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     

Influence of the Sacrificial Polystyrene Removal Pathway on the TiO2 Nanocapsule Structure

This study demonstrates the significant influence of the polystyrene removal pathway on the TiO₂ nanocapsules obtained from PS @TiO₂ core‐shell particles. In a first step, the polystyrene spheres were coated with titanium oxide via hydrolysis and condensation of the titanium precursor to form PS @TiO₂ core‐shell particles. Then, the creation of the empty cavity to form TiO₂ nanocapsules was achieved by removing the polystyrene template by i ) thermal decomposition of the polystyrene or ii ) dissolution of the polystyrene using Soxhlet extractor followed by a thermal procedure. These pathways to remove the polystyrene were investigated by thermogravimetric studies, IR spectroscopy, transmission and scanning electron microscopy and powder X‐ray diffraction. The final TiO₂ nanocapsule structure strongly depends on the sacrificial polystyrene removal pathway. The preservation of the TiO₂ nanocapsules was obtained essentially when the polystyrene was dissolved before the crystallization of the TiO₂.     

Latex and hollow particles of reactive polypyrrole: preparation, properties, and decoration by gold nanospheres

Polypyrrole-coated polystyrene latex particles bearing reactive N-amino functional groups (PS-PPyNH2) were prepared by the in-situ copolymerization of pyrrole (Py) and the active amino-functionalized pyrrole (PyNH2) in the presence of 1.33 microm-diameter polystyrene (PS) latex particles. These particles were prepared by dispersion polymerization of styrene using poly(N-vinylpyrrolidone), PNVP, as a steric stabilizer. The functionalized polypyrrole-coated PS particles (PS-PPyNH2) were characterized in terms of their particle size and surface morphology using transmission electron microscopy (TEM). Infrared and X-ray photoelectron spectroscopy (XPS) detected pyrrole-NH2 repeat units at the surface of the latex particles, indicating that this monomer had indeed copolymerized with pyrrole. The core-shell structure of the PS-PPyNH2 particles was confirmed by etching the polystyrene core in THF, leading to the formation of hollow conducting polymer capsules. The PS-PPyNH2 particles were then decorated with citrate-stabilized gold nanoparticles via electrostatic interactions. Furthermore, etching of the polystyrene core resulted in the formation of gold-decorated PPyNH2 hollow capsules.     

The volume transition in thermosensitive core-shell latex particles investigated by small-angle x-ray scattering and dynamic light scattering

We present a survey over recent studies of the volume transition in colloidal core-shell particles composed of a solid poly(styrene) core and a shell of a thermosensitive crosslinked polymer chains. The thermosensitive shell is built up from poly(N-isopropylacrylamide) chains (PNIPA) crosslinked by N,N′-methylenbisacrylamide (BIS). In addition, particles containing acrylic acid (AA) as comonomer have been synthesized and investigated. The volume transition of these particles have been studied by dynamic light scattering (DLS) and by small-angle X-ray scattering (SAXS). In all cases analyzed so far the volume transition was found to be continuous. This finding shows that the core-shell microgels behave in a distinctively different manner than ordinary thermosensitive gels: The crosslinked chains in the shell are bound to a solid boundary independent of temperature. The spatial constraint by this boundary decreases the maximum degree of swelling but also prevents a full collapse of the network above the volume transition.     

Ag Nanocomposite Particles: Preparation,Characterization and Application

Summary Herein, we report that different core-shell particles could be successfully used as the carrier systems for the deposition of silver nanoparticles. Firstly, thermosensitive core-shell microgel particles have been used as the carrier system for the deposition of Ag nanoparticles, in which the core consists of poly (styrene) (PS) whereas the shell consists of poly (N-isopropylacrylamide) (PNIPA) network cross-linked by N, N′-methylenebisacrylamide (BIS). Immersed in water the shell of these particles is swollen. Heating the suspension above 32 °C leads to a volume transition within the shell, which is followed by a marked shrinking of the network of the shell. Secondly, “nano-tree” type polymer brush can be used as “nanoreactor” for the generation of silver nanoparticles also. This kind of carrier particles consists of a solid core of PS onto which bottlebrush chains synthesized by the macromonomer poly (ethylene glycol) methacrylate (PEGMA) are affixed by “grafting from” technique. Thirdly, silver nanoparticles can be in-situ immobilized onto polystyrene (PS) core-polyacrylic acid (PAA) polyelectrolyte brush particles by UV irradiation. Monodisperse Ag nanoparticles with diameter of 8.5 nm, 7.5 nm and 3 nm can be deposited into thermosensitive microgels, “nano-tree” type polymer brushes and polyelectrolyte brush particles, respectively. Moreover, obtained silver nano-composites show different catalytic activity for the catalytic reduction of p-nitrophenol depending on the carrier system used for preparation.     

Preparation of multilayered gold-silica-polystyrene core-shell particles by seeded polymerization

A preparation method for multilayered gold-silica-polystyrene core-shell composite particles is proposed. The gold-silica core-shell particles of 192-nm-sized, synthesized by coating the 18-nm-sized gold particles with silica by a seeded growth technique, were used as cores for succeeding polystyrene coating. After surface modification of gold-silica composite particles by methacryloxypropyltrimethoxysilane (MPTMS), polymerizations of styrene (0.16-0.4 M) were conducted with 8 x 10(-3) M of potassium persulfate initiator in the presence of 1 x 10(-3) M of sodium p-styrenesulfonate anionic monomer. Multilayered core-shell gold-silica-polystyrene particles that contained a single core could be obtained. The coefficient of variation of size distribution (CV) of the composite particles was less than 7%, and polystyrene shell thickness was in a range of 193 to 281 nm.     

壳层可控导电聚吡咯/聚苯乙烯复合微球及聚吡咯中空微胶囊的制备

在导电聚合物含量较小时,含核壳结构的导电聚合物复合粒子就可以具有和本体相当的导电率,且加工性好,近年来这种核壳结构微粒的制备已引起了科学家们的广泛关注．Armes等[制备了导电聚吡咯、导电聚苯胺包覆聚苯乙烯的核壳结构胶体粒子及聚苯胺和二氧化硅的纳米复合物．刘正平等用改进的方法在粒径为116nm的单分散聚苯乙烯乳胶粒子上包覆聚吡咯,     

Preparation of temperature-sensitive polymer particles having different lower critical solution temperatures

Preparation of temperature-sensitive core-shell composite polymer particles was carried out by seeded emulsion copolymerization of dimethylaminoethyl methacrylate and ethylene glycol dimethacrylate with submicron-sized polystyrene seed particles as core. The lower critical solution temperature (LCST) of the core-shell composite was about 35°C, while the LCST could be controlled toward higher or lower temperatures by copolymerizing the shell layer with hydrophilic/hydrophobic vinyl comonomer.     

Synthesis of core-shell type polystyrene monodisperse particles with chloromethyl groups

The synthesis of core-shell type polystyrene monodisperse particles with surface chloromethyl groups was carried out by a two-step emulsion polymerization process at different reaction temperatures. In a first step, the core was synthesized at 90 °C by means of batch emulsion polymerization of styrene (St), and in the second step, the shell was polymerized by batch emulsion copolymerization of St and chloromethylstyrene (CMS) using the seed obtained previously. With the aim of optimizing the production of these core-shell type polystyrene monodisperse particles with surface chloromethyl groups, the reaction temperature in the second step, the purification or not of the functionalized monomer (CMS), the amount and type of the redox initiator system used, and the type of addition of the initiator system to the reactor were studied.     

Synthesis of polymer particles possessing radical initiating sites on the surface by emulsion copolymerization and construction of core–shell structures by a photoinduced atom transfer radical polymerization approach

The crosslinked polystyrene particles possessing photofunctional N,N‐diethyldithiocarbamate groups on their surface were prepared by free‐radical emulsion copolymerization of a mixture of styrene, divinylbenzene and 4‐vinylbenzyl N,N‐diethyldithiocarbamate with redox system as an initiator under UV irradiation. In this copolymerization, the inimer 4‐vinylbenzyl N,N‐diethyldithiocarbamate acted the formation of hyperbranched structures by living radical photopolymerization. The particle sizes (number‐average particle diameter = 214–523 nm) were controlled by varying the feed amount of surfactant and size distributions were relatively narrow. Subsequently, core–shell particles were synthesized by photoinduced atom transfer radical polymerization approach of methyl methacrylate initiated by photofunctional polystyrene particles as a macroinitiator. Such core–shell particles were stabilized sterically by grafted chains in organic solvents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1771–1777, 2007     

Synthesis of ZnO/polystyrene composites particles by Pickering emulsion polymerization

ZnO/polystyrene composite particles were synthesized by Pickering emulsion polymerization. ZnO nanoparticles were first prepared by reaction of zinc acetate and sodium hydroxide in ethanol medium. Then different amount of styrene monomer was emulsified in water in the presence of ZnO nanoparticles either by mechanical stirring or by sonication, followed by polymerization of styrene. Two kinds of initiators were used to start the polymerization, azobisisobutyronitrile (AIBN) and potassium persulfate (KPS). The X-ray diffraction pattern verified the crystal structure of ZnO and FT-IR spectra evidenced the existence of ZnO and polystyrene (PS) in ZnO/polystyrene composite particles. Different morphologies were observed for the composite particles when using different initiators. From TEM photographs, AIBN-initiated system produced mainly core-shell composite particles with PS as core and ZnO as shell, while KPS-initiated system showed both composite particles and pure PS particles. Two schemes of reaction mechanism were proposed to explain the morphologies accordingly. Both systems of composite particles showed good pH adjusting ability.     

Semi-continuous emulsion polymerization of styrene in the presence of poly(methyl methacrylate) seed particles. Polymerization conditions giving core-shell particles

This work reports the morphology of two-phase latex particles prepared by semi-continuous seed emulsion polymerization of styrene in the presence of polar poly(methyl methacrylate), PMMA, seed particles, using different conditions of non-polar styrene feed rate, rate of initiation, seed particle concentration and temperature of polymerization.The expected latex particle morphology at thermodynamic equilibrium is an inverted core-shell structure where the non-polar polystyrene would form the core. However, depending on the set of process conditions used the morphology of the resulting two-phase particles varied from that of a pure core-shell structure, over intermediate structures in which a shell of PS surrounded a PMMA core containing an increasing number of PS phase domains, to a structure in which the entire PS phase was present as discrete PS phase domain, more or less evenly distributed in a matrix of PMMA.By the use of a caloirimetric reactor system the monomer concentration in the particles during the different polymerization experiments could be calculated by comparing the integral of the polymerization rate curve with the integral of the monomer feed rate. A comparison between particle morphology and the calculated concentration of plasticizing monomer in the polymerizing particles strongly suggested that the diffusivity of the entering oligo radicals determined by the difference between polymerization temperature and the glass transition temperature of the monomer-swollen core polymer is a key factor determining the morphology of two-phase particles prepared by semi-continuous seed emulsion polymerization.Two-phase particles with a true core-shell structure were obtained in experiments where the estimated glass transition temperature of the PMMA phase was only a few degrees below the polymerization temperature. The results show that such particles can be obtained under conditions of high as well as low styrene feed rates, provided that the rate of initiation is properly adjusted.     

Acetal-functionalized polymer particles useful for immunoassays

The synthesis of core-shell type polystyrene monodisperse particles with surface acetal groups was carried out by a two-step emulsion polymerization process. In a first step, the core was synthesized by batch emulsion polymerization of styrene (St), and in the second step, the shell was polymerized by batch emulsion terpolymerization of styrene, methacrylic acid (MAA), and methacrylamidoacetaldehyde dimethyl acetal (MAAMA), using the seed obtained previously. With the aim of analyzing the effect of the thickness of the shell, the pH of the reaction medium and the weight ratio of the termonomers to prepare the shell, on the amount of the functionalized groups, several core-shell type latex particles were synthesized by two-step emulsion polymerization in a batch reactor. The latexes were characterized by TEM and conductimetric titration to obtain the particle size distribution and the amount of carboxyl and acetal groups on the surface, respectively. Looking for the applicability of the synthesized latexes in immunoassays, IgG a-CRP rabbit antibody was covalently bonded to the surface of the particles synthesized in neutral medium. The complex latex-protein was immunologically active against the CRP antigen. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1605–1610, 1997     

Synthesis and Characterization of Polystyrene/Nanosilica Organic-Inorganic Hybrid

IntroductionIn the past two decades, because of its potentialindustrial applications, organic-inorganic compositeshave attracted the attention of both researchers andacademicians. Organic-inorganic hybrids offer the pos-sibility to combine both the advant…     

Preparation of core–shell composite polymer particles by a novel heterocoagulation based on hydrophobic interaction

Submicron-sized cationic polystyrene shell particles with active ester groups were effectively self-assembled on hydrophobic surfaces of cross-linked polystyrene (PST) particles, uncharged core particles with ca. 8.5-µm diameter in aqueous systems. The hydrophobic interactions between the shell particles and core particles play a key role in heterocoagulation. The resulting heterocoagulates were highly physically stable in water, and the morphology was controlled by several factors including the solid content of latex, self-assembling time, and electrolyte concentration. Composite polymer particles with a core–shell structure were successfully obtained from the heterocoagulates by heat treatment for 3 h at a temperature above the glass transition temperature (T_g) of the cationic polymer shell particles.     

Encapsulation of uranyl acetate molecules using hollow polymer templates

Crosslinking 4-mercaptostyrene ligands used to protect gold nanoclusters led to a core-shell structure containing a nanometer-sized gold center surrounded with a layer of polystyrene. Sodium cyanide etching of gold from these polymer/gold composite particles generated polymer nanocapsules that were used as hollow templates for encapsulation of uranyl acetate.     

Polystyrene‐Core–Silica‐Shell Hybrid Particles Containing Gold and Magnetic Nanoparticles

Polystyrene‐core–silica‐shell hybrid particles were synthesized by combining the self‐assembly of nanoparticles and the polymer with a silica coating strategy. The core–shell hybrid particles are composed of gold‐nanoparticle‐decorated polystyrene (PS‐AuNP) colloids as the core and silica particles as the shell. PS‐AuNP colloids were generated by the self‐assembly of the PS‐grafted AuNPs. The silica coating improved the thermal stability and dispersibility of the AuNPs. By removing the “free” PS of the core, hollow particles with a hydrophobic cage having a AuNP corona and an inert silica shell were obtained. Also, Fe₃O₄ nanoparticles were encapsulated in the core, which resulted in magnetic core–shell hybrid particles by the same strategy. These particles have potential applications in biomolecular separation and high‐temperature catalysis and as nanoreactors.     

Synthesis and characterization of epoxy-functional polystyrene particles

Colloidal polystyrene particles with surface epoxy groups have been synthesized through surfactant-free emulsion copolymerization of styrene with glycidyl methacrylate; and through copolymerization of glycidyl methacrylate (GMA) and methyl methacrylate as shells around existing polystyrene seed particles. We developed two titration methods to quantify the number of epoxy groups that survived the polymerization processes. The styrene-GMA copolymer particles were judged to be unsatisfactory as model colloidal materials due to their size polydispersity and unknown internal distribution of epoxy groups. The core-shell particles had high epoxy surface densities with at least 60% of the initial epoxy groups surviving the synthesis process. Transmission electron microscopy shows that the thickness of the epoxy-rich shell is less than expected based on the volume of monomers added, suggesting that some of the monomer forms water-soluble oligomers. Photon correlation spectroscopy measurements imply that the shell is swollen with water and consists of polymer configurations which extend out into solution. The morphological details vary consistently with the GMA content, and hence the hydrophilicity, of the shell polymer. © 1995 John Wiley & Sons, Inc.     

单分散聚丙烯酸丁酯-二氧化硅核壳粒子的制备

近年来,有机-无机核壳材料因其具有可调的光、电、磁等特性而备受关注．无机物外壳可以增强粒子的热力学稳定性、机械强度和抗拉性能．高分子乳胶粒内核具有弹性,且易成膜,外部包覆无机物的乳胶粒可结合两者特性并产生协同效应．     

Correcting for a density distribution: particle size analysis of core-shell nanocomposite particles using disk centrifuge photosedimentometry

Many types of colloidal particles possess a core-shell morphology. In this Article, we show that, if the core and shell densities differ, this morphology leads to an inherent density distribution for particles of finite polydispersity. If the shell is denser than the core, this density distribution implies an artificial narrowing of the particle size distribution as determined by disk centrifuge photosedimentometry (DCP). In the specific case of polystyrene/silica nanocomposite particles, which consist of a polystyrene core coated with a monolayer shell of silica nanoparticles, we demonstrate that the particle density distribution can be determined by analytical ultracentrifugation and introduce a mathematical method to account for this density distribution by reanalyzing the raw DCP data. Using the mean silica packing density calculated from small-angle X-ray scattering, the real particle density can be calculated for each data point. The corrected DCP particle size distribution is both broader and more consistent with particle size distributions reported for the same polystyrene/silica nanocomposite sample using other sizing techniques, such as electron microscopy, laser light diffraction, and dynamic light scattering. Artifactual narrowing of the size distribution is also likely to occur for many other polymer/inorganic nanocomposite particles comprising a low-density core of variable dimensions coated with a high-density shell of constant thickness, or for core-shell latexes where the shell is continuous rather than particulate in nature.