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  • Polymer and Materials Science  (7)
  • Physics
  • 1990-1994  (7)
  • 1994  (7)
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  • 1990-1994  (7)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Free radical exit in emulsion polymerization. I. Theoretical model (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 605-630 
    Details
    ISSN: 0887-624X
    Keywords: free radical ; exit ; emulsion ; polymerization ; model ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The exit or desorption of free radicals from latex particles is an important kinetic process in an emulsion polymerization. This article unites a successful theory of radical absorption (i.e., initiator efficiency), based on propagation in the aqueous phase being the rate determining step for entry of charged free radicals, with a detailed model of radical desorption. The result is a kinetic scheme applicable to true “zero-one” systems (i.e., where entry of a radical into a latex particle already containing a radical results in instantaneous termination), which is still, with a number of generally applicable assumptions, relatively simple. Indeed, in many physically reasonable limits, the kinetic representation reduces to a single rate equation. Specific experimental techniques of particular significance and methods of analysis of kinetic data are detailed and discussed. A methodology for both assessing the applicability of the model and its more probable limits, via use of known rate coefficients and theoretical predictions, is outlined and then applied to the representative monomers, styrene and methyl methacrylate. A detailed application of the theory and illustration of the methodology of model discrimination via experiment is contained in the second article of this series. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320402
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  • 2
    Electronic Resource
    Electronic Resource
    Free radical exit in emulsion polymerization. II. Model discrimination via experiment (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 631-649 
    Details
    ISSN: 0887-624X
    Keywords: free radical ; exit ; emulsion ; polymerization ; experiment ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In emulsion polymerizations, desorption (exit) from latex particles of monomeric radical species that arise from transfer can be an important determinant of the overall kinetics. An examination of various methodologies for the testing of postulated free radical exit mechanisms is made. These utilize the model descriptions for the exit process presented in the accompanying article of Casey et al., employing data consisting of conversion as a function of time for the approach to steady state polymerization conditions. Experimental data are presented on the exit rate coefficients as a function of such experimental parameters as: particle size, monomer concentration, and aqueous-phase free-radical concentration for a series of styrene polymerizations at 50°C, where the average number of free radicals per particle (n̄) never exceeds 0.5. It is demonstrated for these systems that while the conversion/time dependence from a single run, under conditions sensitive to exit, is insensitive to mechanistic assumptions as to the fate of desorbed free radicals, the variation of the exit rate coefficient with particle size so obtained suggests a second order dependence on n̄, implying complete re-entry of desorbed free radicals under all conditions studied. Once the monomeric radicals have re-entered, they are more likely to remain inside the particle where they will either propagate or undergo termination rather than re-escape. The article also presents an estimate for the rate coefficient at 50°C of the first propagation step of the monomeric radical subsequent to transfer. The conclusions drawn here for seeded systems should prove useful for study of particle nucleation mechanisms, when exit is particularly likely in small, newly formed, particles. © 1994 John Wiley & Sons, Inc.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320403
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  • 3
    Electronic Resource
    Electronic Resource
    Radiation-initiated inverse emulsion polymerization of vinylpyrrolidone (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 1385-1390 
    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: The radiation-induced inverse emulsion polyerization of vinylpyrrolidone using an isoparaffinic hydrocarbon and nonionic emulsifier blend is described. High molecular weight polyvinylpyrrolidone (PVP) (1 million to 2 million Mv) was readily obtained at rapid polmerization rates (Rp ∼ 10-35 mol 1-1 s-1) to high conversions (90-95%). The polydispersity of the polymer varied from 2.6 to 4.4, suggesting that chain transfer to the polymer had occurred. Adding a polymeric surfactant to the nonionic blend modified the polymerization rate and particle-size distribution. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070531013
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  • 4
    Electronic Resource
    Electronic Resource
    Free radical synthesis of α,ω-primary amino functionalized polyisoprene through the functional thermal inferter [bis(N-(2-phthalimidoethyl)piperazine)]thiuram disulfide (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 195 (1994), S. 243-251 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The primary amino functional iniferter [bis(N(2-phthalimidoethyl)piperazine)]thiuram disulfide (PEPTD) was synthesied and characterized. Thermal polymerization of isoprene in the presence of the initiator afforded α,ω-functionalized polyisoprene with primary amino end-groups after cleavage of the phthalimido group with butylamine. The kinetics of polymerization of isoprene using this iniferter was studied at 80, 85, 90 and 100°C. Interestingly, isoprene showed a complex kinetic behavior. The different parameters, related to initiation, chain transfer and primary radical termination reactions, as well as the constants for thermal decomposition of the initiator, were determined. From the Arrhenius plot, the activation energy of the overall decomposition constant of PEPTD (2 f kd) was calculated to be 110 kJ/mol. The functionality of the telechelics was examined by GPC.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1994.021950122
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  • 5
    Electronic Resource
    Electronic Resource
    Electron paramagnetic resonance investigation of the nature of the propagating species in methyl methacrylate polymerization (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 195 (1994), S. 3159-3172 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The electron paramagnetic resonance (EPR) spectrum of methyl methacrylate polymerizing in a range of systems is simulated using a consistent set of parameters for two rotamers of a single free radical. The 9-line spectrum observed in bulk and emulsion polymerization was fitted by a superposition of two spectra corresponding to two rotamers of a long-chain species (each a somewhat hindered, non-rotating macroradical), having anisotropic methylene proton hyperfine couplings which can be treated as isotropic to a good approximation. The 13-line spectrum observed at low conversion with very high radical flux was simulated as a superposition of the spectra of two very similar rotamers, the EPR spectra of which are indistinguishable; either rotamer is part of a very short chain (primarily an initiator fragment which has propagated once) undergoing free rotation in a low-viscosity medium. Thus the EPR spectra can be explained without having to invoke earlier suggestions that there are two types of free radicals (“trapped” and “untrapped”) in these systems, corresponding to the 9-line and 13-line spectra. The existence of an enormous proportion of very short free radicals under conditions of high radical flux is supported by quantitative calculations of the radical chain-length distribution. It is suggested that the two rotamers have significantly different propagation rate coefficients because of differences in the hindered rotations in their transition states.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1994.021950914
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis and functional analysis of phenyl-end-blocked poly(methyl methacrylate) with N,N′-dimethyl-N,N′-bis(phenethyl)thiuram disulfide as a thermal iniferter (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 195 (1994), S. 315-327 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Phenyl-end-blocked poly(methyl methacrylate) was synthesized by bulk polymerization of methyl methacrylate by a new functional iniferter, viz., N,N′-dimethyl-N,N-bis(phenethyl)-thiuram disulfide by thermal polymerization. The iniferter was synthesized and characterized by elemental analysis, ultraviolet, infrared, 1H and 13C nuclear magnetic resonance (1H NMR and 13C NMR). Some kinetic parameters like rate of polymerization, variation in the molecular weight and transfer constants as a function of iniferter concentration in the temperature range between 55°C and 100°C have been studied. The rate of polymerization increased with increasing temperature but passed through a maximum with respect to the iniferter concentration. The rate did not follow straight-line behaviour with respect to iniferter concentration as usually found with alkylthiuram disulfides. The chain transfer due to iniferter exhibited the usual temperature dependence, and the activation energy was of the same order of magnitude as for the aliphatic thiuram disulfide. Spectral and thermal analyses of the resultant polymers confirmed the terminal functionalization of the polymer chains.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1994.021950129
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  • 7
    Electronic Resource
    Electronic Resource
    Particle growth in butadiene emulsion polymerization, 2.Part 1: cf.3. Gamma radiolysis (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 195 (1994), S. 635-640 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the emulsion polymerization of butadiene at 60°C in Smith-Ewart interval III were investigated using gamma radiation to produce initiating species. The aim of this work was to determine radical desorption rate coefficients through monitoring non-steady state kinetics. The acquired data of the average number of radicals per particle (n) were in good agreement with data obtained from chemically initiated experiments. It was shown that the approach to steady state is kinetically determined and that thermal background initiation is negligible in the butadiene emulsion polymerization. While radical desorption rate coefficient data was determined with high uncertainty, the results are consistent with the transfer diffusion mechanism of radical exit.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1994.021950220
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