Well-defined Nanoparticles Research Articles

Gaining Structural Control by Modification of Polymerization Rate in Ring-Opening Polymerization-Induced Crystallization-Driven Self-Assembly.

Polymerization-induced self-assembly (PISA) has become an important one pot method for the preparation of well-defined block copolymer nanoparticles. In PISA, morphology is typically controlled by changing molecular architecture and polymer concentration. However, several computational and experimental studies have suggested that changes in polymerization rate can lead to morphological differences. Here, we demonstrate that catalyst selection can be used to control morphology independent of polymer structure and concentration in ring-opening polymerization-induced crystallization-driven self-assembly (ROPI-CDSA). Slower rates of polymerization give rise to slower rates of self-assembly, resulting in denser lamellae and more 3D structures when compared to faster rates of polymerization. Our explanation for this is that the fast samples transiently exist in a nonequilibrium state as self-assembly starts at a higher solvophobic block length when compared to the slow polymerization. We expect that subsequent examples of rate variation in PISA will allow for greater control over morphological outcome.

Controlling Cation Distribution and Morphology in Colloidal Zinc Ferrite Nanocrystals.

This paper describes the first synthetic method to achieve independent control over both the cation distribution (quantified by the inversion parameter x) and size of colloidal ZnFe2O4 nanocrystals. Use of a heterobimetallic triangular complex of formula ZnFe2(μ3-O)(μ2-O2CCF3)6(H2O)3 as a single-source precursor, solvothermal reaction conditions, absence of hydroxyl groups from the reaction solvent, and the presence of oleylamine are required to achieve well-defined, crystalline, and monodisperse ZnFe2O4 nanoparticles. The size of the ZnFe2O4 nanocrystals increases as the ratio of oleic acid and oleylamine ligands to precursor increases. The inversion parameter increases with increasing solubility of the precursor in the reaction solvent, with the presence of oleic acid in the reaction mixture, and with decreasing reaction temperature. These results are consistent with a mechanism in which ligand exchange between oleic acid and carboxylate ligands bound to the precursor complex influences the degree to which the reaction produces a kinetically trapped or thermodynamically stable cation distribution. Importantly, these results indicate that preservation of the triangular Zn–O–Fe2 core structure of the precursor in the reactive monomer species is crucial to the production of a phase-pure ZnFe2O4 product and to the ability to tune the cation distribution. Overall, these results demonstrate the advantages of using a single-source precursor and solvothermal reaction conditions to achieve synthetic control over the structure of ternary spinel ferrite nanocrystals.

Engineering Noble Metal-like Bi onto Hierarchical SrWO4 for the Enhancement of Photocatalytic Activity

Solar-driven hydrogen production from water has attracted increasing attention due to sustainable H2 fuel generation with zero-emissions. However, the design of a photocatalyst without noble metals to enable efficient water splitting is still critical for practical applications. In this study, the hierarchical microspheres of SrWO4 assembled with well-defined metallic Bi nanoparticles were synthesized through mild hydrothermal aging. The resultant photocatalyst with optimum proportion exhibited the competitive performance of a high hydrogen-generation rate at 4.5 mmol·h−1·g−1, outperforming SrWO4 and Bi by factors of 2.0 and 2.4, respectively. Both the experimental characterization and active analysis revealed that the synergistic effect of noble metal-like behavior of Bi and their electron-sink capacity mainly contribute to boosting the overall photocatalytic efficiency. This work may provide advanced insights into the application of economical bismuth elements as co-catalysts, instead of noble metals, to improve photocatalytic efficiency in solar-fuel conversion and environmental remediation.

Self-Assembly of a Multifunction DNA Tetrahedron for Effective Delivery of Aptamer PL1 and Pcsk9 siRNA Potentiate Immune Checkpoint Therapy for Colorectal Cancer.

Compared with the traditional single therapy, nanomedicine has promoted a multimodal combination treatment for various carcinomas, especially the development of corresponding intelligent multifunctional biomaterials based on advanced DNA nanotechnology has great potential in cancer combination therapy. Herein, we describe a strategy to “backpack” aptamer PL1, which specifically binds to PD-L1 and Pcsk9 siRNA on well-defined DNA tetrahedral nanoparticles (TDNs) via DNA hybridization, which collectively contributes to the effective therapy for colorectal cancer (CRC). In addition, we designed a targeted TDN upon folic acid (FA) recognition, limiting its release to the sites of tumors where folic acid receptor (FAR) is encountered. Our results demonstrated that the TDN-FA/PL1/Pcsk9-siRNA could free immune cells to target CRC cells and attenuate 83.48% tumor growth in mouse models of CT26 CRC. Mechanically, the cancer-targeting FA guided TDN-FA/PL1/Pcsk9-siRNA into tumor cells, thereby ensuring that the aptamer PL1 could choke the mutual effects between PD-1 and PD-L1, followed by a 1.69-fold increase in T cell number and a 1.9-fold suppression of T cell activity by the PD-1/PD-L1 pathway, while Pcsk9 siRNA decreased Pcsk9 expression averagely to the extent of 65.13% and then facilitated intratumoral infiltration of cytotoxic T cells robustly with IFN-γ and Granzyme B expression. Our results reveal that the multifunctional TND-FA/PL1/Pcsk9-siRNA is effective and safe for CRC therapy, thereby expanding the application of DNA nanotechnology for innovative therapies of various cancers.

Linear and Star Block Copolymer Nanoparticles Prepared by Heterogeneous RAFT Polymerization Using an ω,ω-Heterodifunctional Macro-RAFT Agent.

Herein, an ω,ω-heterodifunctional macromolecular reversible addition-fragmentation chain transfer (macro-RAFT) agent containing two different RAFT end groups was synthesized and employed to mediate aqueous photoinitiated RAFT dispersion polymerization of a methacrylic monomer. Because of the different RAFT controllability of two RAFT end groups toward methacrylic monomers, the RAFT end group with good controllability dominated the polymerization while the other RAFT end group with poor controllability was unreacted, leading to the formation of linear block copolymers. Because of the unique structure of the linear block copolymers, a diverse set of block copolymer nanoparticles with rich RAFT groups at the interface of the hydrophilic corona/the hydrophobic core were successfully prepared. Finally, μ-A(BC)C miktoarm star block copolymer nanoparticles were prepared by RAFT seeded emulsion polymerization of an acrylic monomer, which enables the further morphological control over polymer nanoparticles. We believe that the utilization of an ω,ω-heterodifunctional macro-RAFT agent in heterogeneous RAFT polymerization will offer considerable opportunities for the rational synthesis of well-defined molecular architectures and polymer nanoparticles.

Cytotoxic Potential of Bio-Silica Conjugate with Different Sizes of Silver Nanoparticles for Cancer Cell Death

Well-defined silver nanoparticles were doped into bio-based amorphous silica (Ag-b-SiO2) with different silver contents (from 2 to 20 wt%) by a solvent-free procedure. The four as-synthetized samples were hydrogenated at 300 °C to ensure the formation of zero-valent Ag nanoparticles. The prepared samples were characterized by X-ray powder diffraction (XRD), elemental analysis, N2 sorption measurements, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM). The characterization data confirmed the formation of well-defined zero-valent silver nanoparticles in the range of 3–10 nm in the low-loading samples, while in high-loading samples, bulky particles of silver in the range of 200–500 nm were formed. The in vitro cytotoxic activities of the Ag-b-SiO2 samples were tested against the tumor cell lines of breast (MCF-7), liver (HepG2), and colon (HCT 116) over a concentration range of 0.01 to 1000 g. The prepared samples exhibited a wide range of cytotoxic activities against cancer cells. An inverse relationship was observed between the silver nanoparticles’ size and the cytotoxic activity, while a direct relationship between the silver nanoparticles’ size and the apoptotic cell death was noticed.

Electrospun Polymer Nanofibers with Antimicrobial Activity.

Nowadays, nanofibers with antimicrobial activity are of great importance due to the widespread antibiotic resistance of many pathogens. Electrospinning is a versatile method of producing ultrathin fibers with desired properties, and this technique can be optimized by controlling parameters such as solution/melt viscosity, feeding rate, and electric field. High viscosity and slow feeding rate cause blockage of the spinneret, while low viscosity and high feeding rate result in fiber discontinuities or droplet formation. The electric field must be properly set because high field strength shortens the solidification time of the fluid streams, while low field strength is unable to form the Taylor cone. Environmental conditions, temperature, and humidity also affect electrospinning. In recent years, significant advances have been made in the development of electrospinning methods and the engineering of electrospun nanofibers for various applications. This review discusses the current research on the use of electrospinning to fabricate composite polymer fibers with antimicrobial properties by incorporating well-defined antimicrobial nanoparticles (silver, titanium dioxide, zinc dioxide, copper oxide, etc.), encapsulating classical therapeutic agents (antibiotics), plant-based bioactive agents (crude extracts, essential oils), and pure compounds (antimicrobial peptides, photosensitizers) in polymer nanofibers with controlled release and anti-degradation protection. The analyzed works prove that the electrospinning process is an effective strategy for the formation of antimicrobial fibers for the biomedicine, pharmacy, and food industry.

ZIFs derived polyhedron with cobalt oxide nanoparticles as novel nanozyme for the biomimetic catalytic oxidation of glucose and non-enzymatic sensor

The global prevalence of diabetes makes it a significant work to develop flagship sensors in glucose monitoring technology. Particularly, exploring highly active nanocomposites as biomimetic catalysts for the enzymatic reaction of glucose is extremely attractive in non-enzymatic glucose sensing. Herein, nitrogen-doped hollow carbon nano-polyhedron implanted with Co3O4 nanoparticles (NHCN–Co3O4) was introduced as nanozyme for the catalytic oxidation of glucose. NHCN–Co3O4 was synthesized by a two-step redox carbonization of zeolitic imidazolate frameworks. Morphology and structure characterizations revealed that NHCN–Co3O4 was a rhombic nano-dodecahedron with hollow N-doped carbon frameworks. In the frameworks, well-defined Co3O4 nanoparticles were embedded. With highly porous N-doped graphitization structure and embedded Co3O4, NHCN–Co3O4 displayed a distinguished biomimetic catalysis towards the direct oxidation of glucose at a low onset potential of 0.30 V. The biomimetic catalysis of glucose oxidation at NHCN–Co3O4 was so efficient that a steady-state current signal could be established within 3 s. By using NHCN–Co3O4 as nanozyme, a brilliant non-enzymatic glucose sensor was developed with a very low detection limit of 0.2 μM and broad detection range from 1.0 μM to 32.0 mM. Besides, NHCN–Co3O4 sensor also displayed an effective anti-interference capability towards the simulated interfering species including small biomolecules, amino acids, and chloride ion. Furthermore, notable repeatability, reproducibility and long-term stability were also presented. Finally, the successful blood sugar detection in human serum strongly manifests the possible real application of NHCN–Co3O4 sensor.

Rational Direct Synthesis of RbMnFe Nanoparticles (RbMnFe = RbxMn[Fe(CN)6](2+x)/3·nH2O Prussian Blue Analogue).

In this paper, we report the chemical strategy followed to obtain, in a direct way, nanoparticles of the RbxMn[Fe(CN)6](x+2)/3·nH2O (RbMnFe) Prussian blue analogue with the aim of keeping the switching ability of this compound at the nanoscale. The switching properties come from a reversible electron transfer between the iron and manganese ions and depends on the rubidium content in the structure that has to be higher than 0.6. Despite the multifunctionality of this family of compounds and its interest in various applications, no systematic studies were performed to obtain well-defined nanoparticles. This paper relates to such an investigation. To draw relationship between size reduction, composition, and switching properties, a special attention was brought to the determination of the composition through elemental analysis and structure refinement of powder X-ray diffraction patterns together with infrared spectroscopy and elemental analysis. Several chemical parameters were explored to control both the size reduction and the composition following a direct synthetic approach. The results show that the smaller the particles, the lower the rubidium content. This observation might prevent the observation of switching properties on very small particles. Despite this antagonist effect, we achieved switchable particles of around 200 nm without any use of surfactant. Moreover, the size reduction is associated with the observation of the electron transfer down to 52% of rubidium in the nanoparticles against 64% in microparticles. This work is of particular interest in processing such nanoparticles into devices.

Dual-responsive drug release and fluorescence imaging based on disulfide-pillar[4]arene aggregate in cancer cells

The construction of multistimuli-responsive nanoaggregate has become one of the increasingly significant research topics in supramolecular chemistry. We herein reported the pH- and glutathione dual-responsive supramolecular assemblies fabricated by the disulfide-containing pillar[4]arene and tetraphenylethylene derivatives possessing different alkyl chains in length. Morphological characterization experiments showed the binary supramolecular assemblies formed well-defined nanoparticles, which could facilitate their endocytosis in cells. More remarkably, due to the compact nanostructures and the existence of acidifiable carboxyl group and bioreducible disulfide linkage in pillar[4]arene, the obtained nanoaggregates presented high drug-loading efficiency and sustained drug release behaviors, as well as the targeted fluorescence imaging ability in cancer cells. Thus, it can be envisioned that such microenvironment-adaptable supramolecular nanoassemblies featuring dual stimuli-responsiveness and fluorescence-imaging abilities may be developed as more appealing nanosystems for the therapy of refractory disease.

Water denitration over titania-supported Pt and Cu by combined photocatalytic and catalytic processes: Implications for hydrogen generation properties in a photocatalytic system

The present work provides a new approach to the water denitration process and a facile strategy of catalyst preparation for the efficient hydrogen generation. The main focus of the research reported here was nitrate removal from aqueous solutions and simultaneous hydrogen generation under UV-Vis-light irradiation. This is a very important aspect in case of practical applications, eliminating the external source of hydrogen. Aiming to get a deeper understanding on the role of surface structures (size and shape of nanoparticles) towards the reduction mechanism and to establish basic principles for an efficient process, Pt-Cu/TiO2 and Pt-Cu/TiO2 modified with well-defined Pt nanoparticles were employed. The synthesized materials were characterized using various physicochemical techniques and tested comparatively for: (i) nitrate catalytic reduction by hydrogen (dark reaction) and (ii) nitrate photocatalytic reduction by in-situ generated solar hydrogen. In order to enhance overall denitration reaction by combined photocatalytic and catalytic processes, photo-generated charges and in-situ generated H2 as reducing agent were used. Improvement of catalytic performances of nitrate hydrogenation reaction (~100% NO3¯ conversion) related to intimate contact between Pt and Cu was obtained. The in-situ generated H2 by water splitting over the studied catalysts reduces efficiently NO3¯ ions. Enhanced photocatalytic activity toward solar H2 production by deposited well-defined Pt nanoparticles (~10 nm) was achieved. In order to make possible decontamination of polluted waters using in-situ generated H2 under light exposure, the future optimization of such photo-catalytic systems looks promising.

Crystal Facet-Dependent Intrinsic Charge Separation on Well-Defined Bi 4 TaO 8 Cl Nanoplate for Efficient Photocatalytic Water Oxidation

The development of photocatalysts with wide spectral absorption and high charge separation efficiency has always been a pursued objective for photocatalytic solar energy conversion. Herein, we reported a wide-range visible-light-active Bi 4 TaO 8 Cl (BTOC) single crystal nanoplate with dominating {110} and {001} facets for enhancing the intrinsic charge separation efficiency. Insitu selective photodeposition of metals and metal oxides provides evidences of photogenerated electrons and holes spatially separated on {110} and {001} coexposed facets of BTOC, respectively. The intrinsic charge separation efficiency was demonstrated to be closely dependent on the crystal facets, which can be modulated by tuning the coexposed crystal facet ratio. Further surface modification of BTOC with suitable dual cocatalyst Ag and RuO x enables remarkable improvement of charge separation efficiency and photocatalytic water oxidation performance. Investigation by comparison between well-defined BTOC nanoplate and BTOC nanoparticles confirmed the significance of coexposed crystal facets for efficient spatial charge separation and the blocking of reverse reaction from Fe 2+ to Fe 3+ ions during water oxidation reaction, indicating that rational modulation of exposed crystal facets is significant for controlling the intrinsic charge separation efficiency on Bi 4 TaO 8 Cl photocatalyst for efficient photocatalytic water splitting.

Deposition of metallic silver from versatile amidinate precursors for use in functional materials

Silver (Ag) amidinate metal organic decomposition precursors of the type: [Ag2((ArN)2C(H))2] (Ar = 2,6-dimethylphenyl (1), 2,6-diethylphenyl (2) and 2,6-diisopropylphenyl (3)) have been used for the first time in the deposition of Ag films on glass with multiple functionalities with potential application in optical/biological sensors or for use in electronic circuitry. Precursors 1–3 were isolated from the reaction of silver acetate with the appropriate ligand in a 1:2 stoichiometry and were characterized by 1H and 13C{1H} NMR, thermal gravimetric analysis and single crystal X-ray diffraction for 2. Single-layer depositions at 200 °C on glass substrates via spin coating produced transparent (>90% transmittance) coatings, with well-defined Ag nanoparticles. Multi-layer depositions at 200 °C on glass had a metallic lustre and were found to be conductive ( ρ = 0.916–1.83 × 10−6 Ωm). All films were strongly adhered and displayed excellent coverage of the substrate. Ag films deposited from 1 to 3 were analysed by grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis and scanning electron microscopy, with optical properties determined by UV-Vis spectroscopy.

Interface Dynamics in Ag-Cu3P Nanoparticle Heterostructures.

Earth-abundant transition metal phosphides are promising materials for energy-related applications. Specifically, copper(I) phosphide is such a material and shows excellent photocatalytic activity. Currently, there are substantial research efforts to synthesize well-defined metal–semiconductor nanoparticle heterostructures to enhance the photocatalytic performance by an efficient separation of charge carriers. The involved crystal facets and heterointerfaces have a major impact on the efficiency of a heterostructured photocatalyst, which points out the importance of synthesizing potential photocatalysts in a controlled manner and characterizing their structural and morphological properties in detail. In this study, we investigated the interface dynamics occurring around the synthesis of Ag–Cu3P nanoparticle heterostructures by a chemical reaction between Ag–Cu nanoparticle heterostructures and phosphine in an environmental transmission electron microscope. The major product of the Cu–Cu3P phase transformation using Ag–Cu nanoparticle heterostructures with a defined interface as a template preserved the initially present Ag{111} facet of the heterointerface. After the complete transformation, corner truncation of the faceted Cu3P phase led to a physical transformation of the nanoparticle heterostructure. In some cases, the structural rearrangement toward an energetically more favorable heterointerface has been observed and analyzed in detail at the atomic level. The herein-reported results will help better understand dynamic processes in Ag–Cu3P nanoparticle heterostructures and enable facet-engineered surface and heterointerface design to tailor their physical properties.

Hydrodynamically driven self-assembly of lignin bowls and spheres by line-type micro-mixer

We report a strategy to continuously prepare lignin bowls and spheres using hydrodynamic flow in a simple line-type micro-mixer device. The kinetics of the non-equilibrium self-assembly of lignin was controlled by hydrodynamic shearing forces. It indicates that the convective-diffusive mixing and mass transfer of lignin macromolecules at the boundary of THF and water lamellar fluids are critical for the self-assembly of well-defined lignin nanoparticles. The shearing force of water on THF decreased with the decreasing of flow rate ratio (FRR) of water to THF from 30 to 7.5, resulting in an increase in lignin bowls yield from 20.9% to 54.7%. Furthermore, the diameter of lignin nanoparticles can be controlled from 100 to 550 nm by changing the flow rate. In addition, the diffusion coefficient of solvent also plays an imperative part in the self-assembly process. Under the same hydrodynamic conditions, solvents with higher diffusion coefficients generate more nanospheres.

Spray-Pyrolytic Tunable Structures of Mn Oxides-Based Composites for Electrocatalytic Activity Improvement in Oxygen Reduction

Hybrid nanomaterials based on manganese, cobalt, and lanthanum oxides of different morphology and phase compositions were prepared using a facile single-step ultrasonic spray pyrolysis (USP) process and tested as electrocatalysts for oxygen reduction reaction (ORR). The structural and morphological characterizations were completed by XRD and SEM-EDS. Electrochemical performance was characterized by cyclic voltammetry and linear sweep voltammetry in a rotating disk electrode assembly. All synthesized materials were found electrocatalytically active for ORR in alkaline media. Two different manganese oxide states were incorporated into a Co3O4 matrix, δ-MnO2 at 500 and 600 °C and manganese (II,III) oxide-Mn3O4 at 800 °C. The difference in crystalline structure revealed flower-like nanosheets for birnessite-MnO2 and well-defined spherical nanoparticles for material based on Mn3O4. Electrochemical responses indicate that the ORR mechanism follows a preceding step of MnO2 reduction to MnOOH. The calculated number of electrons exchanged for the hybrid materials demonstrate a four-electron oxygen reduction pathway and high electrocatalytic activity towards ORR. The comparison of molar catalytic activities points out the importance of the composition and that the synergy of Co and Mn is superior to Co3O4/La2O3 and pristine Mn oxide. The results reveal that synthesized hybrid materials are promising electrocatalysts for ORR.

Controlling the Fine Structure of Glycogen-like Glucan by Rational Enzymatic Synthesis.

Glycogen-like glucan (GnG), a hyperbranched glucose polymer, has been receiving increasing attention to generate synthetic polymers and nanoparticles. Importantly, different branching patterns strongly influence the functionality of GnG. To uncover ways of obtaining different GnG branching patterns, a series of GnG with radius from 22.03 to 27.06 nm were synthesized using sucrose phosphorylase, α-glucan phosphorylase (GP), and branching enzyme (BE). Adjusting the relative activity ratio of GP and BE (GP/BE) made the molecular weight (MW) distribution of intermediate GnG products follow two different paths. At a low GP/BE, the GnG developed from "small to large" during the synthetic process, with the MW increasing from 6.15 × 106 to 1.21 × 107 g/mol, and possessed a compact structure. By contrast, a high GP/BE caused the "large to small" model, with the MW reduction of GnG from 1.62 × 107 to 1.21 × 107 g/mol, and created a loose external structure. The higher GP activity promoted the elongation of external chains and restrained chain transfer by the BE to the inner zone of GnG, which would modulate the loose-tight structure of GnG. These findings provide new useful insights into the construction of structurally well-defined nanoparticles.

Tracking the phase changes in micelle-based NiGa nanocatalysts for methanol synthesis under activation and working conditions

The hydrogenation of CO2 into high energy density fuels such as methanol, where the required H2 is obtained from renewable sources, is of utmost importance for a sustainable society. In recent years, NiGa alloys have attracted attention as promising catalyst material systems for the hydrogenation of CO2 into methanol at ambient pressures. They thus represent an energy-saving alternative to the Cu-based catalysts employed in today’s catalytic industry that require high pressures for the CO2 hydrogenation. However, the underlying reaction mechanisms for the NiGa system are still under debate. One of the challenges here is to unravel the evolution and coexistence of the different species in the heterogeneous NiGa catalyst system under activation and reaction conditions. To shed light on their evolution under activation in H2 and their catalytic roles under CO2 hydrogenation working conditions on well-defined Ni3Ga1 and Ni5Ga3 nanoparticle (NP) catalysts, we employed a multi-probe approach. It included advanced machine learning-based analysis of operando X-ray absorption spectroscopy data combined with operando powder X-ray diffraction and near ambient pressure X-ray photoelectron spectroscopy measurements, as well as reactivity studies using bed-packed mass flow reactors. In addition, we employed atomic force microscopy and scanning transmission electron microscopy for structural characterization.Under H2 activation at 1 bar total pressure, we concluded the formation of metallic Ni, starting for Ni3Ga1 at 300 °C, and for Ni5Ga3 at 400 °C. At higher temperatures, the formation of NiGa alloys follows. The α’-Ni3Ga1 alloy phase is predominantly formed for the Ni3Ga1 NPs, while the coexistence of α’-Ni3Ga1, δ-Ni5Ga3 and Ga2O3 phases is observed for the Ni5Ga3 NPs after the H2 activation. The formation of the Ga2O3 phase also results in the presence of excess metallic Ni. Under CO2 hydrogenation reaction conditions, Ga partially oxidizes again to form a Ga2O3-rich particle shell for both NP compositions, yet, to a larger extent for the Ni3Ga1 NPs, which, in turn, feature a higher amount of excess Ni. We reveal that metallic Ni is responsible for the high selectivity of the Ni3Ga1 NPs towards the production of methane in our catalytic tests. In contrast, the Ni5Ga3 NPs display a strong selectivity toward methanol production (>92%), more than one order of magnitude higher than that for the Ni3Ga1 NPs, which we ascribe to the presence of the δ-Ni5Ga3 phase.

Polymer-Grafted Nanoparticles (PGNs) with Adjustable Graft-Density and Interparticle Hydrogen Bonding Interaction.

Polymer-grafted nanoparticles (PGNs) receive great attention because they possess the advantages of both the grafted polymer and inorganic cores, and thus demonstrate superior optical, electronic, and mechanical properties. Thus, PGNs with tailorable interparticle interactions are indispensable for the formation of a superlattice with a defined and ordered structure. In this work, the synthesis of PGNs is reported which can form interparticle hydrogen-bonding to enhance the formation of well-defined 2D nanoparticle arrays. Various polymers, including poly(4-vinyl pyridine) (P4VP), poly(dimethyl aminoethyl acrylate) (PDMAEMA), and poly(4-acetoxy styrene) (PAcS), are attached to silica cores by a "grafting from" in a mini emulsion-like synthesis approach. SiO2 -PAcS brushes are deprotected by hydrazinolysis and converted into poly(4-vinyl phenol) (PVP), containing hydroxyl groups as potential hydrogen-bonding donor sites. Understanding and controlling interparticle interactions by varying grafting density in the range of 10-2 -10-3 chain nm-2 , and the formation of interparticle hydrogen bonding relevant for self-assembly of PGNs and potential formation of PGN superlattice structures are the motivations for this study.

Polyphosphonate-Based Macromolecular RAFT-CTA Enables the Synthesis of Well-Defined Block Copolymers Using Vinyl Monomers.

Reversible addition-fragmentation chain transfer (RAFT) polymerization has become a straightforward approach to block copolymers using a wide variety of functional vinyl monomers. Polyphosphoester (PPE) macroinitiators from ring-opening polymerization (ROP) of their corresponding cyclic phosphoesters have been previously prepared for atom transfer radical polymerization; however, to date, these biodegradable macroinitiators for RAFT polymerization have not been reported. Herein, a macromolecular RAFT-chain transfer agent (CTA) based on poly(ethyl ethylene phosphonate) was prepared by the organocatalytic ROP of 2-ethyl-2-oxo-1,3,2-dioxaphospholane using 2-cyano-5-hydroxypentan-2-yl dodecyl trithiocarbonate as the initiator and 1,8-diazabycyclo[5.4.0]undec-7-ene as the catalyst. Precise macro-CTAs of degrees of polymerization (DPn) from 34 to 70 with Đ ≤ 1.10 were prepared and used in the dioxane solution RAFT polymerization of acrylamide, acrylates, methacrylates, and 2-vinylpyridine to yield a library of well-defined block copolymers. Additionally, the PPE-based macro RAFT-CTA was used as a nonionic surfactant in a typical aqueous emulsion polymerization of styrene to produce well-defined nanoparticles with the hydrophilic PPEs on their surface as the stabilizing agent. This general protocol allowed the combination of polyphosphoesters with RAFT polymerization.