Influence of poly(ethylene glycol) block length on the adsorption of thermoresponsive copolymers onto gold surfaces

The adsorption of a series of four poly(N-isopropylacrylamide)-based copolymers composed of a hydrophilic block of methoxy poly(ethylene glycol) (MPEG) with a variable length and a PNIPAAM block of fixed size (MPEG _n -b-PNIPAAM₇₁) onto flat and spherical citrate-coated gold surfaces has been investigated. The adsorption onto planar surfaces was studied by means of the quartz crystal microbalance with dissipation monitoring, whereas polymer adsorption onto gold nanoparticles was examined using dynamic light scattering and visible spectroscopy. Experiments were performed with two different concentrations of polymer in bulk solution, namely 0.05 and 0.0005 wt%. The influence of the MPEG length on the thickness of the adsorbed layer on the nanoparticles, and the adsorbed mass onto the planar surfaces were recorded at different temperatures.     

Amphiphilic Block Copolymers Directed Interface Coassembly to Construct Multifunctional Microspheres with Magnetic Core and Monolayer Mesoporous Aluminosilicate Shell

Core–shell magnetic porous microspheres have wide applications in drug delivery, catalysis and bioseparation, and so on. However, it is great challenge to controllably synthesize magnetic porous microspheres with uniform well‐aligned accessible large mesopores (>10 nm) which are highly desired for applications involving immobilization or adsorption of large guest molecules or nanoobjects. In this study, a facile and general amphiphilic block copolymer directed interfacial coassembly strategy is developed to synthesize core–shell magnetic mesoporous microspheres with a monolayer of mesoporous shell of different composition (FDUcs‐17D), such as core–shell magnetic mesoporous aluminosilicate (CS‐MMAS), silica (CS‐MMS), and zirconia‐silica (CS‐MMZS), open and large pores by employing polystyrene‐block‐poly (4‐vinylpyridine) (PS‐b‐P4VP) as an interface structure directing agent and aluminum acetylacetonate (Al(acac)₃), zirconium acetylacetonate, and tetraethyl orthosilicate as shell precursors. The obtained CS‐MMAS microspheres possess magnetic core, perpendicular mesopores (20–32 nm) in the shell, high surface area (244.7 m² g^?1), and abundant acid sites (0.44 mmol g^?1), and as a result, they exhibit superior performance in removal of organophosphorus pesticides (fenthion) with a fast adsorption dynamics and high adsorption capacity. CS‐MMAS microspheres loaded with Au nanoparticles (≈3.5 nm) behavior as a highly active heterogeneous nanocatalyst for N‐alkylation reaction for producing N‐phenylbenzylamine with a selectivity and yields of over 90% and good magnetic recyclability.     

Preparation of silver nanocomposites stabilized by an amphiphilic block copolymer under ultrasonic irradiation

Silver nanoparticles were synthesized by using amphiphilic block copolymer Polyacrylonitrile-block-poly(ethylene glycol)-blcok-Polyacrylonitrile (PAN-b-PEG-b-PAN, PEA) based on the flexibility of the copolymer chains and the complex effect of –CN in the polyacrylonitrile with Ag⁺ ion and Ag under ultrasonic irradiation. The product was characterized by X-ray Diffraction (XRD), Fourier Transfer Infrared Spectrometer (FTIR), Transmission Electron Microscope (TEM), UV–Vis spectrum and Thermal Gravity Analysis (TGA). The results revealed that the size and size distribution of the resulting silver nanoparticles prepared basing on the copolymer were strongly dependent on the initial concentration of the silver ion solution and the irradiation conditions. Low initial silver ion concentration allowed for yielding silver nanoparticles with a small size and the size of the silver nanoparticles increased with increasing of silver ion concentration. The silver crystal was polycrystalline with a cubic structure, as confirmed by XRD. This work provides a simple route for the in situ synthesis of Ag nanoparticles.     

Preparation and characterization of Mn-Zn ferrite/poly(N,N′-isopropyl acrylamide) core/shell nanocomposites via in-situ polymerization

A kind of thermosensitive core/shell nanoparticles Mn-Zn ferrite/poly N,N′-isopropylacrylamide is designed in this work. By using surface initiated reversible addition-fragmentation chain transfer (RAFT) polymerization, thermoresponsive poly(N,N′-isopropylacrylamide) (PNIPAAm) was successfully covalently grafted from ferrite core. The graft polymerization exhibited the characteristics of a controlled/“living” polymerization which demonstrated a well controlled molecular weight. The nanoparticles obtained were also characterized by FTIR and HRTEM. FTIR results confirmed the successful graft polymerization, whereas HRTEM observation showed clearly a contrast between an ordered crystalline core and a light amorphous polymeric coating. With combined magnetic and thermosensitive properties, it could potentially be used as an anticancer drug carrier in biomedical field.     

Preparation and characterization of PNIPAAm-b-PLA/Fe3O4 thermo-responsive and magnetic composite micelles

Novel magnetic micelles with the flowerlike morphology were prepared with Fe₃O₄ nanoparticles and poly(N-isopropylacrylamide)-block-polylactide (PNIPAAm-b-PLA) copolymers by a dialysis method. The diameter of flowerlike micelles was about 1 μm. The core and shell of the micelles were hydrophilic, while the other area of the micelles was hydrophobic. The lower critical solution temperature (LCST) of PNIPAAm-b-PLA was about 38 °C. The magnetic intensity of Fe₃O₄ nanoparticles decreased after they were encapsulated into PNIPAAm-b-PLA micelles. Thermo-responsive and magnetic properties of the micelles would provide useful applications in the target drug delivery and release system.     

Biodegradable amphiphilic block-graft copolymers based on methoxy poly(ethylene glycol)-b-(polycarbonates-g-polycarbonates) for controlled release of doxorubicin

In this paper, novel biodegradable amphiphilic block-graft copolymers based on methoxy poly(ethylene glycol)-b-(polycarbonates-g-polycarbonates) (mPEG-b-(PATMC-g-PATMC)) were synthesized successfully for controlled release of doxorubicin (DOX). Backbone block copolymer, methoxy poly(ethylene glycol)-b-poly(5-allyloxy-1,3-dioxan-2-one) (mPEG-b-PATMC) was synthesized in bulk catalyzed by immobilized porcine pancreas lipase (IPPL). Then, mPEG-b-PATMC-O, the allyl epoxidation product of mPEG-b-PATMC, was further grafted by PATMC itself also using IPPL as the catalyst. The copolymers were characterized by ¹N HMR and gel permeation chromatography results showed narrow molecular weight distributions. Stable micelle solutions could be prepared by dialysis method, while a monomodal and narrow size distribution could be obtained. Transmission electron microscopy (TEM) observation showed the micelles dispersed in spherical shape with nano-size before and after DOX loading. Compared with the block copolymers, the grafted structure could enhance the interaction of polymer chains with drug molecules and improve the drug-loading capacity and entrapment efficiency. Furthermore, the amphiphilic block-graft copolymers mPEG-b-(PATMC-g-PATMC) had low cytotoxicity and more sustained drug release behavior.     

Synthesis of a thermoresponsive platinum nanocomposite using a three-layer onion-like polymer as template

Using a well-designed three-layer onion-like polymer as template, a one-pot procedure that led to stable, narrow-sized and thermoresponsive Pt nanocomposites is described. The polymer consists of an outer shell of thermoresponsive poly(N-isopropylacrylamide), an inner shell of crosslinked poly(N,N-dimethylaminoethyl acrylate) and a hyperbranched polyglycerol core. The core is physically trapped by the shell, with a few thiol groups located on the interface between the core and the shell. The polymer is used as a template for the synthesis of platinum nanoparticles, ¹H NMR and TEM analyses suggest that the in-situ produced, narrow-sized Pt nanoparticle is loaded in the core part of the polymer so that the nanocomposite retains thermoresponsive activity.     

Synthesis and catalysis of Ag nanoparticles trapped into temperature-sensitive and conductive polymers

Poly(styrene-co-N-isopropylacrylamide)/poly(N-isopropylacrylamide-co-methacrylic acid)/polypyrrole-silver [P(St-NIPAM)/P(NIPAM-co-MAA)/PPy-Ag] composite microgels were synthesized via a one-step redox polymerization of silver ammonia ions and pyrrole monomer at room temperature, using the core–shell P(St-NIPAM)/P(NIPAM-co-MAA) thermo-sensitive polymer microgels as templates. The structure, component, and properties of the as-prepared composite microgels have been characterized by transmission electron microscope, Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and UV–Vis spectrophotometer. The results indicate that the size and the dispersity of the formed PPy-Ag nanocomposite particles can be regulated by adjusting the initial concentration of the precursors. The catalytic activity for the reduction of 4-nitrophenol was regulated by varying the environment temperature. Meanwhile, the higher catalytic activity is contributed to the electron transfer from the conductive polymer PPy to the Ag nanoparticles in the polymer material matrix.     

Surface Engineering of Spherical Metal Nanoparticles with Polymers toward Selective Asymmetric Synthesis of Nanobowls and Janus‐Type Dimers

New synthetic methods capable of controlling structural and compositional complexities of asymmetric nanoparticles (NPs) are very challenging but highly desired. A simple and general synthetic approach to designing sophisticated asymmetric NPs by anisotropically patterning the surface of isotropic metallic NPs with amphiphilic block copolymers (BCPs) is reported. The selective galvanic replacement and seed‐mediated growth of a second metal can be achieved on the exposed surface of metal NPs, resulting in the formation of nanobowls and Janus‐type metal–metal dimers, respectively. Using Ag and Au NPs tethered with amphiphilic block copolymers of poly(ethylene oxide)‐block‐polystyrene (PEO‐b‐PS), anisotropic surface patterning of metallic NPs (e.g., Ag and Au) is shown to be driven by thermodynamical phase segregation of BCP ligands on isotropic metal NPs. Two proof‐of‐concept experiments are given on, i) synthesis of Au nanobowls by a selective galvanic replacement reaction on Janus‐type patched Ag/polymer NPs; and ii) preparation of Au–Pd heterodimers and Au–Au homodimers by a seed‐mediated growth on Janus‐type patched Au/polymer NPs. The method shows remarkable versatility; and it can be easily handled in aqueous solution. This synthetic strategy stands out as the new methodology to design and synthesis asymmetric metal NPs with sophisticated topologies.     

Preparation and properties of a novel thermo-responsive poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) hydrogel containing glycyrrhetinic acid

A novel thermo-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel containing glycyrrhetinic acid(GA) was synthesized by free radical copolymerization. The structure of the product was confirmed by FT-IR and ¹H-NMR spectra. The temperature responsibility and swelling properties of the copolymerized hydrogel were investigated by differential scanning calorimetry (DSC) and gravimetric methods. The results indicated that GA-incorporated hydrogel was still temperature responsive and the swelling ratio decreased with the increasing of temperature. The lower critical solution temperature (LCST) of GA-incorporated hydrogel and poly(N-isopropylacrylamide) hydrogel was 30.00 °C and 31.21 °C, respectively, in distilled water. However, these two values were shifted to 28.22 °C and 29.16 °C in cell culture media. The novel hydrogel also exhibited reversible temperature responsibility. Deswelling kinetics indicated that the copolymerized hydrogel deswelled more rapidly than poly(N-isopropylacrylamide) hydrogel. Since GA has specific binding capacity to asialoglycoprotein receptors on the membrane of hepatocyte, this novel hydrogel with GA could be expected as good candidate for hepatic cell culture.     

Synchronous delivery systems composed of Au nanoparticles and stimuli-sensitive diblock terpolymer

A method to construct synchronous delivery systems via direct self-assembly of Au nanoparticles on the poly[(N-isopropylacrylamide-r-acrylamide)-b-L-lactic acid] (PNAL) nanospheres has been presented in this paper. To achieve amphiphilic diblock terpolymer, hydrophobic poly (L-lactic acid) (PLLA) block was added to poly(N-isopropylacrylamide- r-acrylamide) (PNA) block via Michel-type addition reaction. Lower critical solubility temperature (LCST) was modulated at 35.6 °C which is close to the body temperature, but higher than poly(N-isopropylacrylamide) (PNIPAAm) homopolymer by controlling the ratio between isopropylacrylamide (IPAAm) monomers and acrylamide (AAm) monomers. Using this amphiphilic diblock terpolymer, PNAL nanospheres were fabricated by emulsion/evaporation technique followed by direct self-assembly of Au nanoparticles on the PNAL nanospheres due to the high affinity of amino groups donated from PNA block. The core site of Au@PNAL nanospheres can load various lyphophilic drugs. Moreover, Au nanoparticles in the shell domain of PNAL nanospheres give optimal environment to conjugate various biomolecules. Therefore, it is expected that Au@PNAL hybrid nanospheres can be utilized in synchronous delivery of both biomolecules in the shell domain and various therapeutic drugs in the core domain.     

Nanostructured physical gel of SBS block copolymer and Ag/DT/SBS nanocomposites

Thermoreversible physical gels of poly(styrene-b-butadiene-b-styrene) (SBS), formed by the dissolution of the block copolymer in a mid-block-selective solvent (THF), have been studied and characterized with particular attention to their morphology and rheological behavior. The effects of the addition of silver (Ag) nanoparticles to the SBS matrix, on the behavior of the physical gels, were also studied. The external surface of the Ag nanoparticles has been modified by using as surfactant material, dodecanethiol, in order to achieve their confinement in just one block of the SBS block copolymer matrix. The results of this study show that the gel stability is not affected by the presence of Ag nanoparticles. In fact, the micellar domains of the nanocomposite gel based on SBS block copolymer and Ag nanoparticles has been obtained and the physical gel behavior have been confirmed by rheological analysis.     

Preparation and characterization of poly(N-isopropylacrylamide) films on a modified glass surface via surface initiated redox polymerization

A functionalization with 3-aminopropyltriethoxysilane (APTES) monolayer of a hydroxylated glass surface, followed by the surface initiated graft radical polymerization of N-isopropylacrylamide (NIPAm) using amino groups of APTES monolayer chemical bonded with glass surface and Ce⁴⁺ as a redox initiating system. The microstructure of poly(N-isopropylacrylamide) (PNIPAm) film obtained from the redox graft polymerization on the modified glass surfaces was examined by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM), and the results showed that about 60 nm thickness of thermosensitive polymer (PNIPAm) film successfully formed.     

Stimuli‐Responsive,Shape‐Transforming Nanostructured Particles

Development of particles that change shape in response to external stimuli has been a long‐thought goal for producing bioinspired, smart materials. Herein, the temperature‐driven transformation of the shape and morphology of polymer particles composed of polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymers (BCPs) and temperature‐responsive poly(N‐isopropylacrylamide) (PNIPAM) surfactants is reported. PNIPAM acts as a temperature‐responsive surfactant with two important roles. First, PNIPAM stabilizes oil‐in‐water droplets as a P4VP‐selective surfactant, creating a nearly neutral interface between the PS and P4VP domains together with cetyltrimethylammonium bromide, a PS‐selective surfactant, to form anisotropic PS‐b‐P4VP particles (i.e., convex lenses and ellipsoids). More importantly, the temperature‐directed positioning of PNIPAM depending on its solubility determines the overall particle shape. Ellipsoidal particles are produced above the critical temperature, whereas convex lens‐shaped particles are obtained below the critical temperature. Interestingly, given that the temperature at which particle shape change occurs depends solely on the lower critical solution temperature (LCST) of the polymer surfactants, facile tuning of the transition temperature is realized by employing other PNIPAM derivatives with different LCSTs. Furthermore, reversible transformations between different shapes of PS‐b‐P4VP particles are successfully demonstrated using a solvent‐adsorption annealing with chloroform, suggesting great promise of these particles for sensing, smart coating, and drug delivery applications.     

Templated synthesis of Ag loaded TiO2 nanostructures using amphiphilic polyelectrolyte

A graft-type amphiphilic polyelectrolyte, i.e. poly(vinylidene fluoride-co-chlorotrifluoroethylene)-g-poly(styrene sulfonic acid) (P(VDF-co-CTFE)-g-PSSA) with 47 wt.% of PSSA was synthesized via atom transfer radical polymerization (ATRP) and used as a template film for the in-situ formation of Ag nanoparticles. This nanocomposite material was further combined with titanium(IV) isopropoxide (TTIP) to form Ag loaded TiO₂ nanostructural hybrid materials. UV-visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed successful synthesis of Ag-TiO₂ nanostructures templated in the P(VDF-co-CTFE)-g-PSSA graft copolymer film. It was also found that the d-spacing of the graft copolymer in XRD patterns was increased from 4.1 to 4.4 Å, presumably due to the chain expansion resulting from the incorporation of nanoparticles in highly entangled polymeric chains.     

Fabrication and characterization of thermoresponsive Fe3O4@PNIPAM hybrid nanomaterials by surface-initiated RAFT polymerization

A versatile route applied to the synthesis of thermoresponsive magnetite nanoparticles involved the formation of nanoparticles by coprecipitation of Fe²⁺/Fe³⁺ in the presence of an alkaline solution, followed by attachment of the reversible addition-fragmentation transfer (RAFT) agents onto the surface of the Fe₃O₄ nanoparticles via the electrostatic interactions, subsequent grafting from polymerization of N-isopropylacrylamide (NIPAM) through surface-initiated RAFT polymerization. The surface-initiated RAFT polymerization can be conducted in a well-controlled manner, as revealed by the linear kinetic plot, linear evolution of number-average molecular weights (M _n ) versus monomer conversions, and the relatively narrow molecular weight distributions (M _w /M _n ?相似文献   

Synthesis, characterization and fluorescence property of CdS/P(N-iPAAm) nanocomposites

A novel nanocomposite in which CdS nanoparticles were embedded in poly(N-isopropylacrylamide) (P(N-iPAAm)) matrix have been fabricated. The particle size of CdS nanoparticles ranged from 10 nm to 40 nm could be adjusted with the varying of the inorganic contents. The nanocomposites have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), high resolution transmission electron microscope (HRTEM), UV-vis absorption and fluorescence spectra (FLS) measurements. The cell volume of CdS nanoparticles embedded in polymer matrix was smaller than the standard value and the nanocomposites with 12.0% inorganic content showed a good fluorescence property.     

Cell attachment/detachment behavior on poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide)-based microgel films: the effect of microgel structure and swelling ratio

Microgels are cross-linked soft particles with a three-dimensional network structure that are swollen in a good solvent. Poly(N-isopropylacrylamide) (pNIPAAm)-based microgels have attracted great attentions for their temperature responsive property, particularly in recent years, pNIPAAm-based microgel films were utilized as a new kind of thermoresponsive surface to tune cell attachment/detachment behavior via temperature stimuli. However, some results are not consistent, for example, different polymerization conditions may bring out different results even for pure pNIPAAm microgel. This work aims to find out which factor plays the critical role for successful cell detachment on the pNIPAAm-based microgel films. The results unraveled that the structure and swelling ratio of the microgel rather than the film thickness plays a key role on the successful cells detachment, unlike linear pNIPAAm films in which the cells’ attach/detach property is only determined by the film thickness. For poly(N-isopropylacrylamide–styrene) microgel film, NIH3T3 cells could only detach when the microgel has a uniform structure and the volume dilatation of the microgel (20/38 °C) is larger than 4.     

All-conjugated amphiphilic diblock copolymers for improving morphology and thermal stability of polymer/nanocrystals hybrid solar cells

Herein, the ability to optimize the morphology and photovoltaic performance of poly(3-hexylthiophene) (P3HT)/ZnO hybrid bulk-heterojunction solar cells via introducing all-conjugated amphiphilic P3HT-based block copolymer (BCP), poly(3-hexylthiophene)-block-poly(3-triethylene glycol-thiophene) (P3HT-b-P3TEGT), as polymeric additives is demonstrated. The results show that the addition of P3HT-b-P3TEGT additives can effectively improve the compatibility between P3HT and ZnO nanocrystals, increase the crystalline and ordered packing of P3HT chains, and form optimized hybrid nanomorphology with stable and intimate hybrid interface. The improvement is ascribed to the P3HT-b-P3TEGT at the P3HT/ZnO interface that has strong coordination interactions between the TEG side chains and the polar surface of ZnO nanoparticles. All of these are favor of the efficient exciton dissociation, charge separation and transport, thereby, contributing to the improvement of the efficiency and thermal stability of solar cells. These observations indicate that introducing all-conjugated amphiphilic BCP additives can be a promising and effective protocol for high-performance hybrid solar cells.     

Engineering of poly(ethylene glycol) chain-tethered surfaces to obtain high-performance bionanoparticles

Abstract

A poly(ethylene glycol)-b-poly[2-(N,N-dimethylamino)ethyl methacrylate] block copolymer possessing a reactive acetal group at the end of the poly(ethylene glycol) (PEG) chain, that is, acetal-PEG-b-PAMA, was synthesized by a proprietary polymerization technique. Gold nanoparticles (GNPs) were prepared using the thus-synthesized acetal-PEG-b-PAMA block copolymer. The PEG-b-PAMA not only acted as a reducing agent of aurate ions but also attached to the nanoparticle surface. The GNPs obtained had controlled sizes and narrow size distributions. They also showed high dispersion stability owing to the presence of PEG tethering chains on the surface. The same strategy should also be applicable to the fabrication of semiconductor quantum dots and inorganic porous nanoparticles. The preparation of nanoparticles in situ, i.e. in the presence of acetal-PEG-b-PAMA, gave the most densely packed polymer layer on the nanoparticle surface; this was not observed when coating preformed nanoparticles. PEG/polyamine block copolymer was more functional on the metal surface than PEG/polyamine graft copolymer, as confirmed by angle-dependent x-ray photoelectron spectroscopy. We successfully solubilized the C₆₀ fullerene into aqueous media using acetal-PEG-b-PAMA. A C₆₀/acetal-PEG-b-PAMA complex with a size below 5 nm was obtained by dialysis. The preparation and characterization of these materials are described in this review.