Studies on the preparation and characterization of monodisperse polystyrene latices. VI. Preparation of zwitterionic latices

The preparation of zwitterionic latex particles is reported by using a mixed anionic and cationic initiator system without requiring surface-active agents. Isoelectric points were found from microelectrophoresis experiments and were in the pH range of 3.5-5. Close to the isoelectric point, the latices coagulated as expected, and good stability was achieved outside this narrow range. This range of stability was in good agreement with predictions from current theory. Redispersion after coagulation was found to be difficult as was expected for a hydrophobic colloid. The electrokinetic behavior did not result in the maximum in zeta potential at an electrolyte concentration of 1 mM unlike the situation for other hydrophobic polystyrene latex particles, and hence these systems may be even better models for other colloidal studies.     

Preparation of monodisperse polystyrene latices

Summary A series of monodisperse polystyrene latices was prepared by using the direct and the seeding emulsion polymerization methods. The recipes for their preparation are given in full detail. Best results were obtained when using Aerosol MA (a surfactant of the sulfosuccinate series) as the emulsifier. The particle size distributions were evaluated from electron microscopic data. The average size of latex particles ranged from 200 to 950 m. The polydispersity ratios being very near unity and modal frequencies about 95% indicate a very high monodispersity of latex preparations. The reproducibility of the particle size distribution parameters was remarkably good. Significant deviation from theSmith-Ewart mechanism was found. A possible mechanism of the emulsifier action in the formation of monodisperse latices is postulated.

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Zusammenfassung Es wurde eine Serie von monodispersen Polystyrollatices dargestellt. Die experimentellen Bedingungen, unter welchen monodisperse Latices entstehen, wurden untersucht. Die Vorschriften sind genau angegeben. Mit Aerosol MA (einem oberflächenaktiven Mittel der Sulfosuccinatserie) als Emulgator wurden die besten Ergebnisse erhalten. Mittels Elektronenmikroskopie wurde die Verteilung der Teilchengrößen ermittelt. Die durchschnittliche Größe der Latexteilchen lag zwischen 200 und 950 m. Die Polydispersitätsquotienten lagen in unmittelbarer Nähe von 1, und die modalen Frequenzen um 95% indizierten eine sehr hohe Monodispersität der Latexproben. Die Reproduzibilität der Teilchengröße-Verteilung-Parameter war besonders ausgeprägt. Es wurde eine Abweichung vomSmith-Ewart-Mechanismus beobachtet. Der mögliche Mechanismus der Emulgatorwirkung bei Entstehung der monodispersen Latices wurde diskutiert.

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With 7 figures and 8 tables     

Preparation and characterization of detergent-free monodisperse polystyrene latices of small particle size

Summary The preparation has been described of detergent-free monodisperse polystyrene latices with particle diameters in the order of 200 nm. Conductometric titration shows the surface charge of the dispersed particles to consist mainly of carboxyl groups. Sulphate groups, if present, can be eliminated by oxidation with persulphate. The surface charge can be varied over a rather large range.Coagulation concentrations for K⁺ are found to be pH-dependent, unlike those for Mg²⁺. Coagulation with Ba²⁺ follows a somewhat capricious pattern, possibly due to specific interaction of these ions with the stabilizing surface entities.From the coagulation concentrations for K⁺ and Mg²⁺ and the corresponding-potentials, Hamaker constants for mutual attraction,A, have been calculated according to the DLVO-theory. TheseA-values show but little variation. Their average value,A = 9.9 × 10^–21 J, compares favourably with the outcome of calculations based on the Lifshits theory and with experimental values obtained for latices with larger particles that have been prepared in different ways.

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Zusammenfassung Es wird beschrieben, wie man tensidfreie Polystyroldispersionen mit Teilchendurchmessern in der Größenordnung von 200 nm herstellen kann. Konduktometrische Titrationen zeigen, daß die Oberflächenladung hauptsächlich von Carboxylgruppen gebildet wird. Oberflächensulphatgruppen können durch Oxidierung mit Persulphat beseitigt werden. Die Größe der Oberflächenladung kann ziemlich breit variiert werden.Die Flockungskonzentration für K⁺ ist pH-abhängig; die für Mg²⁺ aber nicht. Die Flockung mit Ba²⁺ benimmt sich ein wenig kapriziös, vielleicht weil spezifische Interaktion mit Oberflächengruppen stattfindet.Die Flockungskonzentrationen für K⁺ und Mg²⁺ ermöglichen, zusammen mit den entsprechenden-Potentialen, die Berechnung der Hamakerkonstanten für gegenseitige Attraktion,A, aus der DLVO-Theorie. DieseA-Werte sind sich ziemlich gleich. Ihr Mittelwert,A = 9.9 × 10^–21 J, verhält sich günstig zu denen, welche auf Grund der Lifshits-Theorie berechnet wurden, und zu experimentellen Werten für Latices mit größeren Teilchendurchmessern, die in anderer Weise hergestellt wurden.

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With 2 figures and 2 tables     

Nonionic latices in aqueous media part 1. Preparation and characterization of polystyrene latices

A series of non-ionic polystyrene latices in aqueous media containing particles with a narrow size distribution have been prepared using a nonyl phenol poly(ehylene glycol) condensate as the surfactant, methoxy poly(ethylene glycol methacrylate) as the comonomer/stabilizer, and ascorbic acid/hydrogen peroxide as the initiator system. As a control synthesis for comparison with the above latex, a charge stabilized polystyrene latex was prepared, using an anionic surfactant and potassium persulphate as the initiator. Latices employing a combination of charge plus steric stabilization mechanisms were also prepared, in order to investigate the effect of the non-ionic surfactant and the comonomer/stabilizer. The particle size of the latices was measured by transmission electron microscopy, the surface charge density by conductimetric titration and the glass transition temperature of the polymer by differential scanning calorimetry. The latex prepared using non-ionic ingredients, showed no titratable charge and exhibited a profound lowering of the glass transition temperature, with respect to the charge stabilized latex. On the basis of these results, schematic models for the polymerization mechanism and the morphology of the latex particles are proposed.     

Problems associated with the surface characterization of polystyrene latices

It has been shown that polystyrene latices prepared by the surfactant free emulsion polymerization process often contain sufficient residual monomer and possibly low-molecular-weight material and reaction by-products, such as benzaldehyde, which are not efficiently removed by dialysis, to affect their bulk and surface characteristics. These materials have been identified by gel permeation chromatography (GPC) and infrared (IR) spectroscopy studies and their effective removal by steam stripping has been investigated. Steam stripping has proved to be efficient in this process but it led to rapid hydrolysis of the surface sulfate groups and a consequent change in the surface characteristics. The problem of hydrolysis of sulfate groups under various environments has been studied. The problems associated with the identification of weak acid end groups are discussed and several alternative explanations for their occurrence are advanced.     

Studies of particle-particle interactions using polystyrene latices and time-average light scattering

Dilute dispersions of monodisperse negatively-charged polystyrene latex particles, radii 161 Å, have been examined by time-average light scattering at various latex volume fractions and electrolyte concentrations. The latter were varied from the low value produced by maintaining mixed bed ion-exchange resin beads in the systems (ca. 10^–5 mol dm^–3) to the value of 5×10^–3 mol dm^–3 obtained by the addition of sodium chloride. From angular scattering measurements determinations of the structure factors were made; these were produced as a consequence of the particle-particle interactions in the system. By extrapolation of the structure factor to zero scattering angle, values were obtained for the osmotic compressibility and hence the osmotic pressure of the systems as a function of the latex volume fraction. It was found that the experimental data obtained could be interpreted in terms of a hard-sphere model for the particle-particle interaction. Good agreement was obtained provided that the particles were assigned a hard-sphere radius which was determined by the electrostatic repulsion between the particles.     

Synthesis and characterization of cationic amino functionalized polystyrene latexes

Amino-functionalized latex particles were obtained batchwise by emulsion copolymerization of styrene and vinylbenzylamine hydrochloride (VBAH) in the presence of 2-2-Azobis(2-amidinopropane) HCl (V50). Size monodispersity of the particles was improved by using divinylbenzene (DVB) as a third monomer at a 2% molar ratio. Surface amino group titration was performed spectrometrically with N-succinimidyl 3-(2 pyridyldithio)propionate (SPDP). The yields of functional monomer incorporation were up to 85%.     

Studies on preparation and stability of styrene-methyl methacrylate and styrene -methacrylic acid copolymer latices

Summary Series of styrene-methyl methacrylate (SM) and styrene-methacrylic acid (SA) copolymer latices have been prepared by emulsion polymerization using polyoxyethylene nonyl phenyl ether as emulsifier and potassium persulphate as initiator. Trace carboxyl groups were detected both in polystyrene latex and styrene-methyl methacrylate copolymer latices. The stability and electrophoretic behaviour of these latices against barium chloride have been investigated. The values of the critical coagulation concentration (c. c. c.) increased with increasing methacrylic acid content for SA series latices, while they are almost independent of methyl methacrylate content for SM series latices. The effects of methyl methacrylate and methacrylic acid on the change in Hamaker constant were found to be almost identical. The difference inc. c. c. between SM and SA series latices seems to be due to the difference in electrical repulsion caused mainly by carboxyl groups on the surface.

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Zusammenfassung Eine Serie der Styrol-Methyl-Methacrylat (SM) und Styrol-Methacrylsäure (SA) Mischpolymer-Latices wurde unter Verwendung von Polyoxyäthylennonylphenyläther als oberflächenaktives Agents und Kaliumpersulfat als Initiator von Emulsionspolymerisation hergestellt. Wenige Carboxylgruppen in beiden Polystyrol-Latex-und Styrol-Methyl-Methacrylat-Mischpolymer-Latices wurden gefunden. Stabilität und elektrophoretische Beweglichkeit dieser Latices gegen Bariumchlorid würden untersucht. Die Werte der kritischen Koagulaiionskonzentration (k. k. k.) nahm mit Zunahme des Gehaltes an Methacrylsäure für SA-Latices zu, während sie fast unabhängig vom Gehalt an Methyl-Methycrylat für SM-Latices sind. Die Wirkungen des Methyl-Methacrylats und der Methacrylsäure auf die Änderung der Hamaker Konstante sind meistens identisch. Der Unterschied in k. k. k. zwischen SM- und SA-Latices scheint hauptsächlich auf den Unterschied in der elektrischen Abstoß durch Carboxylgruppen auf der Oberfläche zuzückgeführt werden zu können.

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With 4 figures, and 2 tables     

Titanium compounds as coatings on polystyrene latices and as hollow spheres

Sub-micron-sized anionic polystyrene latices have been coated with uniform layers of amorphous titanium dioxide by hydrolysis of titanium tetrabutoxide in ethanolic solutions containing the polymer cores. The thickness of the coating layer could be altered by adjusting the concentration of titanium tetrabutoxide and the amount of polymer latex added to the system. Hollow colloidal spheres of crystal titanium dioxide were obtained by calcination of the so-coated polystyrene latices at an elevated temperature. Received: 29 July 1999/Accepted in revised form: 15 October 1999     

Hematite nanoparticles as polystyrene microsphere coatings and hollow spheres: preparation and characterization

A novel method of fabricating composite particles with core–shell structures is demonstrated. The particles comprised monodisperse submicrometer-sized copolymer latex spheres as cores and Fe₂O₃ crystallites as shells. The shell was formed by controlled hydrolysis of aqueous iron solutions, and the growth of hematite on the surface of the copolymer spheres was controlled by slow injection. Hollow spheres were obtained by calcinations of the so-coated copolymer lattices at 500°C in air. The void size of these hollow spheres was determined by the diameter of the copolymer template, and the wall thickness could be easily controlled in the range of 20–60 nm by using this coating process. The structure and the composition of the spheres were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). It can be seen that a crystallite change and a crystal phase transformation occurred during coating and calcination of the composite spheres. The formation of the composite particles is simply explained by the nucleation of iron oxide on the surface of the latex followed by growth of the iron compound shell.     

Synthesis and characterization of cationic tungsten(V) methylidynes

Cationic tungsten(V) methylidynes [L4W(X)[triple bond]CH]+[B(C6F5)4]- [L = PMe3, 0.5dmpe (dmpe = Me2PCH2CH2PMe2), X = Cl, OSO2CF3] have been prepared in high yield by a one-electron oxidation of the neutral tungsten(IV) methylidynes L4W(X)[triple bond]CH with [Ph3C]+[B(C6F5)4]-. The ease and reversibility of the one-electron oxidation of L4W(X)[triple bond]CH were demonstrated by cyclic voltammetry in tetrahydrofuran (E1/2 is approximately -0.68 to -0.91 V vs Fc). The paramagnetic d1 (S = 1/2) complexes were characterized in solution by electron spin resonance (g = 2.023-2.048, quintets due to coupling to 31P) and NMR spectroscopy and Evans magnetic susceptibility measurements (mu = 2.0-2.1 muB). Single-crystal X-ray diffraction showed that the cationic methylidynes are structurally similar to the neutral precursor methylidynes. In addition, the neutral (PMe3)4W(Cl)[triple bond]CH was deprotonated with a strong base at the trimethylphosphine ligand to afford (PMe3)3(Me2PCH2)W[triple bond]CH, a tungsten(IV) methylidyne complex that features a (dimethylphosphino)methyl ligand.     

Preparation and characterization of cationic polystyrene latex particles of different aminated surface charges

Functionalized polystyrene latex particles were obtained either by seed particle functionalization or by the shot-growth procedure using 2,2′-azobis (2-amidino-propane) dihydrochloride as an initiator and vinylbenzylamine hydrochloride as a cationic monomer. The capabilities of both processes to produce functionalized particles in terms of functionalization yields coming from surface amino group titrations were compared. Different titration methods were performed and a new technique was introduced using fluorescamine.     

Simple method for immobilization and characterization of cationic indicators on an optically clear polystyrene surface

A simple method to immobilize cationic indicators onto the surface of disposable polystyrene cuvettes is described. The cuvettes are sulfonated simply by exposure to sulfuric acid; cationic indicators then bind to the sulfonated polystyrene surface by electrostatic attractions. Following immobilization, the cuvettes can be used for analytical work and in classroom demonstrations, or machined into reusable sensor strips, or disks suitable for use with optical fibers.     

A study of some of the rheological properties of concentrated polystyrene latices

Monodisperse latices form highly ordered but liquid-like structured dispersions at moderate to high concentrations. The rheological measurements show such systems to be viscoelastic. Shear wave propagation and creep compliance measurements have been carried out as a function of volume fraction using polystyrene latices in dilute electrolyte. These measurements enabled the high frequency limiting modulus and the zero shear rate viscosity to be obtained.The data are compared with predictions from models based on the perturbation of ordered particle structures, the magnitude of the particle pair potentials and the restricted diffusive motion of particles in the structures.     

Some novel mesoionic bispurinone analogs: Studies on preparation and characterization

The preparation of the first examples of class II mesoionic bispurinones is described. Arylaminobithiazole 3 is cyclized by condensation with bis(2,4,6-trichlorophenyl) methylmalonate to yield anhydro 3,3′-bis(6-methyl-8-aryl-5-hydroxy-7-oxothiazolo[3,2-a]pyrimidinium hydroxide).