PEI could only be intercalated into Mt interlayers up to 100% of the cation exchange capacity (CEC) of Na-Mt; the resulting chains were adsorbed on the Mt outer surface. In contrast, unexpected and very high adsorption of PMeOx on Mt interlayer and outer surfaces, markedly exceeding the CEC of Na-Mt, was discovered for the first time. DFT calculations indicated that both polymers are anchored onto the basal surface of montmorillonite through moderate to weak Cp–Hp∙∙∙ Ob hydrogen bonds. Additional Np–Hp∙∙∙Ob hydrogen bonds in the PEI-Mt structure support the stability of this hybrid structure. Both the PMeOx-Mt and PEI-Mt models showed high stability.

Fenugreek (Trigonella foenum graecum) gum: A functional ingredient with promising properties and applications in food and pharmaceuticals—A review

AbstractFenugreek (Trigonella foenum graecum) is an annual plant belonging to the family Leguminosae or Fabaceae. The seeds of fenugreek contain 26.8% soluble fiber chemically identified as galactomannans with properties similar to soluble fiber of guar seeds and psyllium husk and so on. Galactomannans are biopolymers consisting of linear core poly (1,4)‐β‐D‐mannan backbone having varying degrees of D‐galactosyl substituents attached by 1,6‐glycosidic linkages. Different galactomannans derived from various legumes usually differ in molecular weight, ratio of mannose to galactose, and the mode and place of linkages of galactose moieties to the mannan backbone. Fenugreek gum has a galactose to mannose ratio of 1:1, showing the highest amount of galactose resulting in its highest water solubility compared with guar and locust bean gum. It suggested that the galactose and mannose moieties are linked uniformly in fenugreek gum resulting in maximum hydration and solubility. This M/G ratio affects the physicochemical properties of galactomannans and is inversely related to the solubility of gum. Galactomannans sterically stabilize the emulsions against flocculation and coalescence by getting adsorbed onto oil droplets. In addition to this, galactomannans are all found to exhibit some surface, interfacial, and emulsification activities. Because of these properties, it is preferred over other natural hydrocolloids as an excellent ingredient for various food applications. As a hydrocolloid, fenugreek gum provides texture, appeal, gelling, thickening, emulsifying, stabilizing, and encapsulating properties. In the present review, we summarized the extraction, purification, chemical, functional properties, molecular structure, thermal and rheological behavior of gum isolated from fenugreek seeds, and then vital application of this traditional source of hydrocolloids in food, pharmaceutical, and other industries.

Three-Dimensional Crosslinked PAA-TA Hybrid Binders for Long-Cycle-Life SiOx Anodes in Lithium-Ion Batteries.

The large volume expansion hinders the commercial application of silicon oxide (SiOx) anodes in lithium-ion batteries. Recent studies show that binders play a vital role in mitigating the volume change of SiOx electrodes. Herein, we introduce the small molecule tannic acid (TA) with high branching into the linear poly(acrylic acid) (PAA) binder for SiOx anodes. The three-dimensional (3D) crosslinked network with multiple hydrogen bonds is formed by the incorporation of abundant hydroxyl groups with unique carboxyl groups, which increases the interfacial adhesive strength with SiOx particles. As a consequence, SiOx electrodes based on the PAA-TA binder show an excellent cycling performance with a high specific capacity of 1025 mA h g-1 at 500 mA g-1 after 250 cycles. Moreover, the SiOx||NCM811 full cell exhibits a reversible capacity of 143 mA h g-1 corresponding to 87.4% capacity retention after 100 cycles.

Comparison of Cyclic and Linear Poly(lactide)s Using Small-Angle Neutron Scattering.

Small-angle neutron scattering (SANS) experiments were conducted on cyclic and linear polymers of racemic and l-lactides (PLA) with the goal of comparing chain configurations, scaling, and effective polymer-solvent interactions of the two topologies in acetone-d 6 and THF-d 8. There are limited reports of SANS results on cyclic polymers due to the lack of substantial development in the field until recently. Now that pure, well-defined cyclic polymers are accessible, unanswered questions about their rheology and physical conformations can be better investigated. Previously reported SANS experiments have used cyclic and linear polystyrene samples; therefore, our work allowed for direct comparison using a contrasting (structurally and sterically) polymer. We compared SANS results of cyclic and linear PLA samples with various microstructures and molecular weights at two different temperatures, allowing for comparison with a wide range of variables. The results followed the trends of previous experiments, but much greater differences in the effective polymer-solvent interaction parameters between cyclic and linear forms of PLA were observed, implying that the small form factor and hydrogen bonding in PLA allowed for much more compact conformations in the cyclic form only. Also, the polymer microstructure was found to influence polymer-solvent interaction parameters substantially. These results illustrate how the difference in polymer-solvent interactions between cyclic and linear polymers can vary greatly depending on the polymer in question and the potential of neutron scattering as a tool for identification and characterization of the cyclic topology.

Temperature/pH-Sensitive Double Cross-Linked Hydrogels as Platform for Controlled Delivery of Metoclopramide.

Novel double cross-linked (DC) hydrogels with pH-/temperature-sensitive properties were designed and developed. Therefore, linear pH-sensitive poly(methyl vinyl ether-alt-maleic acid) (P(VME/MA)) macromolecules were absorbed within a thermosensitive poly(N-isopropylacrylamide-co-hydroxyethylacrylamide)-hydrogel (PNH) and, subsequently, cross-linked together through a solvent-free thermal method. As a novelty, double cross-linked hydrogels were obtained from previously purified polymers in the absence of any solvent or cross-linking agent, which are generally harmful for the body. The new DC structures were characterized by FT-IR spectroscopy, SEM, swelling kinetic measurements, and mechanical tests. The resulting scaffolds exhibited interconnected pores and a flexible pattern, compared to the brittle structure of conventional PNH. The swelling kinetics of DC hydrogels were deeply affected by temperature (25 and 37 °C) and pH (7.4 and 1.2). Furthermore, the hydrogels absorbed a great amount of water in a basic environment and displayed improved mechanical properties. Metoclopramide (Met) was loaded within DC hydrogels as a model drug to investigate the ability of the support to control the drug release rate. The results obtained recommended them as convenient platforms for the oral administration of drugs, with the release of the largest part of the active principle occurring in the colon.

Self‐Healing Hydrogels by Metal Complexation of 2,6‐Bis(1,2,3‐triazol‐4yl)pyridine Functionalized Tetra‐Arm Star Poly(ethylene glycol)

AbstractThe fabrication of 2,6‐bis(1,2,3‐triazol‐4yl)pyridine (btp) based metallo‐supramolecular gels has been mainly focusing on organogels. Only recently, the synthesis and metallo‐supramolecular hydrogel formation of linear poly(ethylene glycol) (PEG) with multiple btp units in the main chain are reported. In this manuscript, metallo‐supramolecular hydrogels that are constructed using tetra‐arm star PEG‐modified with btp end‐groups upon complexation with transition metal ions are reported. This btp‐functionalized star‐PEG precursor is more easily accessible and more defined than the previously reported linear system while also yielding stronger hydrogels. The gelation is selectively induced by Ni2+ ions and strongly depended on the metal‐ligand ratio and polymer concentration. The successful formation of organogels can be induced selectively by Ni2+ or Fe2+ ion complexation in acetonitrile, which leads to the strongest complexes. The inability to form hydrogels with Fe2+ ions is ascribed to the partial oxidation of Fe2+ to Fe3+ ions in an aqueous solution. Furthermore, the optimal conditions for achieving self‐healing capabilities are also determined (i.e., 4 wt% polymer concentration and btp:Ni2+ molar ratio of 2:1) using rheology. The high strain resistance and fast self‐healing characteristics make these specific Ni2+ metallo‐supramolecular hydrogels a promising platform for materials design with potential applications in supramolecular chemistry, coordination chemistry, and catalysis.