Four-arm Star Research Articles

Synthesis of Dendrimer-Like Molecules with Partial Carbon Chain via Iterative Single Unit Monomer Insertions.

Carbon-chain dendritic polymers hold unique properties and promising applications. However, synthesizing carbon-chain dendrimers, beyond conjugated ones, remains a challenge. Here, the use of the iterative single unit monomer insertion technique for synthesizing 2.5 generation partial-carbon-chain dendrimers (G2.5) is described, utilizing bismaleimide as the core, a maleimide-trithiocarbonate conjugate as the branching unit, and indene as the spacer unit, following a divergent growth strategy. The optimized conditions for synthesizing the maleimide-trithiocarbonate branching unit are a bismaleimide to trithiocarbonate ratio of 5:1 and a reaction time of 30 min. The structures are verified using 1H nuclear magnetic resonance, gel permeation chromatography, and matrix-assisted laser desorption/ionization-time of flight mass spectra. A four-arm star polymer is then synthesized using the G2.5 as the core. This synthesis of a partial-carbon-chain dendrimer establishes a foundational step toward creating all-carbon-chain ones and may open new application avenues in material science.

Star copolymers with tunable clusteroluminescence

Four-armed star copolymers with fluorescence emission from blue to red are synthesized through the RAFT polymerization method.

The effect of the polydimethylsiloxane chain length on the properties of four-arm siloxane stars

Five low-dispersity star-shaped polydimethylsiloxanes were synthesized. The macromolecules of the polymers contain the same branching-out center, a cis-tetraphenylcyclotetrasilsesquioxane moiety, and the same number of arms, but with different lengths (n = 15, 21, 48, 75, and 123 Si(Me)2O units). Their properties were studied by a set of physicochemical analytical methods. Viscometric studies showed that the macromolecules of the Ph4-15, Ph4-21, Ph4-48, and Ph4-75 polymers are small-sized dense balls both in solution and in melt. DSC studies identified an unusual effect of the cyclic core on the thermal behavior of the Ph4-15, Ph4-21, and Ph4-48 polymers. Its incorporation suppresses the crystallization of PDMS-arms (up to n = 48 Si(Me)2O units) at concentrations four times lower than those of known modifiers and does not affect the glass transition temperature (ca. -124 °С).

Practical compatibility between self-consistent field theory and dissipative particle dynamics

Self-consistent field theory (SCFT) and dissipative particle dynamics (DPD) simulations for the predicted microphase-separated structures of block copolymers (BCPs) are effective methods to reproduce behaviors at a scale larger than the Kuhn length. For linear chains, polymer-level correspondence at larger than the Kuhn length scale is maintained by their definition. For nonlinear polymer architectures, practical compatibility is expected to be governed by their natures originating from their architectures. Although the relation χ ≅ 0.306 Δa between the Flory–Huggins interaction parameter (χ) and segregation strength (Δa) for the mean structure at equilibrium is empirically accepted with a qualitative agreement for the large limit of polymerization-degree N, we need to verify the practicality of this relation in a chain of finite sizes and/or non-linear architectures for the recent advances of topology-controlled synthesis technology. We clarified the difference between the DPD and the conventional SCFT and the required improvements for a problem of the domain spacing D of the lamellar structures of symmetric AB-type BCPs of branched/star chains. For the four-arm star structure with H-shaped bonded star, SCFT should consider the particle-based H-shaped chains like DPD. Although the D values of SCFT agreed with that of DPD at the linear melts, the H-shaped bonded star melt presented a small discrepancy in the values of D; the discrepancy significantly decreased from the conventional SCFT for star chains with the point junction without considering H-shape. These understandings allow the prediction of D for BCPs synthesized with arbitrary topologies.

Model dynamic covalent thermoresponsive amphiphilic polymer co-networks based on acylhydrazone end-linked Tetronic T904 star block copolymers

Hydrogels based on acylhydrazone end-linked Tetronic T904 four-armed amphiphilic star block copolymers show thermally-induced aqueous self-assembly and toughening, and cross-link dissociation and association traceableviasimple1H NMR spectroscopy.

Emergence of Connected Binary Spherical Structures from the Self-assembly of an AB2C Four-Arm Star Terpolymer

Emergence of Connected Binary Spherical Structures from the Self-assembly of an AB₂C Four-Arm Star Terpolymer

Hydrodynamic interaction within star-branched macromolecules

Recent work arrived at expressions for the complex viscosity of a suspension of star-branched macromolecules [Coombs, Phys Fluids, 33, 093111 (2021)] using general rigid bead-rod theory without hydrodynamic interaction. In this work, we advance the theory by accounting for intramolecular interactions modeled with the interferences of Stokes flow solvent velocity profiles between adjacent beads. We derive the analytical expression for the complex viscosity of a suspension of four-arm star-branched macromolecules as a function of the number of beads in each arm NB and of the hydrodynamic interaction parameter A. We test our comprehensive theory against complex viscosity measurements of a cis-polybutadiene silicon-centered four-arm star suspension. We find the incorporation of hydrodynamic interaction improves the fit to complex viscosity measurements.

New Machine Learning Approach for the Optimization of Nano-Hybrid Formulations

Nano-hybrid systems are products of interactions between organic and inorganic materials designed and planned to develop drug delivery platforms that can be self-assembled. Poloxamine, commercially available as Tetronic®, is formed by blocks of copolymers consisting of poly (ethylene oxide) (PEO) and poly (propylene oxide) (PPO) units arranged in a four-armed star shape. Structurally, Tetronics are similar to Pluronics®, with an additional feature as they are also pH-dependent due to their central ethylenediamine unit. Laponite is a synthetic clay arranged in the form of discs with a diameter of approximately 25 nm and a thickness of 1 nm. Both compounds are biocompatible and considered as candidates for the formation of carrier systems. The objective is to explore associations between a Tetronic (T1304) and LAP (Laponite) at concentrations of 1–20% (w/w) and 0–3% (w/w), respectively. Response surface methodology (RMS) and two types of machine learning (multilayer perceptron (MLP) and support vector machine (SVM)) were used to evaluate the physical behavior of the systems and the β-Lapachone (β-Lap) solubility in the systems. β-Lap (model drug with low solubility in water) has antiviral, antiparasitic, antitumor, and anti-inflammatory properties. The results show an adequate machine learning approach to predict the physical behavior of nanocarrier systems with and without the presence of LAP. Additionally, the analysis performed with SVM showed better results (R2 > 0.97) in terms of data adjustment in the evaluation of β-Lap solubility. Furthermore, this work presents a new methodology for classifying phase behavior using ML. The new methodology allows the creation of a phase behavior surface for different concentrations of T1304 and LAP at different pHs and temperatures. The machine learning strategies used were excellent in assisting in the optimized development of new nano-hybrid platforms.

CuS-PNIPAm nanoparticles with the ability to initiatively capture bacteria for photothermal treatment of infected skin.

Copper sulfide nanoparticles (CuS NPs) have shown great potential in various application fields, especially in biomedical engineering fields. CuS NPs, with the ability to actively capture and kill bacteria and without the worry of biocompatibility, will greatly expand their applications. Herein, a four-arm star thermo-sensitive polyisopropylacrylamide (4sPNIPAm) was used to modify CuS NPs (CuS-PNIPAm NPs). The obtained NPs displayed the controlled release of copper ions and higher photothermal conversion ability in comparison with contrast materials CuS-PEG NPs and CuS NPs. Aggregation of CuS-PNIPAm NPs at above 34°C resulted in capturing bacteria by forming the aggregates of NPs-bacteria. Both Staphylococcus aureus and Escherichia coli co-cultured with CuS-PNIPAm NPs were completely killed upon near-infrared irradiation in minutes. Furthermore, CuS-PNIPAm NPs were verified to be a photothermal agent without toxic effect. In in vivo experiment, the NPs effectively killed the bacteria in the wound and accelerated the process of wound repairment. Overall, photothermal treatment by CuS-PNIPAm NPs demonstrates the ability to actively capture and kill bacteria, and has a potential in the treatment of infected skin and the regeneration of skin tissues. The therapy will exert a far-reaching impact on the regeneration of stubborn chronic wounds.

Synthesis and hydrodynamic properties of star poly(2-alkyl-2-oxazolines) and poly(2-alkyl-2-oxazines) based on sulfochlorinated calix[4]arene initiator

New four-arm star poly(2-alkyl-2-oxazolines) and poly(2-alkyl-2-oxazines) were synthesized using sulfochlorinated calix[4]arene derivative as a multifunctional initiator. Their characteristics were investigated by gel permeation chromatography, light scattering and viscometry. The polymer stars obtained were shown to have well-defined architecture and high intramolecular density.

Quantitative Luminescence Photography of a Swellable Hydrogel Dressing with a Traffic-Light Response to Oxygen.

Sensor-integrated wound dressings are emerging tools applicable to a wide variety of medical applications from emergency triage to at-home monitoring. Uncomfortable, unnecessary wound dressing changes may be avoided by providing quantitative insight into tissue characteristics related to wound healing such as tissue oxygenation, pH, and exudate/transudate volume. Here, a simple cost-effective methodology for quantifying oxygen and pH in a swellable hydrogel dressing using a single photograph is presented. The red and green luminescence of a novel dendritic polyamine Pt-porphyrin and fluorescein conjugate quantitatively responds to oxygen and pH, respectively, and enables robust sensing. The porphyrin conjugate, when combined with a four-arm star polyethylene glycol (PEG) amine polymer, rapidly crosslinks at room temperature with an N-hydroxysuccinimide (NHS)-PEG crosslinker to form a color-changing hydrogel dressing with tunable swelling capabilities applicable to a variety of wound environments. An inexpensive digital single-lens reflex (DSLR) camera modified with bandpass filters captures the hydrogel luminescence using simple macroscopic photography, and conversion to HSB colorspace allows for intensity-independent image analysis of the hydrogels' dual modality response. The hydrogel formulation exhibits a robust and validated visible red-orange-green "traffic light" spectrum in response to oxygen changes, regardless of swelling state, pH, or autofluorescence from skin, thereby enabling the clinician friendly naked-eyefeedback.

Correction: Double hydrophilic poly(ethylene glycol)-block-poly(dehydroalanine) four-arm star block copolymers: synthesis and solution behavior

Correction for ‘Double hydrophilic poly(ethylene glycol)-block-poly(dehydroalanine) four-arm star block copolymers: synthesis and solution behavior’ by Peter J. Mons et al., Polym. Chem., 2022, 13, 4298–4308, https://doi.org/10.1039/D2PY00579D.

Precise fabrication of porous polymer frameworks using rigid polyisocyanides as building blocks: from structural regulation to efficient iodine capture.

Porous materials have recently attracted much attention owing to their fascinating structures and broad applications. Moreover, exploring novel porous polymers affording the efficient capture of iodine is of significant interest. In contrast to the reported porous polymers fabricated with small molecular blocks, we herein report the preparation of porous polymer frameworks using rigid polyisocyanides as building blocks. First, tetrahedral four-arm star polyisocyanides with predictable molecular weight and low dispersity were synthesized; the chain-ends of the rigid polyisocyanide blocks were then crosslinked, yielding well-defined porous organic frameworks with a designed pore size and narrow distribution. Polymers of appropriate pore size were observed to efficiently capture radioactive iodine in both aqueous and vapor phases. More than 98% of iodine could be captured within 1 minute from a saturated aqueous solution (capacity of up to 3.2 g g−1), and an adsorption capacity of up to 574 wt% of iodine in vapor was measured within 4 hours. Moreover, the polymers could be recovered and recycled for iodine capture for at least six times, while maintaining high performance.

Design of Dynamic Soft Materials Utilizing Rotaxane’s Structural Characteristics (2)

The design, synthesis, and function of dynamic soft materials utilizing the rotaxane’s structural characteristics have collected much interests of polymer scientists. Directed toward the development of the dynamic soft materials based on the linear-branched polymer topology transformation, the various linear-branched polymer topology transformation systems were constructed by using the dynamic nature of the rotaxane’s components. The topology difference between the linear and branched polymers prepared in this work could be confirmed by the difference in hydrodynamic volume, crystallinity, and morphology. In particular, three-armed star polymer-type branched polymer was synthesized using living polymerization and polymer reaction for the arm and star polymer synthesis, while the star polymer showed clear morphological difference besides those in hydrodynamic volume and viscosity toward the corresponding linear counterpart. Four-armed star polymer having two rotaxane-linked polymer chains was synthesized for the study on the physical property difference from the linear counterpart prepared by the cleavage of the attractive interaction between the rotaxane components. The physical property difference between the star and linear polymers was explained by the difference in polymer topology. Reversible linear-branched polymer topology system was constructed by the introduction of N-methyl moiety on the ammonium salt moiety placed on the axle component of the crown ether-based rotaxane structure. These results suggest the possible development of the dynamic soft materials as the stimuli-responsive polymers based on the reversible polymer topology transformation through the rotaxane’s dynamic structural control.

Construction and evaluation of novel αvβ3 integrin ligand-conjugated ultrasmall star polymer micelles targeted glomerular podocytes through GFB permeation

As glomerular cells, podocytes are the last line of defense for glomerular filtration barriers (GFB) and play a critical role in chronic kidney disease (CKD). Podocyte-targeted drug delivery is a promising direction in the treatment of CKD. In this study, we constructed four-arm star polymers conjugated with a novel linear RWrNM peptide. And poly ε-caprolactone (PCL) hydrophobic core and brush poly (2-hydroxyethyl methacrylate) (PHEMA) hydrophilic shell were synthesized by ROP and SET LRP polymerization. The PHEMA modified by succinic anhydride was coupled with the novel linear RWrNM peptide, and then the PCL hydrophobic core was loaded with dexamethasone acetate (Dexac) to form micelles with stable dimensions. Our findings showed that the novel micelles had an ultrasmall particle size of 16–30 nm. We, for the first time, showed that the specific affinity of the novel linear RWrNM peptide to primary podocytes (24.9 ± 1.7 times of the free RhB uptake) through the αvβ3 integrin receptor mediation was comparable to that of B16F10 cells (24.4 ± 1.2 times of the free RhB uptake). In vivo studies showed that the novel ultrasmall micelles possessed a significant kidney-targeted effect, excellent podocyte colocalization effect, and GFB permeability at 49%–60 % in normal SD rats. Besides, the novel ultrasmall micelles decreased the plasma elimination half-life of Dexac to 1.62–2.09 h and showed good safety in vitro and in vivo. Both in vitro and in vivo results demonstrated the novel ultrasmall micelles could be used as a promising drug delivery strategy for actively targeted therapy of CKD.

Rapidly Thermoreversible and Biodegradable Polypeptide Hydrogels with Sol-Gel-Sol Transition Dependent on Subtle Manipulation of Side Groups.

Thermoreversible hydrogels are attractive materials for biomedical applications, but their applications are still limited by nonbiodegradability and/or slow temperature-dependent gel-to-sol transition rates. In this research, we prepared a range of amphiphilic diblock, triblock, and four-armed star block copolymers composed of poly(ethylene glycol) (PEG) and poly(γ-(2-(2-ethoxyethoxy)ethyl)-l-glutamate) (P(EEO2LG)) segments, which can form rapidly thermoreversible hydrogels at physiological temperature. Intriguingly, the obtained hydrogels can transform from gel to sol within 10-70 s in response to the temperature decrease from 37 to 0 °C. The thermosensitive sol-gel-sol transitions are markedly faster than previously reported thermoreversible PEG-poly(l-glutamate) derivative hydrogels with subtle differences in the side groups and a widely studied poly(d,l-lactide-co-glycolide)-b-PEG-b-poly(d,l-lactide-co-glycolide) (PLGA-PEG-PLGA) hydrogel that required a much longer time of 40∼150 min. Further investigation of the relationship between the hydrogel property and polymer structure is performed, and the self-assembly mechanisms of different copolymers are proposed. Cytotoxicity assays and subcutaneous degradation experiments reveal that the PEG/P(EEO2LG) block copolymers are biocompatible and biodegradable. The polypeptide hydrogel can therefore be used as a three-dimensional platform for facile cell culture and collection by regulating the temperature.

Versatile Bimolecular Ring-Closure Method for Cage-Shaped Polymers

A scalable bimolecular ring-closure method was reported to prepare cage-shaped polymers using a self-accelerating double-strain-promoted azide–alkyne click reaction (DSPAAC) as the cyclization reaction. The success of this method was illustrated by the formation of four-arm and six-arm cage-shaped polycaprolactone (PCL). The well-defined four-arm and six-arm star PCL with para-ether bonded 2,6-diisopropylphenyl azide terminal groups were prepared by a living ring-opening polymerization and an end group modification process. The four-arm and six-arm cage-shaped PCL were then produced by employing the small linkers containing two or three sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DIBOD) groups to cyclize the corresponding four-arm and six-arm star PCL precursors. By slowly feeding a concentrated star PCL solution into a small volume of small linker solution, the productivities were optimized as around 0.8 g/L/15 h for the formation of four-arm and six-arm cage-shaped PCL with purities above 70%.

Collapse of four-arm stars polyelectrolyte brushes under an electric field in the presence of trivalent salt coions

Langevin dynamics simulations were conducted to study the collapse of grafted partially charged 4-arm star chains onto the oppositely charged grafting electrode in the presence of trivalent salt coions. Simulation results reveal that the average charge fraction of the grafted star chains and the salt concentration play critical roles in the competitive adsorption of charged monomers and trivalent salt coions onto the oppositely charged electrode. For grafted star chains with relatively high charge fraction, charged monomers are the dominant species collapsing on the oppositely charged electrode with the emergence of charge reversal on the grafting electrode. At a low charge fraction such that the total amount of charges on a grafted star molecule is comparable to that of a trivalent salt coion, trivalent salt coions absorb more strongly onto the electrode than grafted stars even at very low salt concentration. It is found that at relatively low charge fraction of star chains, the addition of trivalent salt coions does not lead to charge overcompensation of the surface charges on the grafting electrode. The stretching of star brushes under an electric field in the presence of trivalent salt coions was also briefly investigated.

Magnetically Assembled Photonic Crystal Gels with Wide Thermochromic Range and High Sensitivity.

Thermochromic poly(N-isopropyl acrylamide) (PNIPAM) photonic crystal gels based on 1D magnetically assembling colloidal nanocrystal clusters have attracted much attention due to its convenient preparation process, striking color response, and good mechanical strength. However, there remain challenges to broaden the thermochromic range and improve the sensitivity for their iridescent color display. Here, a PNIPAM photonic gel with wide thermochromic range and high sensitivity is prepared by using four-arm star poly(ethylene glycol) acrylamide (PEGAAm) as cross-linker at appropriately reduced magnetic field strength as well as cross-linker content. PEGAAm improves the homogeneity of the microstructure in PNIPAM photonic gel and thus maintains the structure colors at a wide temperature range from room temperature to 44°C. The reduced magnetic field strength of 70Gs and low cross-linker content (the molar ratio of monomer to cross-linker of 300:1) lead to a large initial lattice spacing of the photonic gel and thus wide diffraction wavelength migration of 194nm. This optimized PNIPAM gel exhibits vivid iridescent colors from orange-red to indigo blue as temperature increases from 20 to 44°C with satisfactory repeatability. Therefore, it may be an ideal candidate for temperature sensors and displays with utility and accuracy such as low-temperature burns.

Can oppositely charged polyelectrolyte stars form a gel? A simulational study.

We present a Langevin molecular dynamics study of an equimolar mixture of monodispersed oppositely charged di-block four-armed polyelectrolyte stars. We used an implicit solvent coarse-grained representation of the polyelectrolyte stars, and varied the length of the terminal charged blocks that reside on each arm. By varying the polymer concentration, we computed PV diagrams and determined the free-swelling equilibrium concentration with respect to a pure water reservoir as a function of the charged block length. We investigated various structural properties of the resulting equilibrium structures, like the number of ionic bonds, dangling arms, isolated stars, and cluster sizes. The ionic bonds featured a broad distribution of the number of arms involved and also displayed a distribution of net charges peaked around the neutral ionic bond. Our main result is that for charged block length equal to 4 and 5 ionized beads the resulting macro-aggregate spans the box and forms a network phase. Furthermore, we investigated the restructuring dynamics of ionic bonds; the results suggested both short bond lifetimes and a high frequency of ballistic association/dissociation events. Bonds result strong enough to yield a stable gel phase, but they are still weak enough to allow network restructuring under thermal fluctuations.