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  • 1
    Electronic Resource
    Electronic Resource
    Anionic dispersion polymerization of 1,4-divinylbenzene (1990)
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 2623-2628 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00212a005
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Cyclization and Reduced Pendant Vinyl Group Reactivity during the Free-Radical Crosslinking Polymerization of 1,4-Divinylbenzene (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 2728-2737 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00112a019
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  • 3
    Electronic Resource
    Electronic Resource
    Size distribution of polymers during the photoinitiated free-radical copolymerization of methyl methacrylate and ethylene glycol dimethacrylate (1996)
    Springer
    Polymer bulletin 37 (1996), S. 207-213 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Photoinitiated methyl methacrylate-ethylene glycol dimethacrylate (MMA/EGDM) copolymerization has been investigated in toluene at a monomer concentration of 35 w/v %. Diphenyl-2,4,6-trimethylbenzoylphosphine oxide (DPTPO) was used as a photoinitiator at 0.3 wt% concentration. Monomer conversions and the size distribution of the polymer molecules were measured as a function of the reaction time up to the onset of macrogelation. Compared to the photoinitiators benzoin or benzoin derivatives, gelation process proceeds at much higher rates in the presence of DPTPO. The size distribution curves obtained by size-exclusion chromatography (SEC) change from monomodal to bimodal distributions as the polymerization proceeds. Strongly bimodal SEC curves were obtained in the close vicinity of the gel point. This finding confirms the coagulation type gelation mechanism of compact primary particles. It also indicates that the present gelation theories cannot describe the structure dependent kinetics of free-radical crosslinking copolymerization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00294123
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of cyclization and electrostatic interactions on the termination rate of macroradicals in free-radical crosslinking copolymerization (1998)
    Springer
    Polymer bulletin 40 (1998), S. 491-498 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Effects of cyclization and ionic group contents on the termination rate of macroradicals formed at zero monomer conversion were investigated. For this purpose, the pregel regime of free-radical methyl methacrylate / ethylene glycol dimethacrylate (MMA/EGDM) and acrylamide / N,N'-methylenebisacrylamide (AAm/BAAm) copolymerization systems was studied by means of the dilatometric technique. To eliminate the chain-length dependent variation of the termination rates, different sets of experiments were carried out each at a fixed monomer and initiator concentration. At low crosslinker contents, the termination rate of zero-conversion macroradicals was enhanced in crosslinking copolymerizations compared to linear polymerization. This is due to the cyclization reactions which reduce the size of the macroradical coils and thus, enhance the termination rates due to the lowering of the thermodynamic excluded volume effect. As the amount of the crosslinker increases, an enhancement in the initial rate of polymerization is observed in all series of experiments, indicating that steric effects on segmental diffusion dominate at high crosslinker contents. The results also indicate a slower rate of termination of ionic macroradicals compared to the non-ionic radicals of the same molecular weight and points the significance of the thermodynamic excluded volume effect on rising the ionic group content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050281
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of cyclization and pendant vinyl group reactivity on the swelling behavior of polyacrylamide gels (1997)
    Springer
    Polymer bulletin 39 (1997), S. 233-239 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. A series of polyacrylamide (PAAm) gels were prepared by free-radical crosslinking copolymerization of acrylamide and N,N′-methylenebis(acrylamide) (BAAm) in water at various crosslinker (BAAm) and chain transfer agent (isopropyl alcohol, IPA) concentrations. It was shown that only 5% of the crosslinker used in the feed forms effective crosslinks in the final hydrogels. At BAAm contents as high as 3 mole%, the equilibrium swelling ratio of the gels in water is independent of the crosslinker content in the feed. This is due to the prevailing multiple crosslinking reactions during the gel formation process. At a fixed crosslinker content, the onset of gelation is shifted towards higher conversions and reaction times as the amount of IPA increases. Addition of IPA in the monomer mixture also increases the equilibrium swelling ratio of PAAm gels. It was shown that the gel crosslinking density increases on rising IPA concentration in the feed due to the increasing rate of intermolecular crosslinking reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050143
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  • 6
    Electronic Resource
    Electronic Resource
    In situ photon transmission technique for monitoring phase separation in real time during gelation (2000)
    Springer
    Polymer bulletin 45 (2000), S. 281-285 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary In situ, real time photon transmission technique was used to monitor the formation of heterogeneities during the free-radical crosslinking polymerization of acrylamide in the presence of N,N'-methylenebis(acrylamide) (BAAm) as a crosslinker. Two different gelation experiments were performed with various BAAm and water contents separately at room temperature. It was observed that the transmitted photon intensity, I tr decreases dramatically at a certain time, in both type of experiments during the gel formation process from interconnected microgels. Decrease in I tr was interpreted in terms of phase separation during gelation. The extent of phase separation was measured depending on the crosslinker content and on the degree of monomer dilution during the gel formation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890070032
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  • 7
    Electronic Resource
    Electronic Resource
    Heterogeneities during the formation of poly(sodium acrylate) hydrogels (1999)
    Springer
    Polymer bulletin 43 (1999), S. 425-431 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary In situ fluorescence and light scattering techniques were used to study the formation of heterogeneities during the free-radical crosslinking polymerization of sodium acrylate (NaAc) in the presence of N,N'-methylene(bisacrylamide) (BAAm) as a crosslinker. Pyranine was used as a fluorescence probe in the experiments. The reactions were carried out at room temperature and at a monomer concentration of 20.6 w/v% in water. It was found that the gel forming system became turbid at the start of the reaction; continuing polymerization and crosslinking reactions turned the opaque gels into slightly opaque and finally transparent gels. Two peaks were observed both in the scattered and emitted light intensities versus the reaction time plots. The first peak corresponds to the formation and growth of the phase separated domains whereas the second peak reflects the macrogelation point in the reaction system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050631
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  • 8
    Electronic Resource
    Electronic Resource
    Macroporous styrene-divinylbenzene copolymers: Formation of stable porous structures during the copolymerization (1998)
    Springer
    Polymer bulletin 41 (1998), S. 379-385 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The variation of the pore structure of styrene-divinylbenzene (S-DVB) copolymer beads depending on the polymerization time was investigated. Macroporous S-DVB copolymer beads with 10 mol % DVB content were prepared in the presence of cyclohexanol as a diluent. It was found that the stable pores in S-DVB copolymers mainly form at an early stage of the copolymerization, i.e., at the gel point. Thus, the early phase separated portions of the network, where the crosslink density is locally high, do not collapse on drying and illustrate the stable part of the porosity of S-DVB copolymers. The number of stable pores does not change much during the whole course of the copolymerization. The maximum porosity first decreases on rising the post-gelation time due to the decreasing degree of dilution of the gel phase. Then, it increases continuously due to the increasing crosslink density of the gel. The pores formed at a later stage of the copolymerization are unstable and they collapse during the drying process. This is due to the lower crosslink density of the network regions forming later.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050377
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  • 9
    Electronic Resource
    Electronic Resource
    The effect of preparation temperature on the swelling behavior of poly (N-isopropylacrylamide) gels (2000)
    Springer
    Polymer bulletin 45 (2000), S. 175-182 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The role of the preparation temperature of poly(N-isopropylacrylamide) (PNIPA) gels on their swelling behavior in water and in aqueous solutions of sodium dodecylbenzenesulfonate was investigated. PNIPA gels were prepared by free-radical crosslinking copolymerization of N-isopropylacrylamide and N,N'-methylene(bis) acrylamide in water at fixed monomer and crosslinker concentrations. The equilibrium swelling ratio of the gels increases first slightly up to about 20°C then rapidly with increasing gel preparation temperature. Magnitude of the collapse transition in water at 34°C becomes larger as the gel preparation temperature increases. Calculations indicate a decrease in the effective crosslink density of PNIPA gels with increasing preparation temperature. The gels prepared at temperatures higher then 20°C were heterogeneous consisting of highly crosslinked regions interconnected by the PNIPA chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890070046
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  • 10
    Electronic Resource
    Electronic Resource
    Pendant vinyl group reactivity during the free-radical copolymerization of methyl methacrylate and ethylene glycol dimethacrylate (1994)
    Springer
    Polymer bulletin 33 (1994), S. 665-672 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Methyl methacrylate-ethylene glycol dimethacrylate (MMA-EGDM) copolymerization has been investigated in toluene at a monomer concentration of 22 w/v %. The kinetic models developed recently along with the experimental conversion curve and gel point data provided the calculation of the average reactivity of pendant vinyl groups. It was found that the pendant vinyl reactivity for intermolecular links is much less than the monomeric vinyl reactivity and it decreases further as the EGDM concentration increases. At 5–15 mol % EGDM, the average pendant reactivity is 1–2 orders of magnitude lower than the monomeric vinyl reactivity. The reduced pendant reactivity is mainly responsible for the shift of the gel point towards higher conversions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296080
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