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  • Polymer and Materials Science  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 243 (1996), S. 177-187 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wird über die Gleichgewichts-Schmelzpunktsdepression von Polycarbonat aus Bisphenol A (PC) in Mischungen mit Poly-∊-caprolacton (PCL) berichtet. Hierzu wird ein Modell entwickelt, das den gekrümmten Verlauf der gemessenen Hoffman-Weeks-Plots zu erklären vermag. Es berücksichtigt die Konzentrationsinhomogenitäten, die mit fortschreitender Kristallisation an der Kristallwachstumsfront entstehen. Die gelegentlich beobachtete Schmelzpunktsdepression der PCL-Komponente wird diskutiert. Der Flory-Hugginssche Wechselwirkungsparameter wird zu -0,09 berechnet; aus diesem kleinen Wert muß geschlossen werden, daß die Mischungspartner enthalpisch nur schwach wechselwirken. Der merkliche Abfall der Glastemperatur des PC nach Einmischen von PCL bewirkt eine beträchtliche Kristallisation aus der Schmelze; es können PC-Kristallinitätsgrade bis zu 25% erreicht werden.
    Notes: It is reported on the equilibrium melting point depression of polycarbonate from bisphenol A (PC) in its blend with poly-∊-caprolactone (PCL). To this end, a model which explains the bended course of the measured Hoffman-Weeks plots is developed which takes into account the composition changes at the crystal growth front upon progressive crystallization. The occasional melting point depression of the PCL component is discussed. The calculated Flory-Huggins parameter of χ12 ≍ -0.09 indicates only weak enthalpic interactions. The remarkable drop in the glass transition temperature of PC with blending allows PC degrees of crystallinity up to 25% upon crystallization from the melt.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 17 (1996), S. 193-195 
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ethylene was polymerized in toluene using methylalumoxane (MAO) activated rac-(Me2SiOSiMe2)[Ind]2ZrCl2 (1) and rac-(Me2SiOSiMe2)[IndH4]2MtCl2 (Mt = Zr (2); Mt = Ti (3)). All three catalyst systems polymerize ethylene with high activity. The molecular weight of polymer produced with zirconocene (1) was up to a weight-average molecular weight M̄w = 1.1 × 106 at low polymerization temperature (〈20°C) under atmospheric pressure. The titanocene catalyst 3 shows lower activity and produced lower molecular weight polyethylene than zirconocenes 1 and 2. Replacement of aromatic rings in 1 by cyclohexane rings, leading to 2, increases activity and reduces molecular weight. The catalyst systems show a dependency of the activity on temperature.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 1107-1111 
    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 new method for measuring the Poisson's ratio of polymer gels has been proposed and has been experimentally demonstrated. The method is based on different swelling behaviors of free and constrained gels. The Poisson's ratio of polyacrylamide gel, as a function of crosslinker concentration, has been measured using this method and has been found to be sensitive to the amount of polymerization initiator. The results are compared with results determined by other methods. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0021-9304
    Keywords: malignant fibrous histocytoma (MFH) ; caprolactone ; lactic acid ; bioabsorbable polymer ; tumorigenicity ; foreign body sarcoma ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Flat plates made from a copolymer of ε-caprolactone and L-lactide (P-CL-LA) [50:50 (w/w), molecular weight 1.62 × 105; 20 × 10 × 1 mm size] were subcutaneously implanted into 50 young, male Wistar rats (P-CL-LA group). After 24 months the plates had become a mass of small pieces, which were concentrated in an area of 3 × 2 × 1 mm. For comparison, 50 rats were implanted with medical-grade polyethylene plates (PE group) while another set of 50 rats was subjected to the same operation but without an implant (Sham Op group). Tumors arose in 25 rats from the P-CL-LA group: 24 were malignant mesenchymal tumors at the implant sites. In the PE group, tumors appeared in 16 rats (14 at the implant sites and two ectopically). The average tumor latency was 578 ± 84 days in the P-CL-LA group and 452 ± 102 days in the PE group. There was no difference in tumor incidence between the P-CL-LA and PE groups (p 〈 0.05). In the Sham Op group, two malignant tumors appeared over 2 years. Pathologically, these induced tumors arose from the inflammatory cells surrounding the degrading fragments of P-CL-LA within the tissue capsule. This indicates that relatively slowly degrading material can induce malignant tumors at a similarly high rate to nonabsorbable medical grade PE, at least in this animal model. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 475-484, 1998.
    Additional Material: 14 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 5 (1984), S. 507-511 
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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