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  • 1
    Digitale Medien
    Digitale Medien
    Biocompatible polymeric systems: Copolymerization of 4-methacryloyloxy-acetanilide with 2-hydroxyethyl-methacrylate (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1023-1030 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Soluble copolymers of 4-methacryloyloxy-acetanilide (M), an acrylic derivative of paracetamol, with 2-hydroxyethyl-methacrylate (H) were prepared by free radical polymerization in DMF solution at 50°C, using 2,2′-azobisisobutyronitrile (AIBN) as initiator. The reactivity ratios of both monomers were determined by the application of conventional linearization methods suggested by Fineman-Ross and Kelen-Tudos. The results obtained make clear that this system copolymerizes at random with the reactivity ratios rm = 2.15 ± 0.05 and rH = 0.90 ± 0.10. The microstructure of copolymer chains is described on the basis of the first order Markov statistics. The copolymer glass transition temperatures were determined calorimetrically and the variation of Tg with the copolymer composition is discussed according to modern methods, considering the sequence distribution of monomeric units along the copolymer chains. Also the Tg of the corresponding homopolymers were determined giving the values of Tg(M) = 471 K and Tg(H) = 358 K.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1991.080290709
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  • 2
    Digitale Medien
    Digitale Medien
    Free-radical homopolymerization and copolymerization of ethyl α-hydroxymethylacrylate in tetrahydrofuran (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2313-2319 
    Details
    ISSN: 0887-624X
    Schlagwort(e): free radical polymerization ; ethylα-hydroxymethylacrylate ; homopolymerization ; copolymerization ; copolymer structure ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ethyl α-hydroxymethylacrylate (EHMA) was polymerized in a 3 mol/L tetrahydrofuran solution at 50°C, using 2-2' azobisisobutyronitrile as initiator. The kinetic behavior indicates a higher polymerization rate for EHMA than for methyl methacrylate (MMA). Copolymerization reaction between MMA and EHMA, under the same experimental conditions, was carried out and values of rMMA = 1.264 and rEHMA = 1.285 were found for the reactivity ratios. The comparison of triad sequences as determined from Bernouillian statistic to those calculated from the experimental spliting of O-methyl and α-methyl 1H-NMR signals of the copolymers confirm the obtained results. © 1992 John Wiley & Sons, Inc.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1992.080301104
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  • 3
    Digitale Medien
    Digitale Medien
    Radical copolymerization of 2-acryloyl thioxanthone with methyl methacrylate (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 967-972 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A novel monomer, 2-acryloyl thioxanthone (TXA), was prepared by reaction of 2-hydroxy thioxanthone with acryloyl chloride. Copolymerization of TXA with methyl methacrylate (MMA) in DMF at 80°C was studied in order to evaluate relative reactivities of these monomers. Values of 1.36 and 0.5 were found for the respective reactivity ratios of MMA and TXA, respectively. The resonance stabilization and polar properties were determined and discussed in terms of spectroscopic data.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1990.080280502
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  • 4
    Digitale Medien
    Digitale Medien
    Racemic leucine separation by hollow-fiber extraction (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 1493-1498 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Racemic leucine can be separated into d- and l-isomers by fractional extraction across microporous hollow fibers. In this extraction, an aqueous solution of the racemate is fed to the lumen of the fibers, and an octanol solution of dodecyl-l-hydroxyproline flows countercurrently outside of the fibers. The interface between feed and extractant is stabilized by filling the pores in the hollow-fiber walls with a cross-linked polyvinylalcohol gel which offers negligible resistance to mass transfer. The extraction with dodecyl-l-hydroxyproline deliberately imitates earlier studies, facilitating comparisons of hollow-fiber extraction with other techniques. The results show that the isomer yield per equipment volume of racemic separation is 100 times greater than that in a continuously rotating extractor, and 1,000 times greater than that in a conventional packed tower.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690381002
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  • 5
    Digitale Medien
    Digitale Medien
    Effect of diffusion on heterogeneous ethylene propylene copolymerization (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1669-1684 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In heterogenous olefin polymerization with Ziegler catalysts, the influence of monomer mass transport in the growing granule on polymer properties has been extensively modeled, but it has not been possible to clearly establish the importance of diffusion experimentally since the multisited nature of most Ziegler catalysts can produce similar effects. In this study, ethylene-propylene copolymers were made with single-sited metallocene catalysts by slurry polymerization in liquid monomers. These copolymers had a relatively narrow molecular weight distribution with a composition distribution (CD) broader than expected for a single-site catalyst. Data analysis indicates that mass-transfer limitations in the polymer particles are the most likely explanation for the observed results. For amorphous copolymers, a diffusion/reaction model could predict CD breadth in good agreement with experimental data, but for semicrystalline polymers the model was inaccurate. We postulate that model inadequacies are due to radial gradients in monomer diffusivity during polymerization which the model does not account for.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690401009
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  • 6
    Digitale Medien
    Digitale Medien
    Fractional extraction with hollow fibers with hydrogel-filled walls (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 855-862 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Extractions using hollow fibers can be faster and more efficient than those in conventional equipment. These advantages, due to the large area per volume possible with fibers, can be compromised by accidental convection through the fibers' pores. When these pores are filled with gels of crosslinked polyvinyl alcohol, convection through the pores is stopped but the overall mass transfer is unaltered. The separations across these gel-filled fiber walls provide excellent yield and purity, especially in the case of fractional extraction.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690370608
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  • 7
    Digitale Medien
    Digitale Medien
    Polydisperse tube diameters compromise multiple open tubular chromatographyw (1993)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 946-953 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: This article demonstrates that even 1% polydispersity in hollow-fiber diameters can increase plate heights by as much as an order of magnitude. The demonstration includes an analytical extension of the Taylor-Aris and the Golay dispersion theories, a numerical solution using the measured polydisperity, and successful predictions of the performance of different hollow-fiber systems over a range of flow rates. All these results show that the effect of polydispersity can dominate column performance, especially in the region where the column efficiency is optimal.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690390604
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  • 8
    Digitale Medien
    Digitale Medien
    The effects of thermomechanical coupling on the cold drawing process of glassy polymers (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1073-1085 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The source and the effects of strain-induced heating on the stress-strain behavior and corresponding cold drawing process of glassy polymers are investigated. The nature of dissipative and stored components of work are discussed where only 50 to 80% of the mechanical work of glassy polymers has been found to be dissipative. This phenomenon is demonstrated to be well-modeled by considering a portion of the work to be stored as strain-induced molecular orientation in the polymer that evokes a back stress tensor. The results of the modeling are found to be consistent with experimental measurements reported in the literature. The constitutive and corresponding heat generation model are used in fully thermomechanically coupled finite element analysis of the cold drawing of glassy polymers. The influence of applied elongation rate on the resulting temperature rise, heat transfer, thermal softening, and fiber geometry are presented, together with a full complement of the deformation field parameters related to the propagating shoulders of the drawn neck.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760321605
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  • 9
    Digitale Medien
    Digitale Medien
    Effect of copolymer composition and conversion on the glass transition of methyl acrylate-methyl methacrylate copolymers (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 1191-1203 
    Details
    ISSN: 0887-6266
    Schlagwort(e): methyl methacrylate-methyl acrylate copolymers ; free radical copolymerization ; low and high conversion ; glass transition temperature ; sequence distribution ; compositional variation of glass transition ; modeling ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The glass transition of methyl methacrylate methyl acrylate copolymers over a wide range of conversion and sequence distribution have been analyzed with the only purpose of predicting the change in the glass transition in copolymers as a function of conversion and consequently of comonomer sequence distribution. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/polb.1994.090320707
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  • 10
    Digitale Medien
    Digitale Medien
    A scanning tunneling microscope study of single crystal polyethylene (1990)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 28 (1990), S. 399-410 
    Details
    ISSN: 0887-6258
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The scanning tunneling microscope has been used to image single crystal polyethylene lamellae coated with thin Au or Cr overlayers. The images show a variety of different morphologies ranging from single crystal lamella resting on atomically flat, highly oriented pyrolitic graphite substrates to large pyramidal structures formed by a multilayer growth process. Small outgrowth structures were observed on the top surface of many individual lamellae and were found to be in registry with the edge of the underlying “seed” lamella. The STM studies show evidence for sectorization of the single crystal lamella as well as plastic deformation of overlapping lamellae involving c-axis slip.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1990.140281302
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