Poly(ethylene oxide)–poly(ethylene imine) block copolymers as templates and catalysts for the in situ formation of monodisperse silica nanospheres

Block copolymers based on poly(ethylene oxide) (PEO) and poly(ethylene imine) (PEI) are efficient catalysts/templates for the formation of uniform silica nanoparticles. Addition of tetraethylorthosilicate to a solution of PEO–PEI or PEI–PEO–PEI block copolymers results in the formation of silica particles with a diameter of ca. 30 nm and narrow size distribution. The particles precipitated with the diblock copolymers can be redispersed in water after isolation as individual nanoparticles. Evidently, block copolymers based on PEO and PEI serve as excellent templates for the biomimetic and “soft” synthesis of silica nanoparticles.

Crosslinked QA‐PEI nanoparticles: synthesis reproducibility,chemical modifications,and stability study

Quaternary ammonium polyethylenimine (QA‐PEI) nanoparticles were synthesized by PEI crosslinking and alkylation with octyliodide followed by quaternization by methyl iodide. The present study focuses on the reproducibility of particles formation with respect to particle size, positive charge, oxidative, thermal stability and antibacterial activity. The QA‐PEI‐based nanoparticles with particle size in the range of 160–190 nm were synthesized in high reproducibility and showed high chemical stability against environmental changes including exposure to different oxidizers and storage conditions. QA‐PEI nanoparticles incorporated in dental restorative resin composites at 2% w/w demonstrated strong antibacterial activity. Copyright © 2013 John Wiley & Sons, Ltd.     

Maghemite nanoparticles protectively coated with poly(ethylene imine) and poly(ethylene oxide)-block-poly(glutamic acid)

Superparamagnetic iron oxide particles (SPIO) of maghemite were prepared in aqueous solution and subsequently stabilized with polymers in two layer-by-layer deposition steps. The first layer around the maghemite core is formed by poly(ethylene imine) (PEI), and the second one is formed by poly(ethylene oxide)-block-poly(glutamic acid) (PEO-PGA). The hydrodynamic diameter of the particles increases stepwise from D(h) = 25 nm (parent) via 35 nm (PEI) to 46 nm (PEI plus PEO-PGA) due to stabilization. This is accompanied by a switching of their zeta-potentials from moderately positive (+28 mV) to highly positive (+50 mV) and finally slightly negative (-3 mV). By contrast, the polydispersity indexes of the particles remain constant (ca. 0.15). M?ssbauer spectroscopy revealed that the iron oxide, which forms the core of the particles, is only present as Fe(III) in the form of superparamagnetic maghemite nanocrystals. The magnetic domains and the maghemite crystallites were found to be identical with a size of 12.0 +/- 0.5 nm. The coated maghemite nanoparticles were tested to be stable in water and in physiological salt solution for longer than 6 months. In contrast to novel methods for magnetic nanoparticle production, where organic solvents are necessary, the procedure proposed here can dispense with organic solvents. Magnetic resonance imaging (MRI) experiments on living rats indicate that the nanoparticles are useful as an MRI contrast agent.     

Antibacterial poly(ethylene glycol) hydrogels from combined epoxy‐amine and thiol‐ene click reaction

Antibacterial hydrogels containing quaternary ammonium (QA) groups were prepared via a facile thiol‐ene “click” reaction using multifunctional poly(ethylene glycol) (PEG). The multifunctional PEG polymers were prepared by an epoxy‐amine ring opening reaction. The chemical and physical properties of the hydrogels could be tuned with different crosslinking structures and crosslinking densities. The antibacterial hydrogel structures prepared from PEG Pendant QA were less well‐defined than those from PEG Chain‐End QA. Furthermore, functionalization of the PEG‐type hydrogels with QA groups produced strong antibacterial abilities against Staphylococcus aureus, and therefore has the potential to be used as an anti‐infective material for biomedical devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 656–667     

Poly(ethylene imine)‐graft‐poly(ethylene oxide) brush‐like copolymers: Preparation,thermal properties,and selective supramolecular inclusion complexation with α‐cyclodextrin

Poly(ethylene imine)‐graft‐poly(ethylene oxide) (PEI‐g‐PEO) copolymers were synthesized via Michael addition reaction between acryl‐terminated poly(ethylene oxide) methyl ether (PEO) and poly(ethylene imine) (PEI). The brush‐like copolymers were characterized by means of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. It is found that the crystallinity of the PEO side chains in the copolymers remained unaffected by the PEI backbone whereas the crystal structure of PEO side chains was altered to some extent by the PEI backbone. The crystallization behavior of PEO blocks in the copolymers suggests that the bush‐shaped copolymers are microphase‐separated in the molten state. The PEO side chains of the copolymers were selectively complexed with α‐cyclodextrin (α‐CD) to afford hydrophobic side chains (i.e., PEO/α‐CD inclusion complexes). The X‐ray diffraction (XRD) shows that the inclusion complexes (ICs) of the PEO side chains displayed a channel‐type crystalline structure. It is identified that the stoichiometry of the inclusion complexation of the PEI‐g‐PEO with α‐CD is close to that of the control PEO with α‐CD. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2296–2306, 2008     

Self‐Assembly of Rod–Coil Polyethylenimine–Poly(ethylene glycol)–α‐Cyclodextrin Inclusion Complexes into Hollow Spheres and Rod‐Like Particles

This paper describes the self‐assembly of rod–coil inclusion complexes, polyethylenimine–poly(ethylene glycol)–α‐cyclodextrin (PEI–PEG–α‐CD). It is demonstrated that α‐CDs should exclusively thread on the PEG block in PEI–PEG copolymers and the resulting complexes have both rigid block (PEG–α‐CD) and coil block (protonated PEI). By varying the rigid block fraction, aggregates with hollow spheres or rod‐like particles could be formed simply by self‐assembly in aqueous solution.     

Microstructured reaction areas for the deposition of silica

Patterned films with hexagonal structures were prepared by photochemical grafting of hydrophobic poly(acrylic acid 2-ethyl-hexylester) (PEHAA) as barrier and poly(ethylene imine) (PEI) as reaction area. The films have been characterized by ellipsometry, contact angle measurements, and scanning electron microscopy (SEM). These patterned films have been used in silica mineralization experiments by dipping them into a silica precursor solution. Silica deposition occurs only in PEI-coated areas, resulting in regular arrays of lens-shaped silica particles. The deposited silica was investigated by SEM and atomic force microscopy (AFM). Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Preparation and properties of ionic‐liquid‐containing poly(ethylene glycol)‐based networked polymer films having lithium salt structures

Ionic‐liquid‐containing polymer films were prepared by swelling poly(ethylene glycol)‐based networked polymers having lithium salt structures with an ionic liquid, 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EMImFSI), or with an EMImFSI solution of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). Their fundamental physical properties were investigated. The networked polymer films having lithium salt structures were prepared by curing a mixture of poly(ethylene glycol) diglycidyl ether and lithium 3‐glycidyloxypropanesulfonate or lithium 3‐(glycidyloxypropanesulfonyl)(trifluoromethanesulfonyl)imide with poly(ethylene glycol) bis(3‐aminopropyl) terminated. The obtained ionic‐liquid‐containing films were flexible and self‐standing. They showed high ionic conductivity at room temperature, 1.16–2.09 S/m for samples without LiTFSI and 0.29–0.43 S/m for those with 10 wt % LiTFSI. Their thermal decomposition temperature was above 220 °C, and melting temperature of the ionic liquid incorporated in the film was around ?16 °C. They exhibited high safety due to good nonflammability of the ionic liquid. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A novel solventless coating method to graft low‐molecular weight polyethyleneimine on silica fine powders

The overall objective of the present study was to modulate the surface characteristics of aerogel‐like submicron and nanometric particles by coating them with polyethyleneimine (PEI) to suit specific biological applications. A new process for the covalent grafting of low‐molecular weight PEI chains has been described, based on the use of compressed CO₂ as the initiator of the ring opening polymerization of the ethyleneimine monomer, which was performed in the presence of silica particles. Coating was done at low pressure and temperature and in the absence of any organic solvent. Obtained materials were compared with a product prepared following the standard soaking procedure for PEI coating. Materials were characterized regarding composition, structure, surface charge, particle size, morphology, and drug release. The developed process led to the covalent grafting of low‐molecular weight PEI on the silica surface, which conferred an increased thermal stability for the coating and low cytotoxicity to the particles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2760–2768     

Silica‐particle‐supported zwitterionic polymer monolith for microcolumn liquid chromatography

A silica‐particle‐supported zwitterionic polymeric monolithic column, shortened as supported column (S‐column), was prepared by the in situ polymerization of methacrylic acid, ethylene dimethacrylate, and 2‐(dimethylamino)ethyl methacrylate in the presence of a ternary porogenic solvent containing water, methanol, and cyclohexanol in a 250 μm id fused‐silica capillary prepacked with 5 μm bare silica particles. In the S‐column, a thin layer of the polymers was formed around the silica particles in the form of nanoglobules, leaving the interstitial spaces between the particles free for liquid flow. The effects of the preparation conditions on the morphology of the monolith were investigated by scanning electron microscopy and backpressure measurements. The selected volumetric ratio of porogens, monomer concentration, polymerization time, and temperature are 1:1:8 (water/methanol/cyclohexanol), 25% v/v, 5 h, and 60°C, respectively. The S‐column was evaluated by comparison with its conventional organic counterpart in terms of morphology, mechanical stability, permeability, swelling–shrinking behavior, capacity, and efficiency. The results demonstrate that the S‐column is superior to its counterpart in all the terms with the exception of permeability. The above merits and zwitterionic property of the S‐column were further confirmed by separate separations of four inorganic anions and three organic cations.     

Synthesis and gas barrier characterization of poly(ethylene isophthalate)

Poly(ethylene isophthalate) (PEI) was synthesized for this research with essentially a condensation polymerization of isophthalic acid and ethylene glycol catalyzed by zinc acetate and antimony trioxide. Several samples were obtained, and their characteristics were observed and compared with poly(ethylene terephthalate) (PET). The synthesized PEI samples were chemically identified by ¹H NMR. Thermal analysis with differential scanning calorimetry (DSC) yielded results that indicate the samples were primarily amorphous, with a glass‐transition temperature of 55–60 °C. Molecular weights of these PEI samples were also obtained through intrinsic viscosity measurements (Mark–Houwink equation). Molecular weights varied with conditions of the polymerization, and the highest molecular weight achieved was 21,000 g/mol. Finally, the diffusion coefficient, solubility, and permeability of CO₂ gas in PEI were measured and found to be substantially lower than in PET, as anticipated from their isomeric chemical structures. This is because in PET the phenyl rings are substituted in the para (1,4) positions, which allows for their facile flipping, effectively permitting gases to pass through. However, the meta‐substituted phenyl rings in PEI do not permit such ring flipping, and thus PEI may be more suitable for barrier applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4247–4254, 2004     

Strategies toward biocompatible artificial implants: Grafting of functionalized poly(ethylene glycol)s to poly(ethylene terephthalate) surfaces

Epoxide and aldehyde end‐functionalized poly(ethylene glycol)s (PEGs) (M_w = 400, 1000, 3400, 5000, and 20,000) were grafted to poly(ethylene terephthalate) (PET) film substrates that contained amine or alcohol groups. PET‐PAH and PET‐PEI were prepared by reacting poly(allylamine) (PAH) and polyethylenimine (PEI) with PET substrates, respectively; PET‐PVOH was prepared by the adsorption of poly(vinyl alcohol) (PVOH) to PET substrates. Grafting was characterized and quantified by the increase of the intensity of the PEG carbon peak in the X‐ray photoelectron spectra. Grafting yield was optimized by controlling reaction parameters and was found to be substrate‐independent in general. Graft density consistently decreased as PEG chain length was increased. This is likely due to the higher steric requirement of higher molecular weight PEG molecules. Water contact angles of surfaces containing long PEG chains (3400, 5000, and 20,000) are much lower than those containing shorter PEG chains (400 and 1000). This indicates that longer PEG chains are more effective in rendering surfaces hydrophilic. Protein adsorption experiments were carried out on PET‐ and PEG‐modified derivatives using collagen, lysozyme, and albumin. After PEG grafting, the amount of protein adsorbed was reduced in all cases. Trends in surface requirements for protein resistance are: surfaces with longer PEG chains and higher chain density, especially the former, are more protein resistant; PEG grafted to surfaces containing branched or network polymers is not effective at covering the underlying substrate, and thus does not protect the entire surface from protein adsorption; and substrates containing surface charge are less protein‐resistant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5389–5400, 2004     

Direct force measurement of the stability of poly(ethylene glycol)-polyethylenimine graft films

The stability and passivity of poly(ethylene glycol)-polyethylenimine (PEG-PEI) graft films are important for their use as antifouling coatings in a variety of biotechnology applications. We have used AFM colloidal-probe force measurements combined with optical reflectometry to characterize the surface properties and stability of PEI and dense PEG-PEI graft films on silica. Initial contact between bare silica probes and PEI-modified surfaces yields force curves that exhibit a long-range electrostatic repulsion and short-range attraction between the surfaces, indicating spontaneous desorption of PEI in the aqueous medium. Further transfer of PEI molecules to the probe occurs with subsequent application of forces between FR = 300 and 500 microN/m. The presence of PEG reduces the adhesive properties of the PEI surface and prevents transfer of PEI molecules to the probe with continuous contact, though an initial desorption of PEI still occurs. Glutaraldehyde crosslinking of the graft films prevents both the initial desorption and subsequent transfer of the PEI, resulting in sustained attractive interaction forces of electrostatic origin between the negatively charged probe and the positively charged copolymer graft films.     

Adsorption of polyelectrolyte modified graphene to silica surfaces: monolayers and multilayers

Exfoliated graphene particles stabilised by the cationic polyelectrolyte polyethyleneimine (PEI) were used in conjunction with an anionic polyelectrolyte, poly(acrylic acid), to construct multilayers using the layer-by-layer technique on a silica substrate. In the first adsorption step, the surface excess of the cationic graphene was dependent on the overall charge on the nanoparticle which in turn can be tuned through modifying solution pH as PEI has weakly ionisable charged amine groups. The adsorbed amount onto the silica surface increased as the solution pH increased. Subsequently, a layer of PAA was adsorbed on top of the cationic graphene through electrostatic interaction. The multilayer could be assembled through this alternate deposition, with the influence of solution conditions investigated. The pH of the adsorbing solutions was the chief determinant of the overall adsorbed amounts, with more mass added at the elevated pH of 9 in comparison with pH 4. Atomic force microscopy confirmed that the graphene particles were adsorbed to the silica interface and that the surface coverage of the disc-like nanoparticles was complete after the deposition of five graphene-polyelectrolyte bi-layers. Furthermore, the graphene nanoparticles themselves could be modified through the consecutive addition of the oppositely charged polymers. A multilayered assembly of negatively charged graphene sheets modified with a bi-layer of PEI and PAA was also deposited on a silica surface with adsorbed PEI.     

C<Subscript>18</Subscript>-Free Organic–Inorganic Hybrid Silica Particles Derived from Sole Silsesquioxane for Reversed-Phase HPLC

Ethyl-bridged organic–inorganic hybrid silica particles were prepared via a sol–gel and hydrothermal synthesis approach using 1,2-bis(triethoxysilyl)ethane (BTESE) as the sole precursor, and triblock copolymer poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (P123) and dodecyltrimethylammonium bromide (DTAB) as combined templates. The morphology, pore structure, chemical composition and liquid chromatographic performance of the obtained materials were investigated in detail. The particles exhibit a high surface area of 1136.40 m²/g, together with a pore volume of 0.39 cm³/g and an average pore size of 2.30 nm. Used as stationary phase for high-performance liquid chromatography (HPLC), the particles without extra bonding either C₁₈ or C₈ can successfully separate a mixture of uracil, phenol, pyridine, methylbenzene, ethylbenzene and tert-butylbenzene. The obtained materials also show practical application in the separation of phthalate acid esters (PAEs), which are harmful to environment and human health. Although the columns packed with ethyl-bridged organic–inorganic hybrid silica show lower column efficiency and peak symmetry compared to commercial column, they have considerably higher chemical stability in alkaline mobile phase. The HSS column also possesses high mechanical stability which is similar to that of the commercial column.     

Enzyme-modified nanoparticles using biomimetically synthesized silica

The entrapment of enzymes within biomimetic silica nanoparticles offers unique and simple immobilization protocols that merge the stability of proteins confined in solid phases with the high loading and reduced diffusion limitations inherent to nano-sized structures. Herein, we report on the biomimetic silica entrapment of chemically derivatized horseradish peroxidase for amperometric sensing applications. Scanning electron microscopy shows evidence of the formation of enzyme-modified nanospheres using poly(ethylenimine) as a template for silicic acid condensation. When these nanospheres are directly deposited on graphite electrodes, chemically modified anionic peroxidase shows direct electron transfer at 0 mV vs Ag|AgCl. Microgravimetric measurements as well as SEM images demonstrate that negatively charged peroxidase is also entrapped when silica precipitates at gold electrodes are modified with a self-assembled monolayer of poly(ethylenimine). Electrostatic interactions may play a crucial role for efficient enzyme entrapment and silica condensation at the PEI template monolayer. The in-situ biomimetically synthesized peroxidase nanospheres are catalytically active, enabling direct bioelectrocatalysis at 0 mV vs Ag|AgCl with long-term stability.     

Target‐Specific Capture of Environmentally Relevant Gaseous Aldehydes and Carboxylic Acids with Functional Nanoparticles

Aldehyde and carboxylic acid volatile organic compounds (VOCs) present significant environmental concern due to their prevalence in the atmosphere. We developed biodegradable functional nanoparticles comprised of poly(d,l ‐lactic acid)‐poly(ethylene glycol)‐poly(ethyleneimine) (PDLLA‐PEG‐PEI) block co‐polymers that capture these VOCs by chemical reaction. Polymeric nanoparticles (NPs) preparation involved nanoprecipitation and surface functionalization with branched PEI. The PDLLA‐PEG‐PEI NPs were characterized by using TGA, IR, ¹H NMR, elemental analysis, and TEM. The materials feature 1°, 2°, and 3° amines on their surface, capable of capturing aldehydes and carboxylic acids from gaseous mixtures. Aldehydes were captured by a condensation reaction forming imines, whereas carboxylic acids were captured by acid/base reaction. These materials reacted selectively with target contaminants obviating off‐target binding when challenged by other VOCs with orthogonal reactivity. The NPs outperformed conventional activated carbon sorbents.     

Elaboration of fluorescent and highly magnetic submicronic polymer particles via a stepwise heterocoagulation process

Using the stepwise heterocoagulation concept, fluorescent and highly magnetic submicronic core-shell polymer particles were prepared. For this purpose a negatively charged oil-in-water magnetic emulsion was first modified by adsorbing the poly(ethyleneimine) (PEI). Secondly, low glass transition temperature (T _g=10°C) anionic film-forming nanoparticles were adsorbed onto the cationic magnetic droplets. Finally the encapsulation was induced by heating the heterocoagulates above the T _g of the film-forming nanoparticles. To produce labeled magnetic particles, fluorescent nanoparticles and film-forming nanoparticles were simultaneously adsorbed. PEI adsorption was investigated. Also investigated was the influence of the amount of film-forming nanoparticles and fluorescent nanoparticles on the encapsulation efficiency.     

Telechelic,Antimicrobial Hydrophilic Polycations with Two Modes of Action

Telechelic antimicrobial poly(2‐oxazoline)s with quaternary ammonium (quat) end groups are shown to be potent antimicrobial polymers against Gram‐positive bacterial strains. In this study, the activity against the Gram‐negative bacterium Escherichia coli is additionally implemented by hydrolyzing the poly(2‐methyl‐2‐oxazoline) with two quart end groups to poly(ethylene imine) (PEI). The resulting telechelic polycations are active against Staphylococcus aureus and E. coli. The contribution of the PEI backbone is determined by measuring the antimicrobial activity in the presence of calcium ions. The influence of PEI on the overall activity strongly depends on the molecular weight and increases with higher mass. The PEI dominates the activity against E. coli at lower masses than against S. aureus. The quart end groups require an alkyl substituent of dodecyl or longer to dominate the antimicrobial activity. Additionally, PEI and quart end groups act synergistically.     

Synthesis of poly(ethylene glycol)/polypeptide/poly(D,L‐lactide) copolymers and their nanoparticles

Core‐shell structured nanoparticles of poly(ethylene glycol) (PEG)/polypeptide/poly(D ,L ‐lactide) (PLA) copolymers were prepared and their properties were investigated. The copolymers had a poly(L ‐serine) or poly(L ‐phenylalanine) block as a linker between a hydrophilic PEG and a hydrophobic PLA unit. They formed core‐shell structured nanoparticles, where the polypeptide block resided at the interface between a hydrophilic PEG shell and a hydrophobic PLA core. In the synthesis, poly(ethylene glycol)‐b‐poly(L ‐serine) (PEG‐PSER) was prepared by ring opening polymerization of N‐carboxyanhydride of O‐(tert‐butyl)‐L ‐serine and subsequent removal of tert‐butyl groups. Poly(ethylene glycol)‐b‐poly(L ‐phenylalanine) (PEG‐PPA) was obtained by ring opening polymerization of N‐carboxyanhydride of L ‐phenylalanine. Methoxy‐poly(ethylene glycol)‐amine with a MW of 5000 was used as an initiator for both polymerizations. The polymerization of D ,L ‐lactide by initiation with PEG‐PSER and PEG‐PPA produced a comb‐like copolymer, poly(ethylene glycol)‐b‐[poly(L ‐serine)‐g‐poly(D ,L ‐lactide)] (PEG‐PSER‐PLA) and a linear copolymer, poly(ethylene glycol)‐b‐poly(L ‐phenylalanine)‐b‐poly(D ,L ‐lactide) (PEG‐PPA‐PLA), respectively. The nanoparticles obtained from PEG‐PPA‐PLA showed a negative zeta potential value of ?16.6 mV, while those of PEG‐PSER‐PLA exhibited a positive value of about 19.3 mV. In pH 7.0 phosphate buffer solution at 36 °C, the nanoparticles of PEG/polypeptide/PLA copolymers showed much better stability than those of a linear PEG‐PLA copolymer having a comparable molecular weight. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011