Polymer Latex Particles Research Articles

Dissolution and Swelling Behaviors of Random and Cross-Linked Methacrylic Acid−Ethyl Acrylate Copolymers

The neutralization behaviors of random and cross-linked methacrylic acid-ethyl acrylate (MAA-EA) copolymers were examined as a function of degree of neutralization (alpha) using potentiometric titration and laser light scattering techniques. The random MAA-EA copolymers exhibit a conformational transition from a compact latex particle to a swollen randomly coiled aggregate upon neutralization over a certain range of alpha. With further addition of NaOH, the swollen aggregates dissociate into several smaller clusters. This conformational change is controlled by the balance between electrostatic repulsion within ionized MAA groups and hydrophobic attraction of EA. The cross-linked MAA-EA copolymers do not undergo a drastic conformational change during neutralization. The polymer latex particles swell slightly upon neutralization, and the extent of chain expansion is proportional to MAA molar composition and inversely proportional to cross-linked density. The electrostatic Gibbs energy (DeltaG(el)) obtained from the potentiometric titration data indicates that a higher MAA portion is favorable for the deprotonization of both the random and cross-linked MAA-EA copolymers, suggesting that the dissociation is mainly dominated by polymer structure instead of the electrostatic attraction between H(+) and -COO(-). Moreover, static and dynamic light scattering results confirmed that the cross-linked latex particle exists as monodispersed hard sphere in the collapsed state, whereas in its swollen state the latex particle possesses a core-shell structure.

Preparation and clinical application of immunomagnetic latex

AbstractMagnetic poly(methyl methacrylate) (PMMA)/poly(methyl methacrylate‐co‐methacrylic acid) [P(MMA–MAA)] composite polymer latices were synthesized by two‐stage soapless emulsion polymerization in the presence of magnetite (Fe3O4) ferrofluids. Different types and concentrations of fatty acids were reacted with the Fe3O4 particles, which were prepared by the coprecipitation of Fe(II) and Fe(III) salts to obtain stable Fe3O4 ferrofluids. The Fe3O4/polymer particles were monodisperse, and the composite polymer particle size was approximately 100 nm. The morphology of the magnetic composite polymer latex particles was a core–shell structure. The core was PMMA encapsulating Fe3O4 particles, and the shell was the P(MMA–MAA) copolymer. The carboxylic acid functional groups (COOH) of methacrylic acid (MAA) were mostly distributed on the surface of the composite polymer latex particles. Antibodies (anti‐human immunoglobulin G) were then chemically bound with COOH groups onto the surface of the magnetic core–shell composite latices through the medium of carbodiimide to form the antibody‐coated magnetic latices (magnetic immunolatices). The MAA shell composition of the composite latex could be adjusted to control the number of COOH groups and thus the number of antibody molecules on the magnetic composite latex particles. With a magnetic sorting device, the magnetic immunolatices derived from the magnetic PMMA/P(MMA–MAA) core–shell composite polymer latex performed well in cell‐separation experiments based on the antigen–antibody reaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1342–1356, 2005

Rapid Gel-Like Latex Film Formation through Controlled Ionic Coacervation of Latex Polymer Particles Containing Strong Cationic and Protonated Weak Acid Functionalities

We introduce a controlled ionic coacervation (CIC) process that rapidly forms uniform, gel-like latex films with significant mechanical integrity without loss of water from the film. This process uses latex particles that contain both strong cationic charges and weak protonated acid groups. An increase in pH ionizes the weak acid and triggers the rapid setting of the latex films. The necessary increase in pH can be achieved by coating the latex onto an alkaline surface (such as concrete) or by controlled release of a fugitive acid (such as carbon dioxide). We explore the effect of latex composition and concentration on this process. We show that the CIC process does not require a water-soluble polymer to obtain the rapid-set film properties. Our proposed mechanism for CIC process is consistent with models for rapid, irreversible, particle-particle aggregation.

Synthesis and properties of soap-free poly(methyl methacrylate-ethyl acrylate-methacrylic acid) latex particles prepared by seeded emulsion polymerization

In order to obtain functional polymer latex particles with clean surface and with surface carboxyl groups, P(MMA-EA) seed particles with the diameter of 335 nm were first synthesized via soap-free batch emulsion polymerization of methyl methacrylate (MMA) and ethyl acrylate (EA), and then the seeded emulsion copolymerization of MMA, EA and MAA (methacrylic acid) onto the seed particles were performed in the absence of emulsifier. Influences of ingredients and conditions on polymerization, latex particle size ( D p ) and its distribution were investigated. Results showed that most of the monomers polymerized onto the seed latex particles in the second step of polymerization by using drop-wise addition method, and D p increased from 483 nm to 829 nm with the mass ratio of core/shell monomers [C]/[S] decreased from 1:2 to 1:15. It was found that D p decreased with the increase of MAA and initiator amounts, and the size of the latex particles became uniform with the decrease of MAA amount and with the increase of [C]/[S] value.

Latex-Coated Polymeric Monolithic Ion-Exchange Stationary Phases. 1. Anion-Exchange Capillary Electrochromatography and In-Line Sample Preconcentration in Capillary Electrophoresis

A sulfonated methacrylate monolithic polymer has been synthesized inside fused-silica capillaries of diameters 50-533-microm i.d. and coated with 65-nm-diameter fully functionalized quaternary ammonium latex particles (AS18, Dionex Corp.) to form an anion-exchange stationary phase. This stationary phase was used for ion-exchange capillary electrochromatography of inorganic anions in a 75-microm-i.d. capillary with Tris/perchlorate electrolyte and direct UV detection at 195 nm. Seven inorganic anions (bromide, nitrate, iodide, iodate, bromate, thiocyanate, chromate) could be separated over a period of 90 s, and the elution order indicated that both ion exchange and electrophoresis contributed to the separation mechanism. Separation efficiencies of up to 1.66 x 10(5) plates m(-1) were achieved, and the monoliths were stable under pressures of up to 62 MPa. Another latex-coated monolith in a 250-microm-i.d. capillary was used for in-line preconcentration by coupling it to a separation capillary in which the EOF had been reversed using a coating of either a cationic polymer or cationic latex particles. Several capillary volumes of sample were loaded onto the preconcentration monolith, and the analytes (inorganic anions) were then eluted from the monolith with a transient isotachophoretic gradient before being separated by electrophoresis in the separation capillary. Linear calibration curves were obtained for aqueous mixtures of bromide, nitrite, nitrate, and iodide. Recoveries of all analytes except iodide were reduced significantly when the sample matrix contained high levels of chloride. The preconcentration method was applied to the determination of iodide in open ocean water and provided a limit of detection of 75 pM (9.5 ng/L) calculated at a signal-to-noise ratio of 3. The relative standard deviation for migration time and peak area for iodide were 1.1 and 2.7%, respectively (n = 6). Iodide was eluted as an efficient peak, yielding a separation efficiency of 5.13 x 10(7) plates m(-1). This focusing was reproducible for repeated analyses of seawater.

Direct and Reverse ATRP of MMA in Aqueous Dispersed Medium in the Presence of a Bipyridine‐Functionalized Block Copolymer Support

AbstractSummary: In a recent communication (Macromol. Rapid Commun. 2002, 23, 871), we reported the synthesis of a bipyridine containing amphiphilic polymer and its usage as macroligand in the atom transfer radical polymerization (ATRP) of MMA in aqueous dispersed medium. Investigations on the mechanism and locus of nucleation by transmission electron microscopy (TEM) studies herein of latex particles prepared by direct ATRP using oil‐soluble ethyl 2‐bromoisobutyrate as initiator revealed a broad particle size distribution between 250 nm and 1 μm, suggesting two nucleation sites, micelles and monomer droplets. By using the water‐soluble initiator 2,2′‐azoisobutyramidine‐dihydrochloride (V‐50) reverse ATRP experiments were conducted at 90 °C. Kinetic measurements showed a sigmoidal slope of monomer conversion versus time as a first indication for an emulsion‐like process. Controlled polymerization behavior was achieved at a ratio of radicals versus Cu(II) deactivator of 1:8. TEM measurements of polymer latex particles obtained by reverse ATRP revealed particle sizes between 100 and 400 nm. Residual copper content of eight PMMA samples prepared by direct and reverse ATRP was determined to be 0.01–0.03 wt.‐% (theoretical 0.73 wt.‐%) and indicated that on average 96–99% of all copper used in a polymerization experiment can be removed from the polymer latex particles by a simple precipitation/washing step.Direct and reverse ATRP experiments of MMA in aqueous media in the presence of an amphiphilic, water‐soluble block copolymer with pendent bipyridine units.magnified imageDirect and reverse ATRP experiments of MMA in aqueous media in the presence of an amphiphilic, water‐soluble block copolymer with pendent bipyridine units.

In situ Structural Characterization of Semi‐Crystalline Polymer Latex Particles by Small‐Angle X‐Ray Scattering

AbstractSummary: The inner structure of polyurethane latex particles has been studied in situ using small‐angle X‐ray scattering (SAXS). From contrast variation SAXS measurements evidence could be given that the dispersed particles are semi‐crystalline. The semi‐crystalline structure gives a strong contribution to the measured intensities in an intermediate range of scattering vectors. This contribution, which is independent of the adjusted contrast, could be separated and the long period of the lamellar structure could thus be determined quantitatively to 11 nm. In addition, it was found that the particles exhibit a core‐shell structure which arises from electron‐rich acid groups that are preferentially located at the particle surface.Transmission electron microscopy (TEM) picture of the PUR particles.imageTransmission electron microscopy (TEM) picture of the PUR particles.

The effect of first-stage polymer Tg on the morphology and thermomechanical properties of structured polymer latex particles

A series of heterogeneous latexes having stage ratios of 40:60 between the first and second stage polymers were prepared by emulsion polymerization. The first-stage polymers were non-polar S-BuA with T gs ranging from + 100 °C to + 20 °C and the second stage polymer was polar MMA–BuA–MAA having a T g of 20 °C. The latex particle morphologies were studied using TEM and the thermomechanical properties of the resulting latex films were studied with DSC and DMA. Calculated diffusion rates for propagating species during the reactions were correlated to the observed morphologies and to the amount of interphase in the latex particles. To cite this article: O.J. Karlsson et al., C. R. Chimie 6 (2003).

Diffusion barriers of tripartite sporopollenin microcapsules prepared from pine pollen.

Tripartite sporopollenin microcapsules prepared from pine pollen (Pinus sylvestris L. and Pinus nigra Arnold) were analysed with respect to the permeability of the different strata of the exine which surround the gametophyte and form the sacci. The sexine at the surface of the sacci is highly permeable for polymer molecules and latex particles with a diameter of up to 200 nm, whereas the nexine covering the gametophyte is impermeable for dextran molecules, with a Stokes' radius > or =4 nm (Dextran T 70), and for the tetravalent anionic dye Evans Blue (Stokes' radius = 1.3 nm). The central capsules obtained by dissolution of the sporoplasts showed strictly membrane-controlled exchange of non-electrolytes, with half-equilibration times in the range of minutes (monosaccharides, oligosaccharides) to hours (dextran molecules with Stokes' radii up to 2.5 nm). The dependence of the permeability coefficients of the nexine for non-electrolytes on Stokes' radius or molecular weight shows that the aqueous pores through the nexine are inhomogeneous with respect to their size, and that most pores are too narrow for free diffusion of sugar molecules. To explain the barrier function of the nexine for Evans Blue, it is assumed that at least the larger pores, which enable slow permeation of dextran molecules, contain negative charges.

Charge and salt-driven reentrant order–disorder and gas–solid transitions in charged colloids

Monte Carlo simulations have been performed for aqueous charged colloidal suspensions as a function of effective charge density ( σ) on the particles and salt concentration C s . We vary the effective charge density in our simulations over a range where a reentrant solid–liquid transition in suspensions of silica and polymer latex particles has been reported by Yamanaka et al. (Phys. Rev. Lett. 80 (1998) 5806). We show that at low ionic strengths a homogeneous liquid-like ordered suspension undergoes crystallization upon increasing σ. Further increase in σ resulted once again in a disordered state, which is in agreement with experimental observations. In addition to this reentrant order–disorder transition, we observe an inhomogeneous-to-homogeneous transition in our simulations when salt is added to the disordered inhomogeneous state. This inhomogeneous-to-homogeneous disordered transition is analogous to the solid–gas transition of atomic systems and has not yet been observed in charged colloids. The reported experimental observations on charged colloidal suspensions are discussed in the light of present simulation results.

Nanoscopic Polymer Particles with a Well‐Defined Surface: Synthesis, Characterization, and Properties

AbstractWe review our recent work on polymeric latex particles having a well‐defined surface of grafted polymers. Two types of particles are discussed: i) particles with a thermosensitive shell, and ii) particles bearing a dense layer of linear polyelectrolyte chains on their surface (“spherical polyelectrolyte brush”). Both types of particles consist of a polystyrene core onto which either linear or crosslinked chains are grafted. The synthesis of these core–shell particles proceeds in a two‐step process which is reviewed in detail. In particular, we discuss the photo‐emulsion polymerization used for the synthesis of the spherical polyelectrolyte brushes. Most of the studies of these particles have been done in aqueous suspension. Here the equilibrium structure of the surface layer of the particles has been investigated by dynamic light scattering and by small‐angle X‐ray scattering. Results deduced from the flow behavior of the particles in dilute solution can directly be derived from static data. Very recent data refer to the interaction of the spherical polyelectrolyte brushes with solid interfaces. It is demonstrated that particles bearing positively charged polyelectrolyte chains interact strongly with negatively charged surfaces. The strong interaction that is directly evident from AFM studies can be used to generate 2D networks of the particles on the surface. Schematic representation of the synthesis of defined spherical polyelectrolyte brushes.magnified imageSchematic representation of the synthesis of defined spherical polyelectrolyte brushes.

Synthesis of well‐defined, functionalized polymer latex particles through semicontinuous emulsion polymerization processes

AbstractThe design of a semicontinuous emulsion polymerization process, primarily based on theoretical calculations, has been carried out with the objective of achieving overall independent control over the latex particle size, the monodispersity in the particle size distribution, the homogeneous copolymer composition, the concentration of functional groups (e.g., carboxyl groups), and the glass‐transition temperature with n‐butyl methacrylate/n‐butyl acrylate/methacrylic acid as a model system. The surfactant coverage on the latex particles is very important for maintaining a constant particle number throughout the feed process, and this results in the formation of monodisperse latex particles. A model has been set up to calculate the surfactant coverage from the monomer feed rate, surfactant feed rate, desired solid content, and particle size. This model also leads to an equation correlating the polymerization rate to the instantaneous conversion of the monomer or comonomer mixture. This equation can be used to determine the maximum polymerization rate, only below or at which monomer‐starved conditions can be achieved. The maximum polymerization rate provides guidance for selecting the monomer feed rate in the semicontinuous emulsion polymerization process. The glass‐transition temperature of the resulting carboxylated poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) copolymer can be adjusted through variations in the compositions of the copolymers with the linear Pochan equation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 30–41, 2003

Sonochemical production of fluorescent and phosphorescent latex particles.

A novel method for producing nanosized polymer latex particles doped with fluorescent and phosphorescent solutes is described. Methyl methacrylate monomer (10 wt %) containing either pyrene, 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DMDP), or 1-bromonaphthalene was ultrasonically dispersed in water and simultaneously polymerized to produce approximately 60 nm diameter latex particles. A fluorescence spectroscopic examination of the latex dispersion containing either pyrene or DMDP showed that the solutes were not covalently bound to the polymer and that they were embedded in a highly viscous environment possessing a low polarity (dielectric constant on the order of 2). The fluorescence lifetime of the pyrene in the core of the poly(MMA) latex was found to be 520 ns, irrespective of the oxygen concentration in the dispersion. Room-temperature phosphorescence was observed from 1-bromonaphthalene, with a lifetime of 2.0 ms in an argon atmosphere. In the presence of air, phosphorescence was still observable although with a partially reduced emission intensity.

Polymer electrostatics: detection and speciation of trapped electric charges by electric probe and analytical electron microscopy

AbstractThis work reviews new probe and electron microscopy approaches for the detection of charged domains in insulating polymers, as well as for the identification of the charge‐bearing species: scanning electric potential microscopy (SEPM), electric force microscopy (EFM) and energy‐loss spectroscopy imaging in the transmission electron microscope (ESI‐TEM). The SEPM and EFM micrographs show patterned domains bearing excess electric charges and extending for tens of nanometers, in polymer latex particles and films. The charged species are identified by ESI‐TEM as emulsion polymerization initiator and surfactant residues, as well as the associated counter‐ions. Charged domains are also observed in common thermoplastic polymers, producing unexpectedly large electric potential gradients.

Residual order in amorphous dry films of polymer latices: indications of an influence of particle interaction

We report small angle X-ray scattering and atomic force microscopy measurements on macroscopically thick, dry films of polymer latex particles. While the surface of dried droplets has long range order due to layering effects, the overall bulk structure is amorphous. This holds for both low charge polymethylmetacrylate particles and for highly charged polystyrene particles with additional stabilisation with sodiumdodecylsurfate. In the latter case, however, considerable amounts of residual crystal-like order is observed.

Polymer/silica nanoscale hybrids through sol–gel method involving emulsion polymers. I. Morphology of poly(butyl methacrylate)/SiO2

AbstractIn this article, we report on an approach of using an emulsion polymerized polymer in preparing organic–inorganic nanocomposites through a sol–gel technique. By mixing a polymer emulsion with prehydrolyzed tetraethoxysilane transparent poly(butyl methacrylate)/SiO2, nanocomposites were prepared as shown by TEM. AFM, FTIR, and XPS results show that there is a strong interaction between polymer latex particles and the SiO2 network. Comparison of the emulsion method with a traditional solution method shows that nanocomposites can be prepared by both methods, but there is some difference in their morphology and properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 446–454, 2002

Quantitative determination of large structures by small-angle light scattering

A new small-angle light scattering camera has been developed. In contrast to conventional detection the present system is based on a recently developed two-dimensional charge-coupled-device chip made by Thomson (France). The advantage of this chip is its excellent linear response and very low dark signal even at room temperature. The best linearity was obtained by leading each pixel signal through the same amplifying system. The optical system covered a diffraction angular region from about 1° to 15° (q = 0.2–2.6 μm−1). The camera was calibrated with grids and pinholes and was tested with polymer latex particles in solution and with spherulites from polymer films.

Atomic force microscope studies of stainless steel: Surface morphology and colloidal particle adhesion

An atomic force microscope has been used to image four commercial stainless steel samples of widely differing surface finishes. Analysis of the images allowed quantification of surface roughness over different area scales, 50 × 50 μm, 10 × 10 μm and 1 × 1 μm. The atomic force microscope was also used to measure directly the adhesion of a single polymer latex particle (radius ∼5 μm) to the surface in solution using the colloid probe technique. It was found that the adhesion increased with decreasing roughness, except for the smoothest surface which exhibited very regular surface features on the area scale most relevant to adhesion of the particle (1 × 1 μm). There was a good correlation between the variability of adhesion over each surface and the corresponding variability in surface roughness. Measurements of this type should prove useful in the technical/economic choice of surface finish for a particular purpose. As the colloid probe has dimensions comparable to those of bacteria and yeast cells, such measurements should especially be of value in the selection of surface finish likely to minimise bioadhesion.

Mobility of SDOSS Powered by Ionic Interactions in Sty/n-BA/MAA Core−Shell Latex Films. 21. A Spectroscopic Study

While molecular level interactions between sulfonate groups of sodium dioctylsulfosuccinate (SDOSS) and COOH groups in styrene/n-butyl acrylate/methacrylate acid (Sty/n-BA/MAA) copolymer particles have been the subject of our earlier studies, the main focus of this work is to establish how MAA groups affixed to polymer latex particle surfaces will affect SDOSS mobility in Sty/n-BA/MAA latex films. The ultimate objective is to develop a series of model systems simulating the degree of neutralization of polymer surfaces and how it may alter polymer contractions and release of entropically attached molecules to interfacial regions. These studies show that the release of SDOSS molecules from MAA containing Sty/n-BA particles is attributed to two factors: (1) entropic effect due to increased compatibility resulting from surfactant penetration into latex particle surfaces and (2) enhanced particle out-layer glass transition temperature (Tg). The SDOSS release is inhibited when surface neutralization levels are...

Brownian Dynamics Simulation of Film Formation of Mixed Polymer Latex in the Water Evaporation Stage

Brownian dynamics simulations of the filming process of a mixed polymer latex in the water evaporation stage were performed in order to explore the effect of surface potential on latex particle packing and distribution at a temperature far below the glass transitions of polymers in bulk. Polymer latex particles are modeled as spheres that interact via DLVO potential with various surface charge densities for emulsifier-free emulsion polymerized particles and dispersion polymerized particles. It is found that the distribution of modeled poly(methyl methacrylate) and polystyrene latex particles in the finally formed film exhibits a noticeable dependence of surface potentials of latex particles. When the difference of the surface potentials between binary mixed latex particles is small, the particles distribute randomly. In contrast, when the difference of the surface potentials between binary mixed latex particles is large, heterocoagulation occurs and the polymer latex in which the repulsive electrostatic potential is weak will form clusters in the film. The results are in agreement with laser confocal fluorescence microscopy observations of fluorescent dye labeled poly(methyl methacrylate) and polystyrene mixed latex films. The correlation between latex particles increases with increasing repulsive electrostatic potential, and the spatial order can be obtained at the end of the water evaporation stage.