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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of the thermodynamic compatibility of interpenetrating networks during their synthesis (1988)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 26 (1988), S. 1735-1749 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A thermodynamic analysis of interpenetrating polymer networks (IPNs), at any extent of reaction during their synthesis, is presented for both simultaneous and sequential procedures. A model IPN is assumed to be built up by the independent stepwise homopolymerization of two monomers: a tetrafunctional one, A4, and a trifunctional one, A3. No reaction of copolymerization or grafting is allowed between the two types of polymers. For the case of semi-IPNs, A3 is replaced by A2, i.e., a bifunctional monomer leading to a linear polymer. The free energy of mixing is described by a Flory-Huggins lattice model, whereas the elastic contribution is calculated by assuming affine deformation of an ideal elastic network. Results show that a sequential polymerization gives a more incompatible system (i.e., it enters the metastable region at lower conversions) than a simultaneous polymerization starting from the same monomers. In every case, a semi-IPN is shown to be more compatible than an IPN owing to the fact that the average size of the bifunctional monomer increases less with conversion than the size of the trifunctional monomer. When a sequential polymerization begins from a swollen gel at equilibrium, any increase in the extent of reaction of the solvent monomer will lead to its segregation from the swollen gel. The critical Flory-Huggins interaction parameter provides a simple way to ascertain the possibility of phase separation during a simultaneous polymerization.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1988.090260813
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  • 2
    Electronic Resource
    Electronic Resource
    Glass transition temperature versus conversion relationships for thermosetting polymers (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 85-95 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Owing to enthalpy relaxation, values of the glass transition temperature (Tg) for partially reacted polymers may depend on the thermal history of samples and the heating rate used for measurements. Use of theoretical relations between Tg and the extent of reaction (x) of a thermoset must take this fact into account. The original DiBenedetto equation has been reevaluated as a convenient constitutive equation for expressing Tg versus x. An extension of Couchman's approach for the expression of the compositional variation of Tg enabled us to derive the same functionality as given by the DiBenedetto equation. Thus, the DiBenedetto equation may be regarded as based on entropic considerations applied to a model of the thermosetting polymer consisting of a random mixture of a fully reacted network with the initial monomers in an amount which depends on the particular conversion level. These two equations have been applied with success to different diepoxy-diamine copolymers.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090280107
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  • 3
    Electronic Resource
    Electronic Resource
    Phase separation induced by a chain polymerization: Polysulfone-modified epoxy/anhydride systems (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1349-1359 
    Details
    ISSN: 0887-6266
    Keywords: reaction-induced phase separation ; polysulfone-epoxy blends ; epoxy-anhydride networks ; polysulfone-modified epoxies ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction-induced phase separation in a blend of a commercial polysulfone (PSu) with diepoxide-cyclic anhydride monomers, was studied. The diepoxide was based on diglycidylether of bisphenol A (DGEBA) and the hardener was methyl tetrahydrophthalic anhydride (MTHPA), used in stoichiometric proportion. Benzyldimethylamine (BDMA) was used as initiator. PSu had no influence on the polymerization kinetics, the gel conversion, and the overall heat of reaction per epoxy equivalent. A kinetic model including initiation, propagation, and termination steps was used to estimate the distribution of linear and branched species in the first stages of the chain-wise copolymerization. This distribution, together with the PSu distribution, were taken into account in a thermodynamic model of the blend. The interaction parameter was fitted from experimental determinations of conversions at the start of phase separation, obtained under different conditions. The thermodynamic model was used to explain the complex morphologies developed in materials containing different PSu concentrations as well as their dynamic mechanical response. The shift in glass transition temperatures was explained by the fractionation of different species during the phase separation process. Phase inversion produced a significant decrease of the elastic modulus in the glassy state and a thermoplastic-like behavior of the material in the rubbery region. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1349-1359, 1998
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Thermodynamic analysis of the phase separation in polyetherimide-modified epoxies (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 349-356 
    Details
    ISSN: 0887-6266
    Keywords: phase separation ; thermoplastic-modified epoxies ; polyetherimide-modified epoxies ; Flory-Huggins equation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The miscibility of polyetherimides (PEIs) with epoxy monomers based on diglycidylether of bisphenol-A (DGEBA), and with reactive mixtures based on stoichiometric amounts of DGEBA and an aromatic diamine (DA) {either 4,4′-diaminodiphenylsulfone (DDS) or 4,4′-methylenebis[3-chloro 2,6-diethylaniline] (MCDEA)}; was experimentally studied. Cloud-point curves (temperature vs. composition) are reported for PEI-DGEBA and PEI-DGEBA-DA initial mixtures. Cloud-point conversions are reported for the reactive mixtures, for various PEI amounts and polycondensation temperatures. A thermodynamic model based on the Flory-Huggins-Staverman approach, taking polydispersity of both components into account, was used to analyze the experimental information. A single relationship between the interaction parameter and temperature, χ(T), could fit experimental results of mixtures of two commercial PEIs with DGEBA. The addition of DDS led to a decrease in miscibility whereas MCDEA improved the initial miscibility. In both cases, the interaction parameter decreased with conversion, meaning that PEI was more compatible with oligomeric species than with the mixture of starting monomers. The phase separation process in initially miscible rubber- or thermoplastic-modified thermosetting polymers is the result of two factors: increase in the average molar size of the thermosetting oligomer (main driving force favoring demixing), and variation of the interaction parameter with conversion, which may act to increase or decrease the cloud-point conversion determined by the first factor. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    The glass transition temperature of nonstoichiometric epoxy-amine networks (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 1503-1511 
    Details
    ISSN: 0887-6266
    Keywords: glass transition of non-stoichiometric epoxy/amine networks ; epoxy/amine non-stoichiometric networks, Tg of ; networks of non-stoichiometric epoxy/lamine, Tg of ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Glass transition temperatures (Tg) of nonstoichiometric epoxy-amine networks based on the diglycidylether of bisphenol A (DGEBA), are analyzed in terms of the network structure. In most cases reasonable predictions of Tg can be made using an empirical equation reported by L. E. Nielsen together with the experimental Tg value of the stoichiometric network and statistical calculations of the concentration of elastic chains. It is stated that in these rigid networks the concentration of elastic chains is the main structural factor associated to the variations of Tg with stoichiometry. For flexible networks based on the diglycidylether of butanediol (DGEBD), the effect of elastic chains on the Tg value is much less significant.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1991.090291207
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  • 6
    Electronic Resource
    Electronic Resource
    Rubber-modified epoxies. III. Analysis of experimental trends through a phase separation model (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 717-735 
    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: A phase separation model was used to simulate the morphologies obtained in a system consisting of a diepoxide based on bisphenol-A diglycidylether cured with a cycloaliphatic diamine, in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN). A detailed analysis of experimental factors affecting resulting morphologies was previously reported. The model, based on a thermodynamic description through a Flory-Huggins equation, and constitutive equations for polymerization and phase separation rates, could explain most of the observed trends. A nucleation-growth mechanism was believed to take place because of the very low values of interfacial tensions for this type of systems. Conditions which would lead to spinodal demixing are also discussed.
    Additional Material: 27 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1991.070420316
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  • 7
    Electronic Resource
    Electronic Resource
    Citric acid-diethylenetriamine salts as latent curing agents for epoxy resins (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 607-610 
    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: Citric acid (CA)-diethylenetriamine (DETA) salts (CADETA) were prepared by using a 4.5 : 1 molar ratio of DETA-CA and removing the DETA excess. The structure of CADETA was analyzed by 13C-NMR, IR, and DSC associated with weight loss. One-step formulations consisted on dispersions of CADETA (variable amounts) in an epoxy resin based on diglycidylether of bisphenol A (DGEBA, EEW = 185.5 g/eq). The cure was followed in the pressure cell of a DSC (N2 at 2.5 MPa), to avoid volatilization of DETA in the temperature range where decomposition of CADETA and beginning of reaction took place (T 〉 175°C). A very small heat of reaction was observed, (-ΔH) ∼ 10 kJ/eq, resulting from the simultaneous endothermic salt decomposition and exothermic network formation. A stoichiometric formulation showed a Tg = 180°C, i.e., some 60°C higher than the one observed for the usual DGEBA/DETA system.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070450407
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  • 8
    Electronic Resource
    Electronic Resource
    Cure of epoxy novolacs with aromatic diamines. I. Vitrification, gelation, and reaction kinetics (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 1361-1371 
    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 cure reaction of a commercial epoxidized novolac with 4,4' diaminodiphenylsulfone (DDS) was studied at constant cure temperatures in the range 120-270°C, as well as at constant heating rates (differential scanning calorimetry, DSC). Stoichiometric formulations did not attain complete conversion due to the presence of topological restrictions. The limiting conversion was xmax = 0.8. Samples containing an amine excess (≥ 20%) could be completely reacted, whereas this was not possible for formulations containing an epoxy excess. Samples containing a 20% amine excess showed the maximum value of the glass transition temperature (Tg230°C). Cure took place by epoxy-amine hydrogen reactions catalyzed by (OH) groups. A reactivity ratio of secondary to primary amine hydrogens equal to 0.2 was found. The activation energy was E = 61 kJ/mol, as arising from Tg versus time shift factors and time to gel measurements. A unique relationship between Tg and x could be obtained. Gelation took place at xgel = 0.45 and the maximum Tg for the stoichiometric system was Tgmax = 215°C for x = 0.8. A conversion versus temperature transformation diagram was used to represent conditions where gelation, vitrification, degradation, and topological limitations took place. © 1993 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070470806
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  • 9
    Electronic Resource
    Electronic Resource
    The cure of epoxy novolacs with aromatic diamines. II. Statistical parameters of the resulting networks (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 1373-1379 
    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 buildup of the network arising from the reaction of an epoxy novolac (derived from a phenol - formaldehyde novolac resin), with 4,4'diaminodiphenylsulfone (DDS), was modeled using a kinetic-statistical procedure that takes into account (i) the complex structure of the starting novolac, (ii) the actual polymerization kinetics including the different reactivity of primary and secondary amine hydrogens, and (iii) the formation of intramolecular cycles. Predictions of gel conversion and sol fraction were in excellent agreement with experimental results. Glass transition temperatures Tg's of networks prepared at different stoichiometries were predicted using Nielsen's equation (J. Macromol. Sci.-Rev. Macromol. Chem., C3, 69, 1969) and the concentration of elastic chains arising from the model. Theoretical predictions explained the presence of a maximum in the experimental Tg for formulations containing a 20% amine excess. Experimental values of Tg as a function of conversion, for stoichiometric samples, were correlated using a model proposed in the literature. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070470807
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  • 10
    Electronic Resource
    Electronic Resource
    Curing of epoxy resins with in situ-generated substituted ureas (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 39 (1990), S. 383-394 
    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: An epoxy resin based on bisphenol-A diglycidylether (DGEBA) was cured with a substituted urea generated in situ from the reaction of piperidine with an equivalent amount of toluenediisocyanate (TDI). Curing at 100°C or higher temperatures, during 24 h, led to a complete conversion of epoxy groups and the appearance of aliphatic ethers and oxazolidone rings as revealed by IR spectra. The epoxy conversion was proportional to the oxazolidone concentration. The reaction heat was (-ΔH) = 61 kJ/eq. The maximum Tg was 102°C, e.g., the same value as the one obtained with piperidine alone. Thus, the cure with the substituted urea leads to a similar network but has the following advantages: increase in the latency of the initial formulation, absence of secondary amine volatilization (reproducible curing schedule), and decrease in the reaction heat per epoxy equivalent.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1990.070390215
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