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ABSTRACT: Emulsion copolymerizations involving water-soluble functional monomers such as N-methylolacrylamide often result in the formation of water-soluble polymer that remains in the aqueous phase of the latex. A simple procedure is developed to determine the amount of water-soluble polymer in the aqueous phase of a high-solids latex using ultracentrifugation. Dilution of the latex with water is usually found necessary for good separation during ultracentrifugation. If the latex contains a surface-active species ( surfactant) in amounts comparable to the amount of water-soluble polymer, calculation of the amount of water-soluble polymer in the serum of the original latex will require information about dilution dependent partitioning of the surfactant between the surface of the particles and the aqueous phase. This paper outlines a procedure that enables determination of the amount of water-soluble polymer in the aqueous phase of the original latex, by ultracentrifugation of the latex diluted to different concentrations. The procedure also gives the Henry's constant for the adsorption of the surfactant on the surface of the polymer particles in the latex.
Colloid and Polymer Science. 01/2005; 283(8):836-844.
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ABSTRACT: Oxygen-free conditions are required during emulsion polymerization reactions to eliminate the inhibition effect of oxygen on the free-radical mechanism of polymerization. Results of a kinetic study of the emulsion polymerization of n-butyl methacrylate using a 1-dm(3) reaction calorimeter indicate that oxygen, even in concentrations as low as 1 ppm, not only prolongs the induction period that precedes the chain propagation but also influences the particle nucleation and molecular weights. Agitation promotes the transfer of residual oxygen from the reactor headspace into the emulsion and, therefore, has an effect on the particle nucleation step and other reaction events that follow.
Industrial & Engineering Chemistry Research. 01/2004; 43(20):6331-6342.
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10/2003;
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ABSTRACT: The grafting of methyl methacrylate (MMA) onto polybutadiene (PB) latexes prepared by seeded emulsion polymerization at 50°C was investigated as a function of: (a) initiator concentration used in the secondary polymerization, (b) monomer-to-polymer ratio, (c) the specific surface area of the seed latex, and (d) the degree of conversion. The thin layer chromatography/flame ionization detection (TLC/FID) technique was used to determine the proportion of graft copolymer in the core/shell latex, It was found that grafting PMMA onto PB depended upon the concentration of initiator, decreasing as the concentration was increased. The amount of grafting increased with increasing specific surface area of the seed latex, while the molecular weight of the acetone-soluble graft copolymer decreased. The amount of graft copolymer was found to decrease concurrently with increasing monomer-to-polymer ratio and degree of conversion. These results suggest a hydrogen abstraction mechanism in the formation of graft PB–PMMA through a chain transfer process.
Journal of Polymer Science Part A Polymer Chemistry 04/2003; 25(7):1755 - 1767. · 3.92 Impact Factor
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ABSTRACT: The effects of comonomer composition and the method of monomer addition on the compositional homogeneity and the colloidal properties of (vinyl acetate-butyl acrylate) copolymer latexes were investigated. Particle size and distribution, and the surface characteristics of the copolymer latexes were found to vary with the comonomer composition and the type of the polymerization process. The aging of the latexes affects the surface properties and by that the colloidal stability against electrolytes. Branching, hydrolysis, flexibility of the molecules and heterogeneity of the latex particles appear to play a major role for the stability of the latexes.Der Einfluß der Comonomerzusammensetzung und der Art der Monomerzugabe auf die Homogenität und die kolloidalen Eigenschaften von Vinylacetat-Butylacrylat-Copolymerlatices wurde untersucht. Die Teilchengröße und ihre Verteilun sowie die Oberflächeneigenschaften der Copolymerlatices hängen von der Comonomerzusammensetzung und der Prozeßführung ab. Eine Alterung der Latices beeinflußt die Oberflächeneigenschaften und damit die Kolloidstabilität gegenüber Elektrolyten. Verzweigung, Hydrolyse und Flexibilität der Moleküle sowie die Heterogenität der Latexpartikeln scheinen für die Stabilität der Latices eine große Rolle zu spielen.
Acta Polymerica 04/2003; 32(10):583 - 592.
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ABSTRACT: The azeotropic 80:20 styrene-acrylonitrile mixture was polymerized in 190nm- and 300nm-diameter monodisperse polystyrene seed latexes by batch, batch-with-equilibrium-swelling, and semi-continuous polymerization. Polystyrene seed latexes were used to determine the degree of grafting of the substrate as well as the styrene-acrylonitrile copolymer. The Arrhenius plot of log (polymerization rate) of the seeded batch copolymerizations with reciprocal temperature comprised two linear regions with a sharp inflection point at 65°C. Specific volume measurements showed that the Tg of the monomer-swollen styrene-acrylonitrile copolymer was also 65°C. The final latex comprised the original seed particles grown to a larger size and, in some cases, a new crop of particles formed during the polymerization. The critical factor determining the formation of new particles was the surface area of the seed latex: at or above 226 m2/dl, new particles were not formed; at or below 179 m2/dl, a new crop of particles was nucleated, the number increasing with decreasing surface area. The degree of grafting of the polystyrene seed substrate was greater for the smaller particle size seed latex, and increased exponentially with increasing seed surface area. The amount of grafted styrene-acrylonitrile copolymer determined the stability of the grafted particles in acetone, a good solvent for the copolymer. Dynamic mechanical spectroscopy showed that the continuous phase was either the polystyrene substrate (Tg 104°C) or the styrene-acrylonitrile copolymer phase (Tg 120°C) except where the degree of grafting was high, in which case, the Tg was intermediate between the two values. Electron microscopy of thin film sections stained with ruthenium tetroxide confirmed which phase was continuous and showed interpenetrating networks for those systems of intermediate Tg.
Die Makromolekulare Chemie 03/2003; 10(S19851):391 - 402.
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ABSTRACT: Polymerization of styrene miniemulsions, prepared using a mixed emulsifier system comprising sodium lauryl sulfate and cetyl alcohol, was carried out using both water-soluble (potassium persulfate) and oil-soluble [2,2′-azobis-(2-methyl butyronitrile)] initiators. The effects of variation of initiator concentration, polymerization temperature, and added inhibitor on the kinetics and particle-size distributions were investigated to obtain more quantitative evidence concerning the locus of polymerization in miniemulsion systems. Experimental results for the kinetics and particle-size distributions clearly showed that monomer droplets became the main source of polymer particle formation. This was attributed to the fact that stable emulsions with droplet diameters in the range of 0.05 to 0.15 μm were produced using this mixed-emulsifier system. In this size range, droplet initiation could effectively compete with other mechanisms due to their large surface area. Their size was indeed similar to the corresponding latex particle size obtained after polymerization.
Journal of Polymer Science Polymer Chemistry Edition 03/2003; 23(12):2973 - 2987.
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Journal of Polymer Science Part C Polymer Letters 03/2003; 11(8):503 - 513.
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ABSTRACT: Vinyl acetate (VAc)–butyl acrylate (BuA) comonomer mixtures with various composition were polymerized by batch and semicontinuous emulsion polymerization processes. PVAc and PBuA homopolymer latexes as well as the (VAc-BuA) copolymer latexes were characterized with respect to particle size, molecular weight, acid end groups on particle surfaces, and colloidal stability against electrolytes. The surface and colloidal properties of these latexes were also compared before and after aging and acid hydrolysis. The average particle size of batch latexes was independent of copolymer composition, whereas for semicontinuous latexes it decreased with increasing BuA content and was always lower than that of the corresponding batch latex. The molecular weight distribution (MWD) for batch latexes was narrower and much less dependent on composition than that of the semicontinuous latexes; bimodal MWD was found in most semicontinuous latexes with a substantial amount of low MW fraction. The total weak and strong acid end groups on particle surfaces for semicontinuous latexes is higher, and more dependent on composition, than the batch latexes. Acid-induced hydrolysis results in a drastic change in the type and concentration of the surface groups of the semicontinuous latex particles. Colloidal stability against electrolytes showed that both electrostatic (due to surface acid groups) and steric [due to surface poly(vinyl alcohol)] mechanisms are contributing. However, for semicontinuous latexes, increasing PVAc content above 50 mol % resulted in a proportional increase and ultimately dominant role of steric stabilization. The results were interpreted in terms of differences in reactivity ratios and water solubilities of the two monomers and their effects on the locus of initiation and growth in the two polymerization processes, as well as the monomer sequence within the polymer chain and degree of homogeniety of the copolymer composition within the particle.
Journal of Polymer Science Polymer Chemistry Edition 03/2003; 21(8):2363 - 2382.
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ABSTRACT: Vinyl acetate/(VAc)-butyl acrylate/(BuA) copolymer latex films of various copolymer compositions were investigated for their morphological properties by electron microscopy techniques, and for their mechanical properties by dynamic mechanical spectroscopy (DMS), differential scanning calorimetry (DSC), and tensile strength measurements. Batch copolymer latex films showed domains of PBuA dispersed in PVAc matrix; the domain sizes were increased with increased BuA content. Semicontinuous latex films were homogeneous in composition. Glass transition temperatures Tg determined from DMS and DSC indicated the presence of two, low and high, transition temperatures for batch latex films. The two temperatures approached the individual homopolymers, with increased PBuA content up to 51 mol %. Semicontinuous latex films showed only one single Tg. Tensile properties of the batch copolymer films showed a higher ultimate tensile strength, higher Young's modulus, and lower percent elongation to break compared to semicontinuous latex films. These differences were found to reflect the effect of mode of monomer addition during the emulsion copolymerization process on the particle morphology, and confirmed earlier data on bulk, colloidal, and surface properties of the same copolymer latexes.
Journal of Polymer Science Polymer Chemistry Edition 03/2003; 21(8):2383 - 2396.
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ABSTRACT: A thermodynamic model has been proposed for the simulation of monomer partitioning behavior in the dispersion polymerization of styrene in ethanol. The monomer concentration in the polymer particles is very low (20 vol% at 5% conversion) and decreases further as the polymerization proceeds. It is independent of stabilizer concentration but is strongly dependent on initial monomer concentration. The partitio n coefficient ([Mp]/[Mc]) of styrene increases from 0.8 to 1.1 with incresing conversion. There are two polymerization loci in dispersion polymerization, namely the continuous and polymer phases. Competition between solution and heterogeneous polymerization has been observed in this system. The rate of dispersion polymerization is dependent on initial monomer concentration but is independent of initiator concentration at higher conversions. The molecular weight of the polymers produced by this process increases with increasing conversion and decreases with increasing initiator concentration.
Journal of Polymer Science Part B Polymer Physics 03/2003; 26(6):1187 - 1203. · 1.53 Impact Factor
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ABSTRACT: The stability against electrolytes for all-sulfate, all-carboxyl, and all-hydroxyl, polystyrene model latexes followed the order, sulfate > carboxyl > hydroxyl when determined from an IR light scattering technique. Two types of hydroxyl endgroups were identified by 13C-NMR (chemical shift correlations, and model compound comparisons), for the polystyrene model latexes. One type was due to termination of growing chain with an oligomer with a single monomer unit, and the other due to termination of growing chains. The surface hydroxyl groups of an all-hydroxyl latex were derivatized with hexafluoroacetone, and quantified using 19F-NMR techniques. Good agreement with the indirect conductometric titration values were obtained.
Journal of Polymer Science Polymer Chemistry Edition 03/2003; 23(11):2819 - 2832.
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Journal of Polymer Science Part C Polymer Letters 03/2003; 17(9):567 - 572.
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ABSTRACT: A new approach is presented to calculate both the distribution of particles with iradicals and the average number of radicals per particle in emulsion polymerizations carried out using oil-soluble initiators. The convergence and accuracy of the approach were examined. It was found that, in agreement with previously published experimental results, the present approach predicts a kinetic behavior similar to that found for water-soluble initiators. This effect is primarily due to the desorption of initiator radicals from the polymer particles rather than the contribution of the fraction of oil-soluble initiator dissolved in the aqueous phase.
Journal of Polymer Science Part A Polymer Chemistry 03/2003; 27(11):3569 - 3587. · 3.92 Impact Factor
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ABSTRACT: Experimental conditions for preparing monodisperse, micron-size poly(butadiene/styrene) particles by dispersion polymerization were investigated. After some initial recipe development, the following variables were fixed: butadiene/styrene weight ratio (90/10), dispersion medium (ethanol), polymeric stabilizer [poly(vinyl pyrrohdone), K-30], costabilizer (sodium dioctyl sulfosuccinate), initiator (2,2′-azobisisobutryonitrile), and polymerization temperature (70°C). The primary process variables investigated were the monomer/ethanol ratio (M/S), the rpm of the bottle polymerizer, and the amount of free space (FS) in the polymerization bottles. The particle size varied from 0.77 to 1.8 μm and was found to increase with increasing M/S and rpm, and decreasing FS. © 1995 John Wiley & Sons, Inc.
Journal of Applied Polymer Science 03/2003; 55(10):1411 - 1415. · 1.29 Impact Factor
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ABSTRACT: Monodisperse poly(divinylbenzene) and poly(styrene-co-divinylbenzene) particles were prepared in the 0.4−3 μm size range by dispersion polymerization in methanol and methanol/co-solvent mixtures. The effects of polymerization parameters, such as the crosslinking monomer concentration, the co-solvent, and the presence of oxygen were studied. For good colloidal stability, it was necessary to use a relatively large fraction of crosslinking monomer. The initial presence of oxygen was also found to play an important role in determining the colloidal stability during the polymerization. Although the exact mechanism is not certain, it is considered likely that the oxygen promotes the grafting of poly(divinylbenzene) to the polyvinylpyrrolidone (PVP) stabilizer molecules. The growing particles were investigated by electron microscopy. Precipitation of small particles onto the nucleated particles was determined to be the primary mechanism of particle growth. © 1993 John Wiley & Sons, Inc.
Journal of Applied Polymer Science 03/2003; 50(11):2027 - 2034. · 1.29 Impact Factor
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ABSTRACT: The mechanism for the formation of micron-size polymer particles in the dispersion polymerization of methyl methacrylate was investigated by applying dynamic light scattering to monitor the evolution of the average particle size in the early stages of the polymerization. In addition, the contributions of physically adsorbed stabilizer and graft copolymer were evaluated by measuring the bound, unbound (adsorbed), and free stabilizer, and by determining the amount of added stabilizer required in seeded dispersion polymerizations. Twenty nanometer particles (termed nuclei) were the smallest particles detected and are considered to be formed by aggregation of growing polymer chains precipitating from solution as they exceed their critical chain length. Aggregation of these nuclei with themselves and their aggregates continues until mature and stable particles are formed. This occurs when sufficient stabilizer occupies the particle surface which includes both the polymeric stabilizer [poly(vinylpyrrolidone)] and its graft copolymer which is created in situ. The effects of process variables are discussed based on this mechanistic picture of the dispersion polymerization process. © 1994 John Wiley & Sons, Inc.
Journal of Polymer Science Part A Polymer Chemistry 03/2003; 32(6):1087 - 1100. · 3.92 Impact Factor
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ABSTRACT: A polymerizable surfactant, sodium dodecyl allyl sulfosuccinate (TREM LF-40; Henkel) and its nonpolymerizable counterpart were used in comparative studies of the emulsion polymerization of vinyl acetate. The conversion-time behavior differed for the two surfactants; the TREM LF-40 showed a decrease in the polymerization rate with increasing concentration while its hydrogenated derivative showed the opposite behavior, the rate increasing with increasing surfactant. Particle size analysis revealed a decreasing particle size with increasing surfactant concentration for both series of reactions. An explanation for the seemingly ambiguous results obtained for the polymerizable surfactant was sought by examining the reactivity of its vinyl group in copolymerization with vinyl acetate and its allylic group in a chain transfer reaction. The results suggest that both the copolymerization and chain transfer reactions can lead to the observed reduction in polymerization rate with increasing TREM LF-40 concentration. © 1992 John Wiley & Sons, Inc.
Journal of Polymer Science Part A Polymer Chemistry 03/2003; 30(12):2619 - 2629. · 3.92 Impact Factor
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ABSTRACT: A mathematical model was developed to simulate the polymerization kinetics of styrene oil-in-water microemulsions. Nucleation of particles in microemulsion droplets was assumed to account for the number of particles generated. It was found that the entry rate coefficient of radicals into microemulsion droplets is much smaller than the entry rate coefficient into monomer-swollen particles. All particles contain at most one growing radical. Various radical entry mechanisms were evaluated using the simulation. The possibility of flocculation between particles during the later stages of the polymerization and the high desorption rate of monomeric radicals was suggested by the simulation results. The likelihood of re-entry of desorbed radicals was den onstrated.
Journal of Polymer Science Part A Polymer Chemistry 03/2003; 30(5):703 - 712. · 3.92 Impact Factor
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ABSTRACT: Uniform polystyrene particles in 1–10 μm size range and up to 40% solid contents have been prepared by polymerizing styrene in ethyl alcohol with azo-type initiators and a polymeric stabilizer polyvinylpyrrolidone along with an anionic, nonionic, or comonomeric co-stabilizer. Effects of polymerization parameters, such as monomer concentration, type of co-stabilizer, initiator type and concentration, crosslinking monomer, and diluent on average particle size and size distribution have been studied. Functional groups such as hydroxyl, carboxyl, amine, amide, silane, polydimethylsiloxane, and silacrown have been successfully incorporated onto the particles by copolymerization. A mechanism for particle formation and growth in dispersion polymerization is presented.
Journal of Polymer Science Part A Polymer Chemistry 03/2003; 24(11):2995 - 3007. · 3.92 Impact Factor
