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  • Articles: DFG German National Licenses  (35)
  • Polymer and Materials Science  (34)
  • Chemical Engineering  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Emulsion copolymerization of azeotropic styrene-acrylonitrile monomer mixture in polystyrene seed latexes (1985)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 10 (1985), S. 391-402 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 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.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1985.020101985127
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  • 2
    Electronic Resource
    Electronic Resource
    Swelling of carboxyl-containing copolymer latexes (1985)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 10 (1985), S. 335-357 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Methacrylic acid copolymers (5-50%) with methyl methacrylate, styrene, and 2-ethylhexyl acrylate were prepared at 60°C by batch and semicontinuous emulsion polymerization, and the latexes were neutralized with sodium hydroxide. In some cases, ethyl acrylate or crosslinking monomers such as ethylene glycol dimethacrylate, divinylbenzene, or trimethylolpropane triacrylate were added to the recipe. The parameters varied included the Tg of the copolymer, the hydrophobicity of the base monomer, the carboxyl group distribution within the particle, and the degree of crosslinking. The variation of particle size with pH was determined using dissymmetry of light scattering, the variation of viscosity with pH using the Weissenberg Rheogoniometer in the cone-plate mode, and the loci of the carboxyl groups by a modified conductometric titration method. The serum was separated from the latex particles by serum replacement, an excess of sodium hydroxide was added to the cleaned latex, and the conductance and unreacted sodium hydroxide were measured as a function of time. The carboxyl groups were arbitrarily divided into: (i) the particle surface neutralized instantaneously; (ii) the first subsurface layer neutralized within 10 minutes; (iii) the second subsurface layer neutralized within 24 hours; (iv) the unneutralized particle core; (v) the latex serum. The three characterization techniques gave a detailed analysis of the swelling behavior of the carboxyl-containing copolymers. The swelling upon neutralization of the relatively hydrophilic methyl methacrylate copolymers was higher than that of the relatively hydrophobic styrene and 2-ethylhexyl acrylate copolymers. Batch polymerization of the methyl methacrylate copolymers gave a higher concentration of carboxyl groups at or near the particle surface; semicontinuous polymerization gave a more uniform distribution throughout the particle. Decreasing the Tg of the copolymer increased the concentration of carboxyl groups at or near the particle surface. Crosslinking of the particle had little effect on the carboxyl group distribution.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1985.020101985125
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of monomer preemulsification on formation of particles from monomer drops in emulsion polymerization (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 24 (1979), S. 703-707 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Evidence was obtained supporting the theory that monomer droplets can become a locus of initiation and propagation in emulsion polymerization. This was done by reducing the size of the monomer droplets prior to initiation of polymerization using different preemulsification techniques for a typical latex recipe containing a common anionic surfactant. Monomer droplet size reduction caused an increase in the total surface area of the monomer droplets and thereby increased the competitiveness of these droplets for capturing active free radicals which are generated in the aqueous phase. As the total surface area of the monomer droplets was increased by preemulsification, a corresponding increase in the number of large particles formed by polymerization of these monomer droplets was experimentally measured. This work shows that monomer droplets are a locus of emulsion polymerization. However, the importance of monomer droplet polymerization is limited by their total surface area because of the competition for free radicals with other surfaces and/or particle nucleation processes. The results offer a basis for explaining why broad, and sometimes bimodal, particle size distributions are obtained in some commercial processes where the reactants are preemulsified prior to being charged into a reaction vessel.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1979.070240308
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  • 4
    Electronic Resource
    Electronic Resource
    Sulfonated latex particle as acid catalysts for the continuous inversion of sucrose (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 35 (1988), S. 2117-2131 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Sulfonated polystyrene latex particles were used as acid catalysts in the continuous inversion of sucrose at 50-70°C. The particles (surface charge 168 μeq/g) were confined in a stirred reactor with a semipermeable membrane; sucrose solution was pumped in, and product solution was pumped out. The catalytic activity of the particles was unchanged after 20 days continuous use. Variation of particle size (0.13 and 0.42 μm) and stirring rate showed that internal and external mass transfer was not a controlling factor. The kinetics were pseudo-first-order; the rate constant at 70°C was 2.30/N min as compared with 0.07/N min for macroporous sulfonated ion-exchange resin; the apparent activation energy was 111 kJ/mol as compared with 121 kJ/mol for the homogeneous acid-catalyzed reaction. The faster rate was attributed to the very great surface area, high charge density, and lack of internal diffusional resistance of the latex particles. The proposed mechanism comprised adsorption of sucrose on the particle surface, followed by inversion and desorption of product.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1988.070350812
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  • 5
    Electronic Resource
    Electronic Resource
    Uniform polymer particles by dispersion polymerization in alcohol (1986)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 24 (1986), S. 2995-3007 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1986.080241126
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetics of successive seeding of monodisperse polystyrene latexes. I. Initiation via potassium persulfate (1986)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 24 (1986), S. 3499-3513 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization kinetics of monodisperse polystyrene latexes prepared via successive seeding were studied in the region between Smith-Ewart Case 2 (n̄ = 1/2) and Case 3 (n̄ ≫ 1). Potassium persulfate was used as the initiator. The kinetics were measured in a piston/cylinder dilatometer designed for microgravity experiments. A recipe formulation method was developed by which a constant emulsifier (Aerosol-MA) surface coverage was maintained throughout a sequence, beginning with a 0.19 μm polystyrene seed. Monodisperse latexes up to 1 μm in size were prepared using 0.5 mM K2S2O8 with a 4% emulsifier surface coverage. The polymerizations were commenced in Interval III, the particles being swollen with twice their weight in monomer. The kinetics were characterized by the autoacceleration of the gel effect with the overall polymerization rate decreasing with increasing particle size (decreasing Np). The Case 2 to Case 3 kinetic transition was experienced in the first seeding step, however, independence of the rate on the number of particles was not evident even at high values of n̄ (n̄ 〉 10). This was attributed to a dependency of the free radical capture efficiency on the particle size (constant solids). Corroborating indirect evidence was supplied through surface charge analysis and detailed examination of the polymerization kinetics.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1986.080241230
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  • 7
    Electronic Resource
    Electronic Resource
    Phase separation in polystyrene latex interpenetrating polymer networks (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 629-651 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polystyrene/polystyrene latex interpenetrating polymer networks (IPNs) were prepared by seeded emulsion polymerzation of styrene-divinylbenzene mixtures in crosslinked monodisperse polystyrene seed latexes. The resulting latexes comprised uniform nonspherical particles, which were formed by separation of the second-stage monomer from the crosslinked seed network during swelling and polymerization. The kinetics of phase separation were investigated by examining the changes in particle morphology using optical microscopy, which revealed that the phase separation was induced by the relaxation of the polymer chains before polymerization began and was enhanced by increased conversion. The thermodynamics of phase separation were investigated by analysis of the free-energy changes during swelling and polymerization, and the phase separation was described by a nucleation-and-growth mechanism. The results of this study have been applied to the design and synthesis of a series of uniform nonspherical particles of different morphology.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280314
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  • 8
    Electronic Resource
    Electronic Resource
    Preparation of highly sulfonated polystyrene model colloids (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 3187-3199 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous attempts to prepare monodisperse styrene/sodium styrene sulfonate copolymer latexes by batch, seeded, and semicontinuous emulsion polymerization were unsuccessful at high concentrations of the functional comonomer. Broad, and sometimes bimodal, size distributions, and large amounts of water soluble homopolymer were obtained. After removal of free monomer, solute and adsorbed homopolymer and copolymer, the overall incorporation of the functional comonomer was found to be low. To overcome these problems, a two stage “shot-growth” or in situ seeding technique was developed. A first stage copolymerization was carried out with a low concentration of sodium styrene sulfonate: the purpose of the functional comonomer was to enhance the stability and regulate the size of the seed particles. When this reaction had reached high conversion (〉 90%), a second stage monomer mixture was added. The ratio of styrene to sodium styrene sulfonate in this mixture determined the final surface charge density. The mechanism by which the NaSS is incorporated in the polymer particles is considered to be by solution copolymerization with solute styrene monomer to form surface active oligoradicals. These radicals adsorb on the particle surface, initiate polymerization and become inextricably bound, preventing their transfer back to the aqueous phase. By this means, it was possible to vary independently the particle size and surface charge density. High concentrations of functional comonomer could be polymerized without undue wastage (incorporations were only slightly less than 100%) or loss of monodispersity. In extreme cases, the area per functional group fell below the theoretical minimum, indicating considerable hydration of the surface layers.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1989.080271001
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetics of successive seeding of monodisperse polystyrene latexes. II. Azo initiators with and without inhibitors (1986)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 24 (1986), S. 3515-3527 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oil soluble azo initiators in combination with water soluble inhibitors were used to extend the particle size limit in studies of the kinetics of successive seeding of monodisperse polystyrene latexes. Monodisperse latexes were prepared up to 2.5 μm in diam using 4.0 mM AMBN and 14.5 mM hydroquinone with a constant 15% emulsifier (Aerosol-MA) surface coverage throughout the seven step sequence. The polymerization kinetics were measured in a piston/cylinder dilatometer designed for microgravity experiments. The Interval III kinetics were dominated by the gel effect although these were affected by the nature of the inhibitor. In general, the overall polymerization rate decreased with increasing particle size (decreasing Np) up to a size of about 1 μm. Thereafter, the kinetics were independent of these variables, exhibiting Smith-Ewart Case 3 (bulk) kinetics. The initiator efficiencies were found to be of the order of 10%, considerably lower than reported for bulk polymerizations.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1986.080241231
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  • 10
    Electronic Resource
    Electronic Resource
    Morphology and grafting reactions in core/shell latexes (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1219-1233 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The particle morphology and percent grafting were investigated as a function of the crosslink density of the seed latex in two systems of core/shell latexes of polybutadiene/polymethyl methacrylate (PB/PMMA) and styrene-butadiene rubber/polymethyl methacrylate (SBR/PMMA) prepared by seeded emulsion polymerization at 50°C. The thin layer chromatography/flame ionization detection (TLC/FID) technique was used to characterize the grafting efficiency of the core/shell latexes. The percent grafting of the shell polymer was found to decrease with increasing the crosslink density of the core material. The particle morphology and precent grafting were also investigated as a function of composition and structure of the core material in four core/shell latex systems: polybutadiene/styrene-acrylonitrile copolymer (PB/SAN), (styrene-butadiene) random copolymer/styrene acrylonitrile copolymer (S:B/SAN), polystyrene : polybutadiene/styrene-acrylonitrile copolymer (PS:PB/SAN) and Kraton/styrene-acrylonitrile copolymer (Kraton/SAN), which were prepared by direct emulsification for the seed followed by emulsion polymerization at 70°C for the shell polymer. Grafting and crosslinking of the core material were found to be competitive reactions depending on the microstructure of the seed latex.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080250503
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