Preparation and characterization of crosslinked PMMA latex particles stabilized by grafted copolymer

 The preparation of polymethyl methacrylate lattices stabilized by polyhydroxystearic acid and crosslinked with ethylene glycol dimethylmethacrylate (EGDM) has been studied. Crosslinking is a new development in the synthesis of PMMA latex. The particles are monodisperse when the concentration of EGDM ranges from 0.33 to 1.44%. The lattices are stable in aromatic and aliphatic solvents. Swelling occurs due to penetration of solvent molecules into the latex. The degree of swelling is calculated by viscosity and by dynamic light scattering measurements. Received: 30 January 1997 Accepted: 2 June 1997     

Colloidal stability of dextran-modified latex particles toward adsorption of concanavalin A

The colloidal stability of the dextran-modified poly(methyl methacrylate) (PMMA) latex particles toward adsorption of a carbohydrate-binding protein, concanavalin A (Con A), is primarily controlled by the charge neutralization mechanism. Formation of a crosslinked network structure via the specific affinity interactions between the dimeric Con A molecules and the dextran molecules anchored onto different latex particles may also have an impact on the coagulation kinetics. Judging from the data of coagulation kinetics, the colloidal stability of the latex particles toward added Con A in the decreasing order is: latex particles without dextran modification>latex particles with a dextran content of 2.15%>latex particles with a dex-tran content of 1.24% based on total polymer weight (PMMA+grafted dextran). The coagulation mechanisms involved in the adsorption of Con A onto the latex particles have been proposed to explain these experimental data. Charge neutralization of the negatively charged latex particles by adsorption of the positively charged Con A is the predominant destabilization mechanism. The ratio of the number of dextran active sites to that of Con A molecules plays an important role in the formation of the crosslinked network structure. The electrolytes in water cause a reduction in the electrostatic repulsion force among the interactive latex particles, but this ionic strength effect is not significant in comparison with charge neutralization. Received: 22 October 1997 Accepted: 24 December 1997     

The synthesis of polymer suspension with narrow particle size distribution for immunochemical investigations

 Heterophase polymerization of styrene in the presence of di-p-tolyl-o-carbalkoxyphenylcarbinol (DTC) soluble in monomer and insoluble in water, as stabilizer, was investigated. The factors affecting polymer particle diameter, their size distribution and stability were investigated. It was suggested that polymer particles are formed from monomer droplets. The polystyrene suspension with narrow particle size distribution synthesized in the presence of DTC, was used for immunochemical research. Received: 10 March 1998 Accepted: 8 June 1998     

Preparation of polystyrene particles with narrow particle size distribution by γ-ray initiated miniemulsion polymerization stabilized by polymeric surfactant

Co-60 γ-ray initiated miniemulsion polymerization of styrene stabilized by an alkali soluble polymeric surfactant (ASPS) was studied in this work. The affecting factors, including absorbed dose, dose rate, surfactant concentration, and hexadecane (HD) concentration, were systematically studied. The particle size and particle size distribution (PSD) of final latexes was determined by transmission electron microscope (TEM). The results indicated that polystyrene (PS) particles with narrow PSD could be easily prepared by this method, and the particle size could be controlled from 50 nm to 250 nm by adjusting the concentration of HD and ASPS. HD concentration, surfactant concentration, dose rate and total absorbed dose strongly affected the particle size and PSD of PS latexes.     

Iron oxyhydroxide colloids stabilized with polysaccharides

 Neutralization of iron salts in aqueous solutions of κ-carrageenan and cellulose sulfate results in iron oxyhydroxide–polysaccharide hybrid colloids with unusual pH stability up to pH 13. It is shown that both polysaccharides form a tight polymer layer surrounding the inorganic particles, which in the case of κ-carrageenan is cross-linked by helical domains forming a self-assembled nanoreactor. The stabilized iron oxyhydroxide particles can undergo further reactions, for example, it is possible by a chemical reaction to produce stabilized magnetite particles. Repetition of the loading/neutralization steps in the reaction results in hybrids with iron contents much higher than the stoichiometric balance of iron and functional groups of the polymer (greater than 100% Fe/SO₄ ⁻). This combination of high iron content with a natural polysaccharide stabilizer makes these colloids interesting for a number of applications, for example, for nutritional purposes or as contrasting agents for tomography. Received: 7 September 1999 Accepted in revised form: 6 December 1999     

Stability of the polymerizable surfactant stabilized latex particles during semibatch emulsion polymerization

The effect of the polymerizable surfactant, sodium dodecyl allyl sulfosuccinate (JS-2), on the stability of polybutyl acrylate latex particles during semibatch emulsion polymerization was investigated in this work. Experimental data show that the ionic strength is the most important parameter in determining the latex stability during the reaction. Both the amount of coagulum produced by intensive coagulation and percentage of the particle volume change (ΔV) caused by limited flocculation increase with increasing electrolyte concentration. The parameter Δ V increases significantly when the concentration of JS-2 in the initial reactor charge ([JS-2]_i) increases. The amount of coagulum increases rapidly when the agitation speed is increased from 400 to 800 rpm. Experiments of coagulation kinetics were carried out to study the stability of latex products toward added salts. The experimental data show that the chemical stability of the latex product increases with increasing pH. Furthermore, the critical coagulation concentration and diffuse potential increase with increasing [JS-2]_i. It is postulated that the increasing electrostatic attraction force between two approaching particles due to the increased [JS-2] _i can increase the apparent magnitude of Hamaker constant.     

Dextran stabilized poly(methyl methacrylate) latex particles and their potential application for affinity purification of lectins

 Stable poly(methyl methacrylate) latex particles (220–360 nm in diameter) using dextran as the protective colloid were prepared and characterized in this study. Such an emulsion polymerization system follows Smith–Ewart Case III kinetics (i.e., the average number of free radicals per particle is greater than 0.5) due to the relatively large latex particle size. The carbohydrate content of these dextran modified emulsion polymers shows a maximum around 5% dextran based on total monomer weight. The latex stability during polymerization is closely related to the carbohydrate content of these latex particles, and it is controlled by the ratio of the thickness of the dextran adsorption layer to that of the electric double layer of the latex particles. The critical flocculation concentration (CFC) of the latex products correlates well with the latex stability during polymerization. The greater the total scrap produced during polymerization (i.e., the stronger the bridging flocculation), the lower is the CFC of the latex products. The affinity precipitation of concanavalin A (a model lectin used in this study) by the dextran modified PMMA latex particles is also illustrated in this study. The specifically adsorbed concanavalin A increases with the carbohydrate content of the dextran modified latex particles. Received: 9 December 1996 Accepted: 8 April 1997     

Colloidal stability of chitosan-modified poly(methyl methacrylate) latex particles

Experiments of coagulation kinetics were used to study the influence of the electrolyte concentration on the colloidal stability of cationic poly(methyl methacrylate) latex particles with various degrees of chitosan modification. For the chitosan-free latex products prepared by various levels of 2,2′ azobis(2-amidinopropane) dihydrochloride (V-50) at constant pH, the critical coagulation concentration (ccc) increases with increasing V-50 concentration, due to the enhanced particle surface charge density. On the other hand, the chitosan-modified latex products at constant pH do not exhibit very different values of ccc. This result is attributed to the counterbalance between two opposite effects related to the grafted chitosan, that is, the increased particle surface charge density and the enhanced shift of the particle's shear plane toward the aqueous phase with the chitosan content. The ccc of the latex products with various degrees of chitosan modification decreases significantly when the pH increases from 3 to 7. This is because the degree of ionization of the surface amino groups (the particle surface charge density) decreases with increasing pH. As a result, the stability of the colloidal system decreases significantly with increasing pH. The apparent Hamaker constant and diffuse potential were obtained from the coagulation kinetics data. These two parameters along with the zeta potential and particle size data for the latex samples taken immediately after the end of the coagulation experiments were also used to study the effect of ionic strength on the colloidal stability of the latex particles. Received: 10 October 1998 Accepted in revised form: 16 December 1998     

A comparison of the swelling behaviour of copolymer and interpenetrating network microgel particles

 A comparison of the swelling behaviour of two types of hydrogel particles, namely, random poly[(acrylic acid)-co-(acrylamide)] [P(AAc-co-AAm)] particles and PAAc/PAAm interpenetrating network (IPN) particles, has been made using temperature and pH as the triggers. Both types of particles were synthesised by inverse microemulsion polymerisation. The conversion yield of AAc was found to be around 60 wt% due to the partition of this monomer between the aqueous and organic phases. The AAc content was thus lower in the final particles than in the initial composition. Both types of hydrogel particle exhibit an upper critical solution temperature associated with the breakage of the polymer–polymer hydrogen bonds. The maximum swelling ratio occurred in both cases at approximately equimolar AAc and AAm content of the particles. A sharper swelling transition was observed for the PAAc/PAAm IPN particles. This is because of the co-operative nature of the interactions between the PAAc and PAAm chains, the so-called “zipper effect”. A very much higher swelling ratio was obtained using pH as the trigger compared to using temperature. This difference in behaviour is related to the relative strengths of the forces involved in the particle swelling. Electrostatic repulsion forces, associated with the AAc dissociation with increasing pH, are much stronger than the hydrogen bonds. Received: 18 August 1999/Accepted: 28 August 1999     

Polystyrene particles with proton-ionisable groups: pH-dependent stability of latices with weakly acidic groups

 Results of colloid chemical characterisation and stability measurements on electrostatically stabilised latex dispersions made from emulsions of styrene and 4,4′-azobis-(4-cyanovaleric acid) are reported. The deviant stability of the hydrophobic polystyrene particles at low pH and low ionic strength is related to a proton “tunable” hydration layer surrounding weakly charged particles. The idea implies the formation of a polymer-supported surface phase that does not have any clear boundary, either towards the polymer moiety or in the direction of the bulk solution. The formation of the surface phase is controlled by Coulombic, hydrophobic and van der Waals interactions and by the contribution from the water structure at the hydrophobic and hydrophilic domain of the polymer particles. Negative charges on the hydrophobic surface badly interfere with the water structure at the hydrophobic moiety of the particle, whereas positive or uncharged surface groups do not damage the balance of free and clustered water molecules at the interface. Because the hydrophobic nature of the surface changes with the degree of dissociation of the surface charges, the degree of hydrophobicity of the carboxylic latices can be adjusted by changing the pH; therefore, it may be concluded that the hydrated and discharged carboxylic particle is apparently more hydrophobic relative to the ionised one. Thus, our concept can also explain differences in the hydrophobicity of colloidal polymer particles. Received: 12 June 1999/Accepted in revised form: 24 September 1999     

Synthesis and characterization of magnetic and non-magnetic core-shell polyepoxide micrometer-sized particles of narrow size distribution

Core polystyrene microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Uniform polyglycidyl methacrylate/polystyrene core-shell micrometer-sized particles were prepared by emulsion polymerization at 73 degrees C of glycidyl methacrylate in the presence of the core polystyrene microspheres. Core-shell particles with different properties (size, surface morphology and composition) have been prepared by changing various parameters belonging to the above seeded emulsion polymerization process, e.g., volumes of the monomer glycidyl methacrylate and the crosslinker monomer ethylene glycol dimethacrylate. Magnetic Fe(3)O(4)/polyglycidyl methacrylate/polystyrene micrometer-sized particles were prepared by coating the former core-shell particles with magnetite nanoparticles via a nucleation and growth mechanism. Characterization of the various particles has been accomplished by routine methods such as light microscopy, SEM, FTIR, BET and magnetic measurements.     

Cationic amino-containing N-isopropyl- acrylamide–styrene copolymer latex particles: 1-Particle size and morphology vs. polymerization process

 Cationic hydrophilic copolymer latexes were synthesized at 70 °C either by batch or two-step emulsifier-free emulsion poly-merization of styrene (St), N-iso-propylacrylamide (NIPAM), and aminoethylmethacrylate hydro-chloride (AEM) using 2,2′-azobis (2-amidinopropane) dihydrochloride as initiator. At first, batch polymerization kinetics were followed by gas chromatography (GC), revealing that NIPAM rapidly homopolymerized, before the polymerization of styrene had started. Particle size analysis by quasi-elastic light scattering (QELS) and transmission electron microscopy (TEM) showed that monodispersed particles were obtained with the formation of a poly[NIPAM] rich shell. Adding a small amount of the cationic monomer caused a strong decrease of the particle size without affecting the size monodispersity. When a shot process was used, a narrow particle size distribution was maintained, provided that the monomer addition was performed at a relatively high conversion of the first batch step. The poly[NIPAM] rich shell layer was larger with the shot process, but increasing the amino-containing monomer in the recipe resulted in a dramatic decrease of the thickness. Combination of transmission, scanning and atomic force microscopy techniques showed that these hydrophilic particles exhibited odd-shaped structures, the unevenness being dependent upon the performed process. Kinetic data and particle morphology information were inferred for discussion of the polymerization mechanism of this system. Received: 21 August 1997 Accepted: 22 October 1997     

High solids content latexes with low viscosity

The effect of particle size distribution (PSD) on the solids content and viscosity of the multi-sized latex was investigated by blending mono-sized latexes and measuring their rheological properties. The results showed that the maximum packing (highest solids content) was observed at a weight fraction 80% of large particles with respect to total solids content for both bi-modal and tri-modal latexes, and the lowest viscosity was obtained when the ratio of large to medium to small particles was approximately 80/10/10 (by weight). A two-stage technique to prepare high solids multi-sized polymer latex was developed by using a polymer latex previously made as seed and by adding small amount of additional surfactants and/or second group of polymer particles. The PSD of the latex was optimized by varying the amount of the seed, the additional surfactants, and the second group of particles. Film forming latexes with high solids (>65%) and low viscosity were obtained. Received: 18 February 2000 Accepted: 30 September 2000     

Preparation of monodispersed plate-like particles of tungstic acid

 To understand the properties of colloidal dispersions it is often vital to prepare model materials with particles that have a small polydispersity in order to make experimental tests of theories or models. However few preparations have been developed that yield anisotropic particles with a narrow size distribution and precise shape. In this paper the preparation of a dispersion of charge stabilized, tungstic acid particles is described. The particles are rectangular and have a length of 7.0 μm, a width of 2.8 μm and a thickness of 0.2 μm. The polydispersity is 8% in length and 10% in width, making it one of the most monodisperse dispersions of anisotropic particles. Each particle is monocrystalline and the crystal orientation is fixed with respect to the particle morphology. Some interesting behavior is observed: these particles aggregate perpendicular and parallel to each other to give flat, ordered flocs when the stability is reduced. Received: 22 January 1998 Accepted: 4 February 1998     

Preparation and characterization of submicron hybrid magnetic latex particles

Micrometer magnetic hybrid particles are of great interest in biomedical field, and various morphologies have been prepared via encapsulation processes. Regarding submicron, only few processes have been investigated and the most recent one leading to highly magnetic submicron magnetic hybrid particles is based on oil in water magnetic emulsion (MES) transformation. The encapsulation of magnetic iron oxide nanoparticles forming oil in water MES was investigated using different styrene/cross‐linker divinylbenzene volume ratio in the presence of potassium persulfate initiator. The encapsulation performed in this work is basically conducted by using well‐defined oil in water MES as a seed in radical emulsion polymerization. The chemical composition, morphology, iron oxide content, magnetic properties, electrokinetic properties, particle size, and size distribution of the prepared magnetic hybrid particles were examined using various techniques. The desired perfect magnetic core and polymer shell morphology were successfully obtained, and the final magnetic hybrid particles are superparamagnetic in nature and exhibit high iron oxide content (64 wt %). Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and properties of uniform praseodymium-doped ceria colloidal particles

 A procedure to prepare submicrometre spherical particles of Pr(III), Ce(III) or Pr(III)-doped C(III) hydroxycarbonates with narrow size distribution is reported. The particles were obtained by aging aqueous solutions of Pr(III) chloride and/or Ce(III) nitrate in the presence of urea at 100 °C for 2 h. The effect of Pr and/or Ce salt concentrations in the starting solutions on the size, shape and composition of the precipitated particles is reported. The thermal behaviour of the basic carbonates up to decomposition into the metal oxides was followed by differential thermal and thermogravimetric analyses, X-ray diffraction, IR spectroscopy and transmission electron microscopy. All the systems were also characterized by their electrokinetic behaviour (determination of isoelectric point) and specific surface areas. The colour of the powders was also evaluated as a function of the Pr content and temperature and was compared with previous results on red pigments of similar composition. Received: 30 May 2001 Revised: 17 September 2001 Accepted: 20 September 2001     

Preparation and characterization of polydimethylsiloxanes with narrow molecular weight distribution

The preparation of polydimethylsiloxanes (PDMS) of narrow molecular weight distribution (MWD) by anionic polymerization of hexamethylcyclotrisiloxane (D₃) in an improved polymerization apparatus is described. Using (CH₃)₂Si(OLi)₂ as initiator and (CH₃)₃SiCl (TMCS) as terminating agent, polymers with only methyl groups were obtained with molecular weights ranging from 2 × 10³ to 2 × 10⁶. Kinetic investigations were performed only so far as necessary for controlling the polymerization under the chosen experimental conditions (solvent: n-hexane, solvating agent: hexamethylphosphortriamide (HMPT), polymerization temperature: 25°). The molecular weights of the polymers were determined by light-scattering and, after calibration, by viscometry and GPC. The non-uniformities of the samples with symmetrical MWD were estimated using the 4σ-method. The GPC apparatus had been calibrated with polystyrene and poly-α-methylstyrene samples of extremely small non-uniformity.     

Preparation of styrene/acrylonitrile copolymer microspheres and their composites with metal particles

 Monodispersed poly(styrene-co-acrylonitrile) [P(St-co-AN)] microspheres were prepared by emulsifier-free emulsion copolymerization of St with AN. Fourier transform IR spectroscopy and elemental analysis were used to measure the content of AN in the poly(St-co-AN) microspheres. X-ray photoelectron spectroscopy (XPS) measurements indicated the presence of an AN unit on the surface of the microspheres. The combined results of the elemental analysis and the XPS measurements showed that the copolymer on the surface of the P(St-co-AN) particles was rich in AN compared with that in the interior of the particles. P(St-co-AN)–metal composite particles were prepared by chemical metal deposition. The addition of nickel could improve the distribution of cobalt on surface of the polymer microspheres. The preparation of polymer–bimetal composite particles was tried. Transmission electron microscopy and XRD were used to study the distribution and structure of the deposited metal particles. Received: 30 June 1999/Accepted in revised form: 16 September 1999     

Synthesis, characterization and potential biomedical applications of N-succinimidyl ester functionalized, polypyrrole-coated polystyrene latex particles

N-Succinimidyl ester functionalized polypyrrole-coated polystyrene latex particles (PS_E-PPyNSE) were prepared by the in situ copolymerization of pyrrole and the active ester-functionalized pyrrole (pyrrole-NSE) in the presence of polystyrene latex particles. Polystyrene microspheres were prepared by emulsion polymerization (PS_E) leading to particles having a diameter of 450 nm. These PS_E particles were precoated with poly(N-vinylpyrrolidone) prior to the in situ copolymerization of pyrrole and pyrrole-NSE. The initial comonomer concentration fractions were 25/75, 50/50 and 75/25 for pyrrole and pyrrole-NSE, respectively. The PPy-coated PS_E particles were characterized in terms of morphology, particle size, electrophoretic mobility and chemical composition. The study of morphology by means of scanning electron microscopy showed roughening of the underlying PS_E particles owing to the addition of PPyNSE, the overlayer thickness of which was estimated to be around 7 nm. Moreover, loading PPyNSE overlayers resulted in a shift of the electrophoretic mobility from –5.31 m cm/V s to a very small but positive value (0.082–0.112 m cm/V s). X-ray photoelectron spectroscopy and IR spectroscopy permitted the detection of pyrrole-NSE repeat units at the surface indicating that pyrrole and pyrrole-NSE did indeed copolymerize. The PS_E-PPyNSE particles were further evaluated as bioadsorbents of human serum albumin used as a test protein. For this study, PS_E-PPyNSE₅₀ particles, synthesized from a comonomer feed ratio of 50/50 in pyrrole/pyrrole-NSE, were used and were shown to attach efficiently human serum albumin macromolecules with a maximum amount of 0.2 mg m^–2.