An emulsifier‐free core–shell polyacrylate/diacetone acrylamide emulsion with nano‐SiO2 for room temperature curable waterborne coatings

An emulsifier‐free core–shell polyacrylate emulsion, containing nano‐SiO₂ nanoparticles in the core and diacetone acrylamide (DAAM) in the shell, has been successfully prepared by emulsifier‐free seeded emulsion polymerization. The effects of reaction temperature, dropping time, nano‐SiO₂ and initiator contents, and variation of the composition of core monomers on the amount of coagulum, particle size, and monomer conversion have been investigated. The particle morphology and the distribution of emulsion particles have been measured by transmission electron microscopy (TEM) and dynamic light scattering. The keto‐carbonyl groups on the surface of the polyacrylate emulsion nanoparticles reacted with adipic dihydrazide (ADH) to form a film with a cross‐linked network structure at room temperature. Therefore, the emulsifier‐free core–shell emulsion could be used as a two‐component room temperature curable waterborne coating. It was also found that the properties of the coating were clearly superior after using the cross‐linker. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of polytetrafluoroethylene/polyacrylate core-shell nanoparticles via emulsifier-free seeded emulsion polymerization

Polytetrafluoroethylene (PTFE)/polyacrylate core-shell nanoparticles were produced via the emulsifier-free seeded emulsion polymerization of acrylate monomers with PTFE latex as seed. The monomer conversions under different synthesis parameters were monitored by a gravimetric method. The polymerization conditions for preparing PTFE/polyacrylate core-shell nanoparticles were surveyed and optimized. The chemical component of the PTFE/polyacrylate particles was confirmed by comparing the Fourier-transform infrared spectra of PTFE and PTFE/polyacrylate particles. The core-shell structure of the resulting PTFE/polyacrylate nanocomposite particles was investigated by transmission electron microscopy. The water contact angles of the films prepared from PTFE/polyacrylate nanocomposite particles showed that the films were hydrophilic, which confirmed that polyacrylate covered the surface of the PTFE particles. This kind of PTFE/polyacrylate core-shell nanoparticles might advance the compatibility of PTFE with other materials due to the covering of the polyacrylate shell on the surface of PTFE, which would make them promising in various fields.     

PMMA‐based core‐shell nanoparticles with various PTFE cores

Polytetrafluoroethylene (PTFE) latices with spherical and rod‐like particles in the submicrometer size range, were employed as seeds in the emulsifier‐free methylmethacrylate (MMA) emulsion polymerization to obtain PTFE‐polymethylmethacrylate (PMMA) core‐shell nanoparticles. Stable latices were generally obtained. No residual PTFE was found at the end of the reaction. By appropriately choosing the ratio between MMA and PTFE in the reaction mixture, particles with predetermined size and monodisperse or narrow size distribution were prepared. The high structural regularity of the core‐shell samples allows the preparation of film with a periodic distribution of the cores thus ultimately leading to a well structured 2D colloidal crystal. A very peculiar crystallization behavior was observed because of the PTFE compartmentalization in the composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2928–2937, 2009     

Synthesis and characterization of fluorine‐containing polyacrylate latex with core–shell structure by UV‐initiated seeded emulsion polymerization

A core–shell fluorine‐containing polyacrylate emulsion was successfully prepared by UV‐initiated seeded emulsion polymerization in two stages in the presence of two photoinitiators. The water‐soluble photoinitiator for the core polymerization and the oil‐soluble photoinitiator was used for the shell polymerization. Both of the two stage polymerizations could be completed within 15 min and displayed a conversion above 94%. The emulsion and the films were characterized by Fourier transformed infrared spectrometry, transmission electron microscopy, dynamic light scattering, X‐ray photoelectron spectroscopy (XPS), contact angle (CA), and thermogravimetry analysis, respectively. The analysis results indicated that the fluorine‐containing latex particles had very small particle size (40 nm) with a core–shell structure and a narrow particle size distribution. XPS analysis revealed that a gradient concentration of fluorine excited in fluorine‐containing emulsion film from the film–air interface to the film–glass interface. In addition, the film formed from the fluorine‐containing emulsion exhibited not only higher thermal stability but also better hydrophobicity than that of the fluorine‐free emulsion. Copyright © 2010 John Wiley & Sons, Ltd.     

Preparation of epoxy‐functionalized polystyrene/silica core–shell composite nanoparticles

Epoxy‐functionalized polystyrene/silica core–shell composite nanoparticles were prepared by the postaddition of glycidyl methacrylate (GMA) via emulsion polymerization. The outermost shell of obtained multilayered core–shell particles was made up of poly(glycidyl methacrylate) (PGMA). A semicontinuous process involving the dropwise addition of GMA was used to avoid demulsification of the emulsion system. The amount of grafted PGMA was quantified by Fourier transform infrared spectroscopy and was altered in a wide range (1–50 wt % to styrene). The binding efficiency was usually high (ca. 90%), indicating strong adhesion between the silica core and the polymer shell. There were approximately four or five original silica beads, which formed a cluster, per composite of nanoparticles whose size was about 60–70 nm. Other main factors of polymerization conditions including the amounts of sodium dodecyl sulfonate and silica are also discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2253–2262, 2004     

Preparation and properties of polytetrafluoroethylene-modified polyacrylate via emulsion polymerization

One method of preparation of polytetrafluoroethylene(PFTE)-modified polyacrylate emulsion has been studied. Through pre-emulsion technology, PTFE powder could be dispersed by high speed shearing with high-speed dispersor. PFTE-modified polyacrylate has been prepared by in situ copolymerization of n-butyl acrylate, n-methyl methacrylate, n-styrene, and α-methacrylic acid in the presence of seed particles of dispersed PTFE by semi-starved addition method. The properties of the emulsion under various polymerization conditions were investigated. The morphology of the latex particles with about 180 nm were observed by scanning electron microscopy (SEM). It was shown that the particles with linear PTFE/core–polyacrylate/shell could eventually be dispersed homogeneously. TG showed that the heat-stability was improved obviously.     

Two‐dimensional non‐close‐packed arrays of nanoparticles via core‐shell nanospheres and reactive ion etching

Nanosized PTFE/polystyrene core‐shell particles were prepared by seed emulsion polymerization technique starting from PTFE seeds of 20 nm. At the end of the reaction, no residual PTFE nor secondary nucleation was observed and by appropriately choosing the ratio between the monomer and the PTFE seed it was possible to obtain particles, with predetermined size in the range 60–100 nm, featuring an extremely narrow size distribution. These particles were successfully employed as building blocks for the preparation of large scale nanosized monolayers through the floating technique. Reactive ion etching was further applied to modulate the size characteristics of the resulting 2D ordered nanostructure. Although for relatively short RIE times a peculiar continuous morphology was observed in which the particles are interconnected through thin arms, on further increasing the RIE time a well‐organized 2D arrangement of particles with size of about 30 nm was obtained. Considering the shell as an expendable ordering and spacing tool, the use of core‐shell nanospheres allows a wide variety of controlled morphologies to be designed and prepared thus opening new perspectives for nanostructure fabrication processes through nanosphere lithography (NSL). Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication and Characterization of Sulfonate‐containing Polystyrene/CaCO3 Core‐shell Nanoparticles

Polystyrene (PSt) seed latex was first prepared via soap‐free emulsion polymerization in the presence of a small amount of methacrylic acid using ammonium persulfate as initiator, and then seeded emulsion polymerization of sodium 4‐styrenesulfonate (NaSS) and St was carried out to synthesize P(St‐NaSS) core latex using 2,2′‐azobisisobutyronitrile as initiator. After that, P(St‐NaSS)/CaCO₃ core‐shell nanoparticles were fabricated by sequentially introducing Ca(OH)₂ aqueous solution and CO₂ gas into the core latex. The morphology of the core and core‐shell nanoparticles was characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM), and the state of CaCO₃ shell was confirmed with high‐resolution scanning transmission electron microscope (HR‐STEM) and selected area electron diffraction (SAED). Results showed that PNaSS chains were successfully grafted onto the PSt seed surface, and length of the PNaSS "hairs" could be modulated by adjusting NaSS amount. Sulfonic groups of the PNaSS hairs served as additives in the formation and stabilization of amorphous CaCO₃(ACC) and prevented ACC from sequent transformation into crystalline states. The amount of the anchored CaCO₃ increased with the growth of PNaSS hair length, and reached 51 wt% (by thermalgravimetric analysis) under the optimal encapsulating temperature of 45°C. Moreover, the forming mechanism of P(St‐NaSS)/CaCO₃ core‐shell nanoparticles was proposed.     

Optically active core/shell nanoparticles prepared using self‐assembled polymer micelle as reactive nanoreactor

This article reports on optically active core/shell nanoparticles constituted by chiral helical polymers and prepared by a novel approach: using self‐assembled polymer micelles as reactive nanoreactors. Such core/shell nanoparticles were composed of optically active helical‐substituted polyacetylene as the core and thermosensitive poly(N‐isopropylacrylamide) as the shell. The synthetic procedure is divided into three major steps: (1) synthesis of amphiphilic diblock copolymer bearing polymerizable C[tbond]C bonds via atom transfer radical polymerization, followed by (2) self‐assembly of the diblock copolymer to form polymer micelles; and (3) catalytic emulsion polymerization of substituted acetylene monomer conducted using the polymer micelles as reactive nanoreactors leading to the core/shell nanoparticles. The core/shell nanoparticles simultaneously exhibited remarkable optical activity and thermosensitivity. The facile, versatile synthesis methodology opens new approach toward preparing novel multifunctional core/shell nanoparticles.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation of composite polyacrylate latex particles with in situ‐formed methylsilsesquioxane cores

Composite polyacrylate latex particles were prepared through a simple method by dissolving organosilicon monomer methyltrimethoxysilane in a monomer mixture of acrylic monomers methyl methacrylate (MMA), n‐butyl acrylate (n‐BA), and acrylic acid (AA). With the addition of water needed for hydrolysis, methyltrimethoxylsilane hydrolyzed under catalysis by AA and further condensed to form polymeric methylsilsesquioxane (MSQ). The monomer mixture containing in situ‐formed MSQ was then subjected to emulsification and emulsion polymerization. Transmission electron microscopy (TEM) images showed that the obtained latex particles had a core–shell structure. Differences between the X‐ray photoelectron spectroscopy (XPS) results of the contents of silicon atoms on surfaces of films formed at temperatures above and below glass transition temperatures (T_gs) of polyacrylate evidenced that the cores were made up of MSQ and the shells were made up of polyacrylate. The static water contact angle measurements indicated that the incorporation of MSQ can result in composite latex with higher hydrophobicity. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation of poly(methyl methacrylate)–poly(acrylonitrile‐co‐butadiene) core–shell nanoparticles

Poly(methyl methacrylate)–poly(acrylonitrile‐co‐butadiene) (PMMA–NBR) core–shell structured nanoparticles were prepared using a two‐stage semibatch microemulsion polymerization system with PMMA and NBR as the core and shell, respectively. The Gemini surfactant 12‐3‐12 was used as the emulsifier and found to impose a pronounced influence on the formation of core–shell nanoparticles. The spherical morphology of core–shell nanoparticles was observed. It was found that there exists an optimal MMA addition amount, which can result in the minimized size of PMMA–NBR core–shell nanoparticles. The formation mechanism of the core–shell structure and the interaction between the core and shell domains was illustrated. The PMMA–NBR nanosize latex can be used as the substrate for the following direct latex hydrogenation catalyzed by Wilkinson's catalyst to prepare the PMMA–HNBR (hydrogenated NBR) core–shell nanoparticles. The hydrogenation rate is rapid. In the absence of any organic solvent, the PMMA–HNBR nanoparticles with a size of 30.6 nm were obtained within 3 h using 0.9 wt % Wilkinson's catalyst at 130 °C under 1000 psi of H₂. This study provides a new perspective in the chemical modification of NBR and shows promise in the realization of a “green” process for the commercial hydrogenation of unsaturated elastomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Fabrication of monodisperse luminescent nanoparticles with core/shell poly(styrene/thiophene) structure

Luminescent poly(styrene/thiophene) (PSt/PT) core/shell nanoparticles were prepared by oxidative polymerization in the presence of PSt seed particles. PSt seed particles with uniform size distribution were prepared with an anionic surfactant by an emulsion polymerization process, and were used as a template to prepare monodispersive PT‐coated nanoparticles. A luminescent Polythiophene (PT) layer was formed on the surface of PSt nanoparticles by oxidation polymerization with iron chloride (FeCl₃) and hydrogen peroxide (H₂O₂). The mechanism of core/shell formation was found to be the interface‐dominant polymerization induced by the electrostatic attraction between the sulfonate group of anionic surfactant and Fe³⁺ ions after the diffusion of thiophene monomer to the PSt nanoparticles. Field‐emission scanning electron microscopy and transmission electron microscopy (TEM) proved the core/shell structure, which provided key evidence that PT was incorporated onto the surface of PSt nanoparticles. In addition, the effect of the PT shell thickness on photoluminescent (PL) intensity was investigated by changing the shell thickness of PSt/PT nanoparticles. We observed that the PL intensity increased up to about 30 nm of PT shell thickness, and then decreased due to self‐absorption. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5968–5975, 2008     

Synthesis of single‐core and multiple‐core core‐shell nanoparticles by RAFT emulsion polymerization: Lead sulfide‐copolymer nanocomposites

We report here a simple and direct route for the preparation of lead sulfide (PbS) quantum dots (QDs) embedded into polymeric nanospheres by emulsion polymerization. In this process, QDs are first dispersed in an aqueous solution containing a statistical oligomer constituted of five butyl acrylate and ten acrylic acid units prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using a trithiocarbonate as RAFT agent. Then, the dispersion of PbS QDs is engaged into an emulsion polymerization process to form core‐shell nanoparticles. Transmission electron microscopy reveals the presence of single‐core core‐shell particles at low concentration of PbS QD, whereas multiple‐core core‐shell particles containing either well separated or aggregated PbS QDs are formed at high concentration of PbS QDs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Magnetite‐polylactic acid core–shell nanoparticles by ring‐opening polymerization under microwave irradiation

The synthesis of magnetic core–shell nanoparticles consisting of magnetite cores surface‐functionalized by glycolic acid covered by polylactic acid was performed by applying the “grafting‐from” strategy, where the polymerization is initiated from the particle surface. The surface initiated ring‐opening polymerization of D,L ‐lactide was initiated by tin (II) 2‐ethylhexanoate using microwave irradiation. Core–shell nanoparticles of high colloidal stability in water were obtained in this way. The morphology of the magnetic core–shell nanostructure was determined by transmission electron microscopy, and the chemical structure was elucidated by Fourier transform infrared spectroscopy (FTIR) and X‐ray photoelectron spectroscopy. Magnetic measurements revealed superparamagnetic behavior and high magnetization values. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

One‐stage synthesis of narrowly dispersed polymeric core‐shell microspheres

A method of one‐stage soap‐free emulsion polymerization to synthesize narrowly dispersed core‐shell microspheres is proposed. Following this method, core‐shell microspheres of poly(styrene‐co‐4‐vinylpyridine), poly(styrene‐co‐methyl acrylic acid), and poly[styrene‐co‐2‐(acetoacetoxy)ethyl methacrylate‐co‐methyl acrylic acid] are synthesized by one‐stage soap‐free emulsion polymerization of a mixture of one or two hydrophobic monomers and a suitable hydrophilic monomer in water. The effect of the molar ratio of the hydrophobic monomer to the hydrophilic one on the size, the core thickness, and the shell thickness of the core‐shell microspheres is discussed. The molar ratio of the hydrophobic and hydrophilic monomers and the hydrophilicity of the resultant oligomers of the hydrophilic monomer are optimized to synthesize narrowly dispersed core‐shell microspheres. A possible mechanism of one‐stage soap‐free emulsion polymerization to synthesize core‐shell microspheres is suggested and coagglutination of the oligomers of the hydrophilic monomers on the hydrophobic core is considered to be the key to form core‐shell microspheres. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1192–1202, 2008     

Cross‐Linking Density and Temperature Effects on the Self‐Assembly of SiO2—PNIPAAm Core–Shell Particles at Interfaces

SiO₂–PNIPAAm core–shell microgels (PNIPAAm=poly(N‐isopropylacrylamide)) with various internal cross‐linking densities and different degrees of polymerization were prepared in order to investigate the effects of stability, packing, and temperature responsiveness at polar–apolar interfaces. The effects were investigated using interfacial tensiometry, and the particles were visualized by cryo‐scanning electron microscopy (SEM) and scanning force microscopy (SFM). The core–shell particles display different interfacial behaviors depending on the polymer shell thickness and degree of internal cross‐linking. A thicker polymer shell and reduced internal cross‐linking density are more favorable for the stabilization and packing of the particles at oil–water (o/w) interfaces. This was shown qualitatively by SFM of deposited, stabilized emulsion droplets and quantitatively by SFM of particles adsorbed onto a hydrophobic planar silicon dioxide surface, which acted as a model interface system. The temperature responsiveness, which also influences particle–interface interactions, was investigated by dynamic temperature protocols with varied heating rates. These measurements not only showed that the particles had an unusual but very regular and reversible interface stabilization behavior, but also made it possible to assess the nonlinear response of PNIPAAm microgels to external thermal stimuli.     

聚氨酯/聚丙烯酸酯复合乳液的研制进展

概述聚氨酯－聚丙烯酸酯复合乳液的制备方法。特别对聚氨酯－聚丙烯酸酯复合乳液共聚法作了较为系统的介绍和讨论。     

Immobilization of RAFT agents on silica nanoparticles utilizing an alternative functional group and subsequent surface‐initiated RAFT polymerization

Silica–polystyrene core‐shell particles were successfully prepared by surface‐mediated reversible addition fragmentation chain transfer (RAFT) polymerization of styrene monomer from the surfaces of the silica‐supported RAFT agents. Initially, macro‐RAFT agents were synthesized by RAFT polymerization of γ‐methacryloxypropyltrimethoxysilane (MPS) in the presence of chain transfer agents (CTAs). Immobilization of CTAs onto the silica surfaces was then performed by reacting silica with macro‐RAFT agents via a silane coupling. Grafting of polymer onto silica forms core‐shell nanostructures and shows a sharp contrast between silica core and polymer shell in the phase composition. The thickness of grafted‐polymer shell and the diameter of core‐shell particles increase with the increasing ratio of monomer to silica. A control experiment was carried out by conventional free radical emulsion copolymerization of MPS‐grafted silica and styrene under comparable conditions. The resulting data provide further insight into the chemical composition of grafted‐polymers that are grown from the silica surface through RAFT process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 467–484, 2009     

Scalable and Recyclable All‐Organic Colloidal Cascade Catalysts

We report on the synthesis of core–shell microparticles (CSMs) with an acid catalyst in the core and a base catalyst in the shell by surfactant‐free emulsion polymerization (SFEP). The organocatalytic monomers were separately copolymerized in three synthetic steps allowing the spatial separation of incompatible acid and base catalysts within the CSMs. Importantly, a protected and thermo‐decomposable sulfonate monomer was used as acid source to circumvent the neutralization of the base catalyst during shell formation, which was key to obtain stable, catalytically active CSMs. The catalysts showed excellent performance in an established one‐pot model cascade reaction in various solvents (including water), which involved an acid‐catalyzed deacetalization followed by a base‐catalyzed Knoevenagel condensation. The CSMs are easily recycled, modified, and their synthesis is scalable, making them promising candidates for organocatalytic applications.     

A Facile Synthesis of Cu NPs and Ag NPs Coated by PS with Core–Shell Structure by Precipitation Polymerization

Copper nanoparticles (Cu NPs ) coated with polystyrene (PS ) (Cu NPs @PS ) were prepared by precipitation polymerization. First, Cu NPs were prepared by chemical reduction using cupric acetate as precursor, sodium polyacrylate (PAANa ) as stabilizer, and hydrazine hydrate as reducing agent. Then Cu NPs were coated by precipitation polymerization using styrene as monomer, 3‐(trimethoxysilyl) propyl acrylate as co‐monomer, and 2, 2‐azobisisobutyronitrile (AIBN ) as initiator. Ultraviolet–visible (UV –vis) spectroscopy and transmission electron microscopy (TEM ) results showed that stable composite particles could be synthesized by precipitation polymerization. The amount of PAANa had a significant effect on the size of Cu NPs . The addition of more PAANa resulted in smaller Cu NPs . The spherical Cu NPs became nanowires when increasing the stirring rate from 350 to 700 rpm during precipitation polymerization. Ag NPs @PS with core–shell structure were also prepared by this method, which appears to be universal.