Crosslinked Polystyrene Particles Research Articles

Synthesis of non-spherical polymer particles using the activated swelling method

The preparation of particles with non-spherical shapes is a challenging endeavor, often requiring a significant ingenuity, complex experimental procedures and difficulties to obtain reproducible results. In this work we prove that monodisperse non-spherical polymer particles possessing asymmetric Janus structure can be easily produced by using an activated swelling method in combination with a control of the rate of free radical polymerization through the addition of the inhibitors 4-methoxyphenol (MEHQ) and O2. Monodisperse non cross-linked polystyrene particles, used as seeds, are activated by the addition of an initiator, which promotes their swelling ability, and then swollen with a monomers mixture (methyl methacrylate, glycidyl methacrylate and ethylene glycol dimethacrylate), before being polymerized in presence of both MEHQ and O2. Our results show that only when both MEHQ and O2 are present during the course of the polymerization, the particles shape can be controlled, from spherical to asymmetrical. A variety of particles shapes can be obtained, ranging from dimpled spheres, flattened spheres and Janus particles by varying the swelling ratio, always with excellent monodispersity and reproducibility. Finally, to provide even more complex functionalities to these non-spherical polymer particles, iron oxide nanocrystals were grown within the polymer matrix resulting in superparamagnetic particles.

Patchy Colloidal Clusters with Broken Symmetry.

Colloidal clusters are prepared by assembling positively charged cross-linked polystyrene (PS) particles onto negatively charged liquid cores of swollen polymer particles. PS particles at the interface of the liquid core are closely packed around the core due to interfacial wetting. Then, by evaporating solvent in the liquid cores, polymers in the cores are solidified and the clusters are cemented. As the swelling ratio of PS cores increases, cores at the center of colloidal clusters are exposed, forming patchy colloidal clusters. Finally, by density gradient centrifugation, high-purity symmetric colloidal clusters are obtained. When silica-PS core-shell particles are swollen and serve as the liquid cores, hybrid colloidal clusters are obtained in which each silica nanoparticle is relocated to the liquid core interface during the swelling-deswelling process breaking symmetry in colloidal clusters as the silica nanoparticle in the core is comparable in size with the PS particle in the shell. The configuration of colloidal clusters is determined once the number of particles around the liquid core is given, which depends on the size ratio of the liquid core and shell particle. Since hybrid clusters are heavier than PS particles, they can be purified using centrifugation.

One-pot synthesis of cross-linked nonspherical polystyrene particles via dispersion polymerization: the effect of polymerization conditions on the morphology of the particles

Herein we report the fabrication of cross-linked polystyrene particle with a variety of nonspherical morphologies such as red blood cell-like, cap-like, apple-like and so forth through two-stage dispersion polymerization in polar media. Furthermore, we examine the effect of different polymerization conditions including monomer and cross-linker concentration, and the type of initiator, monomer, stabilizer and cross-linker on the shape of the obtained particles. The acquired results reveal that the particles morphology can be altered from spherical to nonspherical with a decrease in the content of cross-linker and monomer, and using more reactive initiators and cross-linkers. Furthermore, particles shape can be changed through the addition of a different second-stage monomer type. Finally, the possible formation mechanism of the discussed nonspherical particles is illustrated.

Pt Nanoparticles-Macroporous Carbon Nanofiber Free-Standing Cathode for High-Performance Li-O2 Batteries

Controlling the pore structure of cathodes has a decisive effect on the performance of lithium (Li)-O2 batteries. In this work, macroporous carbon nanofiber (MCNF) decorated with Pt nanoparticles (PtNPs) (PtNP-MCNF) are successfully fabricated. Their electrochemical performance as cathodes for a Li-O2 battery is evaluated. The MCNF mats are fabricated through an electrospinning and templating method using cross-linked polystyrene particles. PtNPs are grown on the surface of the MCNF through a solvothermal reaction. As-prepared PtNP-MCNF has interconnected macropores along the MCNF interior and abundant surface openings. These macropores are also connected to larger pores between individual MCNFs through the orifices on the MCNF surface, rendering a hierarchical porous structure. Owing to the highly porous structure and catalytic activity of PtNPs, Li-O2 cells using PtNP-MCNF cathodes exhibit considerably improved performance. In particular, with regard to cycle stability, the Li-O2 cell using PtNP-MCNF attains over 470 cycles in total while discharging at a capacity of 1000 mAh gc−1 with a current density of 500 mA gc−1. Such a high performance of the Li-O2 cell can be attributed to a facilitated Li+ and O2 transportation through the highly porous structure, and highly reversible Li-O2 operation over its life-cycle by means of catalytic activity of PtNPs.

Pt Nanorods-Decorated Macroporous Carbon Nanofiber Free-Standing Cathodes for High-Performance Li-O2 Battery

Controlling the pore structure of cathodes has a strong influence on the performance of Li-O2 battery. In the present study, macroporous carbon nanofiber (MCNF) mats are successfully fabricated through an electrospinning and templating methods using cross-linked polystyrene particles. Additionally, Pt nanorods are grown on the surface of the MCNF (PtNR-MCNF) as catalysts for Li/O2 reactions. As-prepared PtNR-MCNF has interconnected macropores along the MCNF interior and abundant surface openings. Those macropores are also connected to larger pores between individual MCNF through the orifices on the MCNF surface, rendering a hierarchical porous structure. Owing to the highly porous structure, Li-O2 cells using the PtNR-MCNF cathodes achieved a specific capacity of approximately 7,000 mAh/gc and even more at a current density of 200 mA/gc. In particular, the Li-O2 cell using the PtNR-MCNF cathode exhibited higher electrochemical performance in terms of rate capability, energy efficiency, and cycle stability. This study demonstrates that the growth of PtNRs resulted in the formation of poorly crystalized Li2O2, which significantly reduced the overpotentials, both during the discharge and the charge. Additionally, it contributed to the considerably prolonged cycle life of the Li-O2 cell using the PtNR-MCNF (468 cycles) compared to the cell using the MCNF cathode (272 cycles) with a limiting capacity of 1,000 mAh/gc at a current density of 500 mA/gc.

Size control of cross-linked carboxy-functionalized polystyrene particles: Four orders of magnitude of dimensional versatility

Synthesis of functionalized organic particles is an expanding area of exploration due to versatile potential applications including imaging agents, drug delivery vehicles, and supported synthesis. A robust, customizable method that allows modification of size, degree of cross–linking, identity of the crosslinker, and desired functionality, while retaining particle integrity would be highly advantageous. Here, we report the straightforward, versatile syntheses of cross-linked carboxy polystyrene (PS) particles ranging from 50 nm to 500 µm in diameter that retain their morphology in organic solvents. Removal of a protecting group exposed free benzoic acid groups that were readily functionalized to afford peroxide, ester, or amide moieties. The identity and density of the crosslinker were also systematically modified to alter the swelling properties of the microparticles. The particles were rigorously characterized by IR and 13C NMR spectroscopy, SEM, and optical imaging. The methods reported here provide a robust and reliable way to systematically and reproducibly synthesize functionalized cross-linked PS-based particles spanning a wide range of sizes.

Janus Particles Synthesis by Emulsion Interfacial Polymerization: Polystyrene as Seed or Beyond?

New strategies for synthesis of Janus particles are of essential importance in the advancement of material science and technology. However, it remains a great challenge to synthesize uniform Janus particles with controllable topological and chemical anisotropy. To overcome this challenge, we have recently developed a general emulsion interfacial polymerization approach. This approach can be applicable to a wide variety of vinyl monomers, including positively charged, neutrally charged, and negatively charged monomers. Different from the traditional seed swelling emulsion polymerization that usually involved using cross-linked polystyrene (PS) particles as seeds to produce Janus particles, we preloaded non-cross-linked PS particles in the emulsion system to construct an interfacial polymerization system. However, the role of these non-cross-linked PS particles in the emulsion interfacial polymerization is unclear. In this work, we revealed the role of non-cross-linked PS particles preloaded in emulsion int...

Rapid production of monodisperse cross-linked red blood corpuscle-like particles via scalable one-pot dispersion polymerization

Cross-linked polystyrene (PS) particles having red blood corpuscle (RBC)-like shape were synthesized by one-pot dispersion polymerization of styrene with ethanol/water mixture and ethylene glycol dimethacrylate (EGDMA) as the reaction medium and cross-linker, respectively. Monitoring of the reaction showed that RBC-like shape forms due to asymmetric shrinkage of a cross-linked network during the phase separation. In addition, three dimensional phase diagram was generated based on the yielded data that showed that the formation of such unique shape extremely depends on the polarity of the medium and injection time of the cross-linker. In situ synthesis of RBC-like particles, as promising biomaterials in targeted drug delivery and a model for the understanding of the cell behavior, via such fast and high solid content approach makes it to be conducive to subsequent scale up, i.e. potential commercial adoption.

On tuning microgel character and softness of cross-linked polystyrene particles.

Polystyrene (PS) microgel colloids have often been used successfully to model hard sphere behaviour even though the term "gel" invokes inevitably the notion of a more or less soft, deformable object. Here we systematically study the effect of reducing the cross-link density from 1 : 10 (1 cross-link per 10 monomers) to 1 : 100 on particle interactions and "softness". We report on the synthesis and purification of 1 : 10, 1 : 25, 1 : 50, 1 : 75 and 1 : 100 cross-linked PS particles and their characterization in terms of single particle properties, as well as the behaviour of concentrated dispersions. We are able to tune particle softness in the range between soft PNiPAM-microgels and hard PMMA particles while still allowing the mapping of the microgels onto hard sphere behavior with respect to phase diagram and static structure factors. This is mainly due to a rather homogeneous radial distribution of cross-links in contrast to PNiPAM microgels where the cross-link density decreases radially. We find that up to a cross-link density of 1 : 50 particle form factors are perfectly described by a homogeneous sphere model whereas 1 : 75 and 1 : 100 cross-linked spheres are slightly better described as fuzzy spheres. However the fuzziness is rather small compared to typical PNiPAM microgels so that a hard sphere mapping still holds even for these low cross-link densities. Finally, by varying the reaction conditions - changing from batch to semibatch emulsion polymerization and varying the feed rate or by adjusting the monomer to initiator ratio we can tune the fuzziness or significantly alter the inner structure to a more open, star-like architecture.

Preparation and Surface Property of Fluoroalkyl End-Capped Vinyltrimethoxysilane Oligomer/Talc Composite-Encapsulated Organic Compounds: Application for the Separation of Oil and Water

Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [R(F)-(CH2-CHSi(OMe)3)n-R(F); n = 2, 3; R(F) = CF(CF3)OC3F7 (R(F)-VM oligomer)] can undergo the sol-gel reaction in the presence of talc particles under alkaline conditions at room temperature to provide the corresponding fluorinated oligomeric silica/talc nanocomposites (RF-VM-SiO2/Talc). A variety of guest molecules such as 2-hydroxy-4-methoxybenzophenone (HMB), bisphenol A (BPA), bisphenol AF, 3-(hydroxysilyl)-1-propanesulfonic acid (THSP), and perfluoro-2-methyl-3-oxahexanoic acid (R(F)-COOH) are effectively encapsulated into the R(F)-VM-SiO2/Talc composite cores to afford the corresponding fluorinated nanocomposites-encapsulated these guest molecules. The R(F)-VM-SiO2/Talc composites encapsulated low molecular weight aromatic compounds such as HMB and BPA can exhibit a superoleophilic-superhydrophobic characteristic on the surfaces; however, the R(F)-VM-SiO2/Talc composite-encapsulated THSP and R(F)-COOH exhibit a superoleophobic-superhydrophilic characteristic on the modified surfaces. In these nanocomposites, the R(F)-VM-SiO2/Talc/THSP composites are applicable to the surface modification of polyester fabric, and the modified polyester fabric possessing a superoleophobic-superhydrophilic characteristic on the surface can be used for the membrane for oil (dodecane)/water separation. In addition, the R(F)-VM-SiO2/Talc composites-encapsulated micrometer-size controlled cross-linked polystyrene particles can be also prepared under similar conditions, and the obtained composite white-colored particle powders are applied to the packing material for the column chromatography to separate water-in-oil (W/O) emulsion.

Efficient synthesis of asymmetric particles by sol-gel process

This paper presents a novel and facile method of synthesizing polymer/silica particles with controlled asymmetric morphologies. Our approach is based on the sol–gel process in which cross-linked polystyrene particles (CPS) are adopted as templates and 3-mercaptopropyltriethoxysilane is used as a single silica source. The reaction process causes silane oligomer to preferentially grow on the local surface of CPS, giving rise to polystyrene/thiol-functionalized silica composite particles with a tunable shape. It is found that the morphologies of particles can be easily tailored by changing the ratio of ethanol/water in the reaction medium. In addition, the amount of cross-linker used during the polymerization also plays a key role in the formation of various complex-shaped particles. Controlled geometries of these organic/inorganic composite particles will allow a broad range of potential applications, such as photonic crystals, Pickering emulsifier, sensors, and so on.

Redox-Responsive Polymer Brushes Grafted from Polystyrene Nanoparticles by Means of Surface Initiated Atom Transfer Radical Polymerization

Well-defined poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate) (PFcMA) brushes were synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) on cross-linked polystyrene particles. The ATRP of FcMA monomer was reinvestigated leading to molar masses up to 130 kg mol–1 with a good reaction control and high monomer conversion (91%). The SI-ATRP was done with different amounts of initiator in the PS particle shell leading to PFcMA surface conformations from “mushroom-like” to dense “brush-like” polymers, which could be confirmed by dynamic light scattering (DLS) experiments. Redox-responsive behavior of the PFcMA shell was investigated by DLS and cyclic voltammetry (CV) measurements indicating a tremendous increase in the hydrodynamic volume of the ferrocene-containing shell. The transformation of PFcMA-grafted PS particles to magnetic iron oxides after thermal treatment could be investigated by SQUID magnetization measurements showing the typical hysteresis for ferromagnetic material.

Polymer induced changes of the crystallization scenario in suspensions of hard sphere like microgel particles

We investigated the crystallization scenario of highly cross linked polystyrene particles dispersed in the good solvent 2-ethylnaphtalene and their mixtures with non-adsorbing low molecular weight polysterene polymer using time resolved static light scattering. The samples were prepared slightly below the melting volume fraction of the polymer free system. For the polymer free samples, we obtained polycrystalline solids via crystallization scenario known from hard sphere suspensions with little competition of wall crystal formation. Addition of non-adsorbing low molecular weight polystyrene polymer leads to a considerably slowing down of the bulk crystallization kinetics. We observed a delay of the precursor to crystal conversion for the bulk crystallization while the induction times for the wall nucleation are reduced. The increased polymer concentration thus shifts the balance between the two competing crystallization pathways giving the possibility to tune the relative amount of wall based crystals.

Microporous Polystyrene Particles for Selective Carbon Dioxide Capture

This study presents the synthesis of microporous polystyrene particles and the potential use of these materials in CO(2) capture for biogas purification. Highly cross-linked polystyrene particles are synthesized by the emulsion copolymerization of styrene (St) and divinylbenzene (DVB) in water. The cross-link density of the polymer is varied by altering the St/DVB molar ratio. The size and the morphology of the particles are characterized by scanning and transmission electron microscopy. Following supercritical point drying with carbon dioxide or lyophilization from benzene, the polystyrene nanoparticles exhibit a significant surface area and permanent microporosity. The dried particles comprising 35 mol % St and 65 mol % DVB possess the largest surface area, ∼205 m(2)/g measured by Brunauer-Emmett-Teller and ∼185 m(2)/g measured by the Dubinin-Radushkevich method, and a total pore volume of 1.10 cm(3)/g. Low pressure measurements suggest that the microporous polystyrene particles exhibit a good separation performance of CO(2) over CH(4), with separation factors in the range of ∼7-13 (268 K, CO(2)/CH(4) = 5/95 gas mixture), which renders them attractive candidates for use in gas separation processes.

Facile method to prepare monodisperse polystyrene particles by hydrothermal process

A facile method to prepare monodisperse polystyrene (PS)/cross-linked PS particles was studied by combining hydrothermal process with dispersion polymerisation. Compared to traditional dispersion polymerisation, in this way the polymerisation of styrene in ethanol–water media could be carried out in a relatively wide ethanol/water ratio range from 10/90 to 70/30, consequently monodisperse particles from 160 to 1300 nm in size were generated at 80°C. It implies that the monodisperse PS particles could be acquired simply and the significant change in PS particle size could be adjusted by only varying the ethanol/water ratio. The phenomenon could be inferred that the hydrothermal process improved the solubility of the monomer in the media under a higher reaction pressure, which enabled this method to expand the ethanol/water ratio range for traditional dispersion polymerisation. Furthermore, the monodisperse cross-linked PS particles could also be obtained even at the cross-linking agent being up to 2% without addition of stabiliser through this method. Not using stabiliser could enlarge the application range of the cross-linked monodisperse PS particles. The formation process of the particles was detected using scanning electron microscopy. The particle morphology transformation along with hydrothermal reaction in the early stage was demonstrated, that is, the initial irregular particles in different size congregated gradually to form monodisperse particles.

Tin(IV) Oxide Coatings from Hybrid Organotin/Polymer Nanoparticles

Tin dioxide coatings are widely applied in glasses and ceramics to improve not only optical, but also mechanical properties. In this work, we report a new method to prepare SnO(2) coatings from aqueous dispersions of polymer/organotin hybrid nanoparticles. Various liquid organotin compounds were encapsulated in polymeric nanoparticles synthesized by miniemulsion polymerization. Large amounts of tetrabutyltin and bis(tributyltin) could be successfully incorporated in cross-linked and noncross-linked polystyrene nanoparticles that served as sacrificial templates for the formation of tin oxide coatings after etching with oxygen plasma or calcination. Cross-linked polystyrene particles containing bis(tributyltin)--selected for having a high boiling point--were found to be especially suited for the oxide coating formation. The content of metal in the particles was up to 12 wt %, and estimations by thermogravimetrical indicated that at least 96% of the total organotin compound was converted to SnO(2). The resulting coatings were mainly identified as tetragonal SnO(2) (cassiterite) by X-ray diffraction, although a coexistence of this phase with orthorhombic SnO(2) was observed for samples prepared with bis(tributyltin).

Synthesis of crosslinked polystyrene particles by seeded batch polymerization with monomer absorption

A highly crosslinked, monodispersed polystyrene(PS) particle was prepared by a seeded batch dispersion polymerization with a monomer absorption method. Prior to polymerization, 1.9 μm monodispersed PS seed particles were treated under an optimum condition of monomer absorption. The effects of divinylbenzebe(DVB) concentration and polymerization temperature were examined for styrene(in PS seed)/styrene(in the second stage) mass ratio of 1:1 in the medium range of EtOH/water mass ratio of 100/0-80/20 and 2.3 μm uniform crosslinked PS particles containing 15%-20% (mass fraction) DVB were prepared at 60–70 °C. The results show that monomer absorption before the second stage of polymerization is more effective to prepare highly crosslinked monodispersed PS particles.

Mesoporous polystyrene nanoparticles synthesized by semicontinuous heterophase polymerization

The synthesis by semicontinuous heterophase polymerization and the characterization of mesoporous crosslinked polystyrene particles in the nanometer range (ca. 30 nm) are reported here. The particles have pores between 6 and 8 nm in diameter and pore volume around 0.40 cm3/g. In spite that the polymerization was not carried out at highly monomer-starved conditions, particles with narrow size distribution were obtained, which is ascribed to inter-particle hetero-coagulation at latter stages of polymerization, due to lack of enough surfactant to cover all the particles even before 45% global conversion.

Highly crosslinked micron-sized, monodispersed polystyrene particles by batch dispersion polymerization, Part 1: Batch, delayed addition, and seeded batch processes

The seeded batch dispersion polymerization with or without monomer absorption was compared with the batch polymerization and delayed addition by batch polymerization, to prepare the highly crosslinked, monodispersed polystyrene (PS) particles. The seeded batch polymerization was carried out under the variation of styrene (in second stage)/styrene (in PS seed) (St/St) ratio, divinylbenzene (DVB) concentration, and polymerization temperature using 1.9-μm monodispersed PS seed particles. The experimental results imply that the seeded batch process is more efficient method that could avoid the sensitive particle nucleation step in the presence of the crosslinker than the batch and delayed addition processes. Without monomer absorption, 2.3-μm uniform crosslinked PS particles with 7 wt % of the DVB were prepared in 1/1 (St/St) ratio. In comparison, with the monomer absorption, monodispersed and smooth-surfaced PS particles containing 20 wt % of the DVB were formed. A total of 5% weight loss of the crosslinked PS particles determined by TGA occurred from 353.8 to 374.8°C, and the degree of swellability in toluene decreased from 150 to 104.5% with increasing the DVB concentration from 5 to 20 wt % because of the increase of the crosslink density of the particles. The seeded polymerization, especially through monomer absorption procedure, is a novel way to obtain highly crosslinked, monodispersed PS particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation of Submicron-sized Snowman-like Polystyrene Particles via Radiation-induced Seeded Emulsion Polymerization

Abstract In this paper, we have successfully prepared submicron-sized snowman-like polystyrene (PS) particles by radiation-induced seeded emulsion polymerization at room temperature. The monodispersed crosslinked PS particles with an average size of 358 nm acted as seed particles. The influence of polymer/monomer weight ratio on the morphology was studied. The results showed that snowman-like PS particles could be fabricated in high yield about 90% when the polymer/monomer weight ratio was 0.2:1.