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  • 1
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 839-848 
    ISSN: 0887-624X
    Schlagwort(e): hyperbranched polyurethanes ; carbonyl azide ; pendant mesogens ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Hyperbranched polyurethanes, with varying oligoethyleneoxy spacer segments between the branching points, have been synthesized by a one-pot approach starting from the appropriately designed carbonyl azide that incorporates the different spacer segments. The structures of monomers and polymers were confirmed by IR and 1H-NMR spectroscopy. The solution viscosity of the polymers suggested that they were of reasonably high molecular weight. Reversal of terminal functional groups was achieved by preparing the appropriate monohydroxy dicarbonyl azide monomer. The large number of terminal isocyanate groups at the chain ends of such hyperbranched macromolecules caused them to crosslink prior to its isolation. However, carrying out the polymerization in the presence of 1 equiv of a capping agent, such as an alcohol, resulted in soluble polymers with carbamate chain ends. Using a biphenyl-containing alcohol as a capping agent, we have also prepared novel hyperbranched polyurethanes with pendant mesogenic segments. These mesogen-containing polyurethanes, however, did not exhibit liquid crystallinity probably due to the wholly aromatic rigid polymer backbone. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 187-215 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The steady state approximation in free radical polymerization is known to break down during the operation of commercial reactors, in which case the unsteady mole balance of polymer radicals have to be solved numerically. We observed that the differential equations governing the zeroth, first, and second moments of polymer radicals in free radical polymerization are nonlinear in nature. The numerical solution of these is “stiff” because the concentration of polymer radicals is very small. Assuming an isothermal reactor, in the absence of the gel effect, these differential equations can be transformed in a suitable new domain where they are linear and can be solved analytically. We have subsequently developed a computer program for nonisothermal reactors in the presence of the gel effect using the analytical solution between any time increment. The results have been compared with those obtained from the fourth order Runge-Kutta technique. We show that when the temperature changes are fast, the Runge-Kutta technique cannot handle the stiffness, and the results begin to deviate from the exact solution. We find that our computer program is computationally efficient in handling this stiffness, takes considerably less time, and can be adapted to any personal computer.
    Zusätzliches Material: 22 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 49 (1993), S. 1309-1329 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: To carry out dispersion polymerization of methyl methacrylate (MMA) in petrol, we have used a poly(MMA) grafted-poly(12-hydroxystearic acid) copolymer as the stabilizer. This special copolymer was prepared as a solution in a mixture of ethyl acetate and butyl acetate solvents. We investigated the effect of graft chain length of the stabilizer on the dispersion polymerization in petrol. We synthesized the stabilizer copolymer with n = 1-4 and determined the rate and the molecular weight of the PMMA formed. There is no dispersion polymerization for n = 1. However, for any other n, for a given stabilizer concentration, as the chain length of the graft is increased, the molecular weight as well as the rate of PMMA formation increases. As opposed to this for a given graft length as the concentration of the stabilizer increases, the molecular weight of PMMA first rises, but for a larger concentration, it begins to fall after undergoing a maximum. In this work, we modeled the heterogeneity of the reaction mass and proposed a mathematical model for dispersion polymerization of MMA in petrol. The computer results are found to conform to the experimentally observed molecular weight of the PMMA. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 1865-1876 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Anionic polymerization with unequal reactivity in batch reactors is a nonlinear problem, and in order to determine the rate constants using the experimental molecular weight distribution (MWD) and conversion vs. time of polymerization, the simulation equations need to be solved repeatedly. In this work, we evolved an efficient algorithm in which the experimental MWD yields the reactivity ratio directly while conversion data give the values of all rate constants. For doing this, we proposed a series solution for the reacting species in terms of monomer conversion. A technique similar to the finite element method for boundary problems is used to divide the conversion into subdomains. The size of these steps is decided by a convergence criterion and results were determined at the end of the conversion domain through sequential computation. The scheme can be implemented on a personal computer and is considerably faster and more efficient. We used experimental data from the literature and demonstrated our technique of evaluating the rate constants. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 41 (1990), S. 2077-2094 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: We have developed an analytical solution of reversible step growth polymerization in semibatch reactor with condensation product flashing. We have shown that the MWD of the polymer formed has Flory distribution, unaffected by flashing of condensation product, if the feed to the reactor is either pure monomer or has most probable MWD. We have determined analytical expression for the time when the evaporation of condensation product starts. Assuming the vapor liquid equilibrium (VLE) is given by Raoult's law (as well as the Flory-Huggins relation) we have determined the number and weight average chain lengths. We have subsequently analyzed the polycondensation step of the formation of polyethylene terephthalate and determined the effect of temperature and pressure on the course of polymerization.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 27 (1982), S. 1217-1231 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Three simplified models of polycondensation reactors are considered in which the condensation product is continuously removed by application of vacuum. Reversible polycondensation reactions of monomers violating the equal reactivity hypothesis have been simulated in these reactors. The effect of various rate and reactor design variables on the molecular weight distribution (MWD) and its moments is studed. It is observed that when the reverse reactions are rapid, the results are fairly sensitive to the level of vacuum applied and to the mass transfer resistance; whereas when the forward reactions predominate, results lie very close to earlier plots for the corresponding irreversible polymerizations. These reactor variables then have relatively small influence on the MWD. Splitting of the MWD curves for odd and even values on n is observed under certain conditions, the effects being more pronounced in the presence of mass transfer than in its absence.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 27 (1982), S. 1759-1769 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Experimental data of Ogata1 has been curve-fitted to obtain the forward and reverse rate constants for nylon-66 polymerization. Its molecular weight distribution (MWD) has been simulated in homogeneous continuous-flow stirred tank reactors (HCSTR) for 11 h of residence time when the reaction mass is very close to equilibrium. The set of algebraic equations have been solved using Brown's algorithm,2 which was found to be more efficient compared to the Gauss-Jordon techniques of solution. The MWD thus obtained is compared with our earlier simulation of the molecular weight distribution from batch reactors3 and was found to differ significantly. In HCSTR, the weight fraction distribution does not undergo a maximum and the polydispersity index ρ of the polymer formed is much higher than that obtained from batch reactors. The number and weight average of the polymer formed in HCSTR is found to be significantly lower.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 27 (1982), S. 3089-3101 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A three-stage isothermal nylon 6 reactor with a kinetic scheme incorporating ring opening, polycondensation, polyaddition, cyclic dimer formation, and reaction with monofunctional acids has been modeled. In the first and third stages, removal of the condensation by-product, water, is prevented. The second stage of this sequence, however, involves finite rates of diffusion of water to cocurrently flowing inert gas bubbles. the number-average chain length of the polymer obtained in this reactor differs substantially from that obtained assuming instantaneous water removal and is a function of the various design variables. It is observed that several choices of these design variables can be made to obtain the same product, thus emphasizing the need for more comprehensive optimization studies than hitherto carried out.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 28 (1983), S. 1063-1076 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Wiped-film reactors carrying out AA + B′B″ type reversible polycondensations (where A, B′, and B” are functional groups, with B′ and B” reacting with A at different rates) have been simulated. The governing mass balance equations have been solved for two transport models of this reactor (one by Ault and Mellichamp and the other by Amon and Denson) using a combination of finite difference and the Runge-Kutta methods. The increase in the number-average chain length μn of the polymer formed in the reactor is computed as a function of the various rate constants and the parameters characterizing the reactor. μn is found to be most sensitive to the surface area of the film and to the temperature used, both for the equal reactivity as well as for the unequal reactivity cases. For the latter, the effect of the reactivity ratio for the forward rate constants is more significant than that of the equilibrium constants. Results of the two models are also compared under similar conditions and it is found that under equivalent conditions, the Amon-Denson model gives slightly higher μn than the Ault-Mellichamp model.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 28 (1983), S. 2261-2279 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Optimal temperature profiles for nylon 6 polymerization in plug-flow reactors have been obtained under different conditions using a reasonable objective function which gives more flexibility to a designer than those studied earlier. Computations suggest that the temperatures at the feed end of the reactor must be maintained at the highest permissible level (determined by the boiling point of the ∊-caprolactam) so as to force the degree of polymerization rapidly to the desired value. Thereafter, the temperatures should be reduced in order to minimize the undesirable cyclic dimer concentration, and, finally, near the exit of the reactor, the temperature must once again be increased in order to attain higher monomer conversion. The effect of a systematic change of values of the various design variables, one by one, is studied. The profile obtained differs substantially from those obtained by earlier workers because of the difference in the objective function as well as in the kinetic mechanism associated with the formation of the cyclic oligomer. Attempts are also made to obtain a global optimal scheme to produce a polymer of a desired degree of polymerization.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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