Intraparticle Crosslinking Research Articles

Highly Controllable Nanoassemblies of Luminescent Gold Nanoparticles with Abnormal Disassembly‐Induced Emission Enhancement for In Vivo Imaging Applications

AbstractAssembly‐induced emission enhancement has been widely observed for luminophors but it causes emission decrease after disassembly. The construction of unique nanoassemblies with disassembly‐induced emission enhancement (DIEE) is demanded. Herein, by taking advantages of alterable siloxane bridge crosslinking states, we report a facile strategy to fabricate water‐soluble nanoassemblies of luminescent gold nanoparticles (AuNPs) with abnormal DIEE. The fabricated AuNP nanoassemblies with dominant interparticle crosslinking showed a redshifted emission at ≈1070 nm with quantum yields (QYs) of 1.8 %. After disassembly, the nanoassemblies with increased intraparticle crosslinking exhibited a unique DIEE (>6 folds, QYs, 12 %) due to the enhanced ligand‐to‐metal charge transition. Besides, the disassembly facilitated renal clearance of AuNPs to reduce nonspecific retention in the body, opening new possibilities for designing highly emissive renal‐clearable nanostructures toward more bioapplications.

Synthesis of Cross-Linked Block Copolymer Nanoassemblies and their Coating Application.

Since the discovery of polymerization-induced self-assembly (PISA), convenient synthesis of concentrated block copolymer nanoassemblies dispersed in solvent has been achieved. Now, application of block copolymer nanoassemblies should be paid more attention. In this study, corona-cross-linked block copolymer nanoparticles of poly[dimethylacrylamide-co-(diacetone acrylamide)]-b-polystyrene [P(DMA-co-DAAM)-b-PS] containing the poly(DAAM) segment in the hydrophilic P(DMA-co-DAAM) block are synthesized initially by PISA following dispersion reversible addition-fragmentation chain transfer polymerization and then by covalent intraparticle cross-linking through the poly(DAAM) segment and adipic acid dihydrazide. Coating application of the corona-cross-linked block copolymer nanoassemblies is tried, and much higher water resistance of the corona-cross-linked block copolymer nanoassemblies than that of the linear block copolymer nanoassemblies is demonstrated.

Influence of intraparticle cross-linking on polymer diffusion in latex films prepared from secondary dispersions

In this work, we synthesized surfactant-free latex dispersions of nanoparticles (NPs) based upon emulsification of a preformed proprietary BASF polymer (MnGPC = 5000 g/mol, Ð = 3, denoted as Pol), in which the —COOH groups were partially neutralized by ammonia. To obtain useful coatings with polymers of such low molecular weight (MW), we approached this problem through the reaction of carboxylated polymer dispersions with neopentyl glycol diglycidyl ether (NGDE, 20 to 60 mol% based on carboxyl groups) to increase the MW and to introduce gel content. We employed AFM to monitor the influence of cross-link density on the surface roughness and found the presence of cross-links increases the resistance of particles to deformation. Fluorescence resonance energy transfer (FRET) measurements were carried out to determine the extent of polymer mixing upon film formation. Our most important finding is that the gel content substantially limited the extent of molecular mixing at long annealing times or in corresponding solvent-cast films. In parallel, we carried out a series of similar reactions on the secondary dispersion particles with a monoepoxide, consisting of a mixture of dodecyl and tetradecyl glycidyl ether. This reaction maintained the size and size distribution of the latex particles. These polymers had no gel content, but the reaction with the epoxide lowered the Tg of the polymer. FRET studies showed a pronounced influence of Tg on the rates of polymer diffusion in these films.

Rational Design of Surface-State Controlled Multicolor Cross-Linked Carbon Dots with Distinct Photoluminescence and Cellular Uptake Properties.

We disclose for the first time a facile synthetic methodology for the preparation of multicolor carbon dots (CDs) from a single source barring any chromatographic separations. This was achieved via sequential intraparticle cross-linking of surface abundant carboxylic acid groups on the CDs synthesized from a precursor to control their photoluminescence (PL) spectra as well as affect their degree of cellular internalization in cancer cells. The change in PL spectra with sequential cross-linking was projected by theoretical density functional theory (DFT) studies and validated by multiple characterization tools such as X-ray photoelectron spectroscopy (XPS), PL spectroscopy, ninhydrin assay, etc. The variation in cellular internalization of these cross-linked CDs was demonstrated using inhibitor assays, confocal microscopy, and flow cytometry. We supplemented our findings with high-resolution dark-field imaging to visualize and confirm the colocalization of these CDs into distinct intracellular compartments. Finally, to prove the surface-state controlled PL mechanisms of these cross-linked CDs, we fabricated a triple-channel sensor array for the identification of different analytes including metal ions and biologically relevant proteins.

Interparticle cycloaddition reactions for morphology transition of coumarin-functionalized stimuli-responsive polymer nanoparticles prepared by surfactant-free dispersion polymerization

Stimuli-responsive polymer nanoparticles were synthesized by surfactant-free dispersion polymerization of styrene and 2-(dimethylamino)ethyl methacrylate (DMAEMA) in three different contents of divinylbenzene intraparticle crosslinking agent. Incorporation of the hydrophilic DMAEMA comonomer during the polymerization yielded pH-responsive nanogels with a higher size than the polystyrene nanoparticles. Surface of the nanoparticles was decorated with 7-hydroxyl-4-methylcoumarin (HMC) via an esterification reaction to yield stimuli-responsive fluorescent nanogels. The monodispersed polymer nanoparticles with spherical morphology were turned into chain-like coupled structures because of interparticle cycloaddition reactions between the surface HMC moieties upon UV irradiation, as shown by scanning and transmission electron microscopies. Dimerization of the HMC-functionalized nanoparticles was investigated by ultraviolet–visible spectrophotometer and fluorescence spectroscopy. Size and its distribution for the nanoparticles before and after light irradiation were determined using dynamic light scattering. From a different view, decreasing the intraparticle crosslinking density and also purging the colloidal dispersions with CO2 were resulted in a higher mean particle size. Variation of particle size by purging CO2 and consequently at different pH values was resulted in different fluorescence characteristics. Therefore, these stimuli-responsive fluorescent nanoparticles were finally used as a pH indicator in the presence of CO2 gas or even at different pH values using fluorescence spectroscopy.

Solvent-Resistant Lignin-Epoxy Hybrid Nanoparticles for Covalent Surface Modification and High-Strength Particulate Adhesives.

Fabrication of spherical lignin nanoparticles (LNPs) is opening more application opportunities for lignin. However, dissolution of LNPs at a strongly alkaline pH or in common organic solvent systems has prevented their surface functionalization in a dispersion state as well as processing and applications that require maintaining the particle morphology under harsh conditions. Here, we report a simple method to stabilize LNPs through intraparticle cross-linking. Bisphenol A diglycidyl ether (BADGE), a cross-linker that, like lignin, contains substituted benzene rings, is coprecipitated with softwood Kraft lignin to form hybrid LNPs (hy-LNPs). The hy-LNPs with a BADGE content ≤20 wt % could be intraparticle cross-linked in the dispersion state without altering their colloidal stability. Atomic force microscopy and quartz crystal microbalance with dissipation monitoring were used to show that the internally cross-linked particles were resistant to dissolution under strongly alkaline conditions and in acetone-water binary solvent that dissolved unmodified LNPs entirely. We further demonstrated covalent surface functionalization of the internally cross-linked particles at pH 12 through an epoxy ring-opening reaction to obtain particles with pH-switchable surface charge. Moreover, the hy-LNPs with BADGE content ≥30% allowed both inter- and intraparticle cross-linking at >150 °C, which enabled their application as waterborne wood adhesives with competitive dry/wet adhesive strength (5.4/3.5 MPa).

Adhesive Reactive Nanoparticles of Poly(ethyleneimine)/Poly(maleic acid-co -propylene) Complexes: A Novel Concept for the Immobilization of Pollutant Removing Laccase

Nanoparticles (NPs) based on the complexation of anionic poly(maleic acid-co-propylene) (PMAP) and cationic poly(ethyleneimine) (PEI) are introduced as novel strategy to immobilize pollutant removing enzymes under mild, aqueous, and nontoxic conditions, in few processing steps. PEI/PMAP NP size 80–230 nm and are colloidally stable. Dried PEI/PMAP NP at model substrates remain bound after water contact if molar mixing ratio between cationic and anionic groups is close to unity. This study claims deswelling by drying, hydrophobic nature, and merging of PEI/PMAP NP as prime factors for adhesive stability. Furthermore PEI/PMAP NPs bear uncomplexed free maleic acid groups of PMAP, which react to maleic anhydride groups above 100 °C. These maleic anhydride groups can be used for both additional intraparticle crosslinking of PEI/PMAP NP and intermolecular linkage of enzymes under formation of imide or amide chemical bonds. Herein, laccase is either bound to precasted binary PEI/PMAP NP films or integrated into casted ternary laccase/PEI/PMAP NP films. Bound or integrated laccase shows significant enzymatic activity toward model pollutant guaiacol. Laccase bound by electrostatic attraction shows slightly higher enzymatic activity compared to chemical linkage at PEI/PMAP NP films. After five consecutive cycles of guaiacol conversion above laccase/PEI/PMAP NP film activity remains dropping to 30% of initial value.

Ca2+ Responsive Microgel-Stabilized Pickering Emulsions

As an ionic cross-linker that can change the size of poly(N-isopropylacrylamide-co-acrylic acid) microgel, Ca2+ is applied as a trigger to demulsify microgel-stabilized oil/water Pickering emulsions. The influence of Ca2+ induced intra-particle ionic cross-linking and inter-particle aggregation on the stability of microgel-stablized “Pickering” emulsion is described. At low and mediate concentration of Ca2+, ionic cross-linking can change the internal elasticity of the microgel, and cause the coarsening of the oil droplets. At high concentration of Ca2+, microgels flocculate due to the salt out effect and the emulsion is destabilized. This work provide a facile method to control the stability of the Pickering emulsions at ambient condition.

Study of the film formation and mechanical properties of the latexes obtained by miniemulsion co-polymerization of butyl acrylate, methyl acrylate and 3-methacryloxypropyltrimethoxysilane

Miniemulsion polymerization offers several advantages over conventional emulsion polymerization to co-polymerize alkoxysilane monomers, which easily undergo premature hydrolysis and condensation reaction into the polymer particles. The premature hydrolysis and the subsequent condensation reaction can lead to colloidal instability. Furthermore, the premature intra-particle cross-linking will reduce the capability of the latex particles to form films. In this paper we discuss the miniemulsion co-polymerization of the butyl acrylate, methyl acrylate and 3-methacryloxypropyltrimethoxysilane BA–MA–MEMO. The latexes features have been characterized and a compressive explanation of the features has been given. Finally, the work focussed on the study of the latex film formation, and mechanical properties by using nanoindentation trials to measure the superficial properties of the film, and also stress–strain curves have been produced.

Tuning the swelling and mechanical properties of pH-responsive doubly crosslinked microgels using particle composition

pH-Responsive microgel particles are crosslinked polymer colloid particles that swell when the pH approaches the pKa. They have attracted a great deal of interest because of the ability to prepare stimulus responsive dispersions. Microgels that have only one form of crosslinking are termed singly crosslinked microgels (SX microgels). SX microgels are defined here as microgel particles that contain intra-particle linkages as the only source of covalent crosslinks. Recently, we introduced the first examples of a new family of pH-responsive doubly crosslinked microgel (DX microgels) [Liu et al., Soft Matter, 2011, 7, 4696]. DX microgels are hydrogels composed of covalently-linked functionalised SX microgel particles. DX microgels contain inter-particle crosslinking as well as intra-particle crosslinking. Here, we investigate pH-responsive DX microgels prepared using a new, more versatile, microgel functionalisation strategy. Carbodiimide chemistry is used to vinyl-functionalise poly(MMA/MAA/EGDMA) (methyl methacrylate, methacrylic acid and ethyleneglycol dimethacrylate) microgels (abbreviated as M-EGD). The DX microgels were prepared using pH-triggered inter-penetration of 2-aminoethylmethacrylate (AEM) functionalised SX microgels and free-radical crosslinking. The DX microgels based on M-EGD had built-in microporosity. Furthermore, dynamic rheology data show for the first time that the elastic modulus of DX microgels is proportional to the extent of vinyl group functionalisation. The generality of this approach was demonstrated by the preparation of DX microgels based on poly(EA/MAA/BDD) (ethylacrylate and 1, 4-butanediol diacrylate), which is abbreviated as E-BDD. The pH-responsive DX microgels have high elastic modulus values, swell strongly and have low sol fractions. They are injectable and the DX microgels have improved swelling at low pH which should increase the pH range for potential biomaterial applications. The data are compared with those reported by Liu et al. and the differences discussed.

Synthesis of Hollow Nanospheres Consisting of Amphiphilic Block Copolymers

Abstract Hollow polymeric nanospheres with shells consisting of inner hydrophilic and outer hydrophobic polymer chains are prepared by a surface-initiated living radical polymerization of 2-trimethylsilyloxyethyl acrylate and methyl methacrylate from initiator-modified silica nanoparticles; these nanospheres are subsequently prepared by intraparticle cross-linking and by dissolution of silica matrices with HF. The translation behavior of hydrophilic substrates from an aqueous phase to an oil phase through the nanocapsules is investigated.

Preparation of acrylic copolymers and crosslinking agents and properties as a film

AbstractCopolymers of butyl acrylate (BA)‐methyl methacrylate (MMA)‐acrylic acid (AA) and intraparticle crosslinking agents containing N‐methylol acrylamide (NMA) and ethylene glycol dimethacrylate (EGDMA) were prepared by emulsion copolymerization. After that, films were prepared from the mixture of copolymers and the interparticle crosslinking agents. The interparticle crosslinking agents were prepared from hexamethylene diisocyanate and aziridine ethanol. Mixtures of the copolymer and the interparticle crosslinking agent were cast to films and crosslinked in a convection oven. The effects of the contents of the intra/interparticle crosslinking agents were also evaluated. By increasing the contents of EGDMA, roughness of the films was increased because of the effects of EGDMA acting as an intraparticle crosslinking agent. By increasing the contents of the interparticle crosslinking agent, roughness was also increased by the reaction between the copolymers and interparticle crosslinking agent. Tensile strength and water and chemical resistance of the film were increased, whereas elongation of film was decreased by increasing the contents of interparticle crosslinking agents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Dendritic NanoparticlesThe Impact of Ligand Cross-Linking on Nanocore Stability

This paper describes the synthesis of gold nanoparticles stabilized by two series of new dendritic disulfide ligands with alkene groups at their peripheries. Intraparticle cross-linking of the alkene groups around the periphery of each nanoparticle was achieved by Grubbs' metathesis. It was demonstrated that cross-linking of the organic ligand has no effect on the size or morphology of the inorganic gold core as determined by TEM and UV-vis measurements. However, the introduction of cross-linking at the surface of the ligand enhances the stability of the gold nanocore toward chemical etchant agents (NaCN) and thermal treatment. The impact of cross-linking on nanoparticle stability is greater when the cross-linking is closer to the nanoparticle surface (i.e., using lower generation dendritic ligands). Attempts to perform further synthetic transformation on the hybrid materials in order to remove the gold core led to insoluble products composed predominantly of the dendritic ligand.

One-Step Microwave Preparation of Well-Defined and Functionalized Polymeric Nanoparticles

Well-defined colloidal polymeric nanoparticles are important in advanced biomedical and optical technologies. We report a facile microwave methodology to prepare narrowly dispersed cross-linked polymeric nanoparticles at high solids content through a surfactant-free emulsion polymerization process. The nanoparticle size was controlled by using cross-linkers with enhanced reactivity through a one-step microwaving process, significantly simplifying the nanoparticle synthetic process. The successful size control was realized by confining the cross-linking to intraparticle cross-linking rather than interparticle cross-linking. We also discovered that the superheating/dielectric heating effect associated with microwave irradiation could be utilized to effectively reduce the nanoparticle size.

Preparation of Polyurethane/Acrylic Hybrid Nanoparticles via a Miniemulsion Polymerization Process

Nanosized polyurethane/poly(n-butyl methacrylate) (PU/PBMA) hybrid latex particles (∼50 nm) with various compositions were successfully prepared using a redox-initiated miniemulsion polymerization process. Studies were carried out on the miscibility of PU prepolymer and BMA monomer, PU/BMA droplet formation, and polymerization kinetics. This process provides a new method to synthesize nanosize hybrid latex particles using a relatively small amount of surfactant. A suitable chain extension process was developed, where a hydrophobic chain extender was used to introduce intraparticle cross-linking while maintaining the original small particle size of the nanosize PU/PBMA hybrid latexes. The ratio of PU to BMA, the amount of grafting agent (hydroxyethyl methacrylate; HEMA), and the presence of the hydrophobic chain extender have little influence on the particle size of the final latexes compared to the seeded emulsion polymerization processes. This illustrates the advantage of this process, whereby the final particle size is less sensitive to the composition and amount of cross-linking agent or chain extender.

Nanostructured hybrid materials from aqueous polymer dispersions

Organic–inorganic (O–I) hybrids with well-defined morphology and structure controlled at the nanometric scale represent a very interesting class of materials both for their use as biomimetic composites and because of their potential use in a wide range of technologically advanced as well as more conventional application fields. Their unique features can be exploited or their role envisaged as components of electronic and optoelectronic devices, in controlled release and bioencapsulation, as active substrates for chromatographic separation and catalysis, as nanofillers for composite films in packaging and coating, in nanowriting and nanolithography, etc. A synergistic combination or totally new properties with respect to the two components of the hybrid can arise from nanostructuration, achieved by surface modification of nanostructures, self-assembling or simply heterophase dispersion. In fact, owing to the extremely large total surface area associated with the resulting morphologies, the interfacial interactions can deeply modify the bulk properties of each component. A wide range of starting materials and of production processes have been studied in recent years for the controlled synthesis and characterization of hybrid nanostructures, from nanoparticle or lamellar dispersions to mesoporous materials obtained from templating nanoparticle dispersions in a continuous, e.g. ceramic precursor, matrix. This review is aimed at giving some basic definitions of what is intended as a hybrid (O–I) material and what are the main synthetic routes available. The various methods for preparing hybrid nanostructures and, among them, inorganic–organic or O–I core–shell nanoparticles, are critically analyzed and classified based on the reaction medium (aqueous, non-aqueous), and on the role it plays in directing the final morphology. Particular attention is devoted to aqueous systems and water-borne dispersions which, in addition to being environmentally more acceptable or even a mandatory choice for any future development of large output applications (e.g. in paint, ink and coating industry), can provide the thermodynamic drive for self-assembling of amphiphilics, adsorption onto colloidal particles or partitioning of the hybrid's precursors between dispersed nanosized reaction loci, as in emulsion or miniemulsion free-radical polymerization. While nanoencapsulation and self-assembling processes are already exploited as commercially viable fabrication methods, a newly developed technique based on two-stage sol–gel and free-radical emulsion polymerization is described, which can grant a versatile synthetic approach to hybrid O–I nanoparticles with tailor-made composition of both the organic core and the silica or organosilica shell, and good control on morphology, size and heterophase structure in the 50–500 nm range. Styrene or acrylate homo- and copolymer core latex particles need to be modified with a reactive comonomer, such as trimethoxysilylpropyl methacrylate, to achieve efficient interfacial coupling with the inorganic shell. Accurate control over pH and process conditions is required to avoid latex coagulation or, in case of organic particles with uniform composition, incipient intraparticle crosslinking.

Nanostructured hybrid materials from aqueous polymer dispersions

Organic–inorganic (O–I) hybrids with well-defined morphology and structure controlled at the nanometric scale represent a very interesting class of materials both for their use as biomimetic composites and because of their potential use in a wide range of technologically advanced as well as more conventional application fields. Their unique features can be exploited or their role envisaged as components of electronic and optoelectronic devices, in controlled release and bioencapsulation, as active substrates for chromatographic separation and catalysis, as nanofillers for composite films in packaging and coating, in nanowriting and nanolithography, etc. A synergistic combination or totally new properties with respect to the two components of the hybrid can arise from nanostructuration, achieved by surface modification of nanostructures, self-assembling or simply heterophase dispersion. In fact, owing to the extremely large total surface area associated with the resulting morphologies, the interfacial interactions can deeply modify the bulk properties of each component. A wide range of starting materials and of production processes have been studied in recent years for the controlled synthesis and characterization of hybrid nanostructures, from nanoparticle or lamellar dispersions to mesoporous materials obtained from templating nanoparticle dispersions in a continuous, e.g. ceramic precursor, matrix. This review is aimed at giving some basic definitions of what is intended as a hybrid (O–I) material and what are the main synthetic routes available. The various methods for preparing hybrid nanostructures and, among them, inorganic–organic or O–I core–shell nanoparticles, are critically analyzed and classified based on the reaction medium (aqueous, non-aqueous), and on the role it plays in directing the final morphology. Particular attention is devoted to aqueous systems and water-borne dispersions which, in addition to being environmentally more acceptable or even a mandatory choice for any future development of large output applications (e.g. in paint, ink and coating industry), can provide the thermodynamic drive for self-assembling of amphiphilics, adsorption onto colloidal particles or partitioning of the hybrid's precursors between dispersed nanosized reaction loci, as in emulsion or miniemulsion free-radical polymerization. While nanoencapsulation and self-assembling processes are already exploited as commercially viable fabrication methods, a newly developed technique based on two-stage sol–gel and free-radical emulsion polymerization is described, which can grant a versatile synthetic approach to hybrid O–I nanoparticles with tailor-made composition of both the organic core and the silica or organosilica shell, and good control on morphology, size and heterophase structure in the 50–500 nm range. Styrene or acrylate homo- and copolymer core latex particles need to be modified with a reactive comonomer, such as trimethoxysilylpropyl methacrylate, to achieve efficient interfacial coupling with the inorganic shell. Accurate control over pH and process conditions is required to avoid latex coagulation or, in case of organic particles with uniform composition, incipient intraparticle crosslinking.

Film formation from reactive latex particles: influence of intraparticle crosslinking on mechanical properties

The effects of functional group density of reactive latexes on the relative rates of interdiffusion and crosslinking reaction during film formation and annealing process were investigated. The average diffusion coefficient D of the polymer chain was evaluated from dynamic mechanical analysis and was correlated with the diffusion of polymer chains through particle–particle interfaces. In the film of the reactive particles, the magnitude of D was lower than that of the homopolymer film. These results consistently showed the dependence of chain mobility on tensile strength development of the film of the reactive latexes, in which the mobility of the chains was restricted, leading to the prevention of mechanical strength development.

Interfacial aspects of strength development in poly(methyl methacrylate)‐based latex systems

AbstractFilm formation from poly(methyl methacrylate) (PMMA) latex and PMMA copolymer latex incorporating N‐(iso‐butoxymethyl)acrylamide (IBMA) or methacrylic acid (MAA) has been investigated in terms of the development of tensile strength as a function of annealing time and temperature. Tensile strength is developed through a combination of macromolecular interdiffusion and interfacial crosslinking. The relative rates of interdiffusion vs. crosslinking reactions were studied as a function of temperature and the chemical nature and concentration of the IBMA and MAA functional groups. For low concentrations of these two functional monomers it appears that polymer chain interdiffusion between adjacent latex particles during the film formation process dominates the kinetics of strength development. However, at higher IMBA and MAA concentrations, the higher glass transition temperature at the latex particle surface and intraparticle crosslinking hinders interdiffusion, as reflected by differences in the power law exponent values obtained from the log‐log dependence of tensile strength on annealing time. The power law exponents were higher in the case of PMMA than for both IBMA‐ and MAA‐containing copolymers. There was a greater influence temperature on the tensile behavior for the MAA copolymer system as compared to the IBMA copolymer. In the interfacially crosslinked latex polymer system, there is competition between the interdiffusion and crosslinking mechanisms in determining the final mechanical strength of films during the annealing process. © 1995 John Wiley & Sons, Inc.

A method to determine the most suitable model of coagulation regarded as a gelation process

A method to investigate the characteristics of a geling system is presented. It is known that gelation time is prolonged from the value predicted by the Flory-Stockmayer model because of intraparticle cross-linking. Another effect should be taken into consideration. If hard particles are formed in the course of the reactions, the functional groups buried in the inner part of the particles may find it difficult to participate in the interparticle cross-linking. This effect is studied using the coagulation kinetics