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  • 1
    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: Fibers spun from liquid crystalline solutions or melts are characterized by a high degree of chain alignment which promotes high values of tenacity and tensile modulus in the direction of fiber axis but lower values in the transversal direction. Structural modifications are introduced into the flexible moiety and the mesogenic group to alleviate this shortcoming. The incorporation of a spacer based on 2-dodecenedioic acids into a thermotropic liquid crystalline polyester was studied. A phase diagram was established to optimize the composition of such copolyesters. A significant increase in mechanical properties on crosslinking through UV irradiation was observed. A remarkable property of such systems is the retention of molecular chain order in spite of temperatures in excess of Tg. This is valid for both crosslinked and uncrosslinked systems. Remarkable also is the crystallization on annealing of a number of copolymer compositions in spite of a structural difference between the comonomer units.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurde der Einfluß von aliphatischen Estern, Aldehyden und Verunreinigungen, die im Vinylacetat üblicherweise vorhanden sind  -  wie Monovinylacetylen und Divinylacetylen - auf die Polymerisation von Vinylacetat untersucht. Ester und gesättigte aliphatische Aldehyde, wie z. B. Methylacetat, Äthylacetat, Isopropylacetat, Dimethyloxalat usw., Acetaldehyd und Butyraldehyd, wirken nur als Überträger. Ihre Übertragungskonstanten wurden bestimmt. Ungesättigte Aldehyde, wie Crotonaldehyd, aber auch Benzaldehyd, ferner Mono- und Divinylacetylen wirken als Verzögerer. Die Polymerisationsgeschwindigkeit von Vinylacetat in Gegenwart solcher Verzögerer wurde nach der Gleichung von KICE analysiert, und die verschiedenen Geschwindigkeitskonstanten wurden bestimmt.
    Notes: Effects of aliphatic esters, aldehydes and some impurities, as monovinyl and divinyl acetylene which exist normally in vinyl acetate, on the polymerization of vinyl acetate were studied. Esters and saturated aldehydes such as methyl acetate, ethyl acetate, isopropyl acetate and dimethyl oxalate etc. and acetaldehyde and butyraldehyde act only as transfer agent and the values of the transfer constants on these substances were determined. Unsaturated aldehyde such as crotonaldehyde and also benzaldehyde, and monovinyl and divinyl acetylene act as retarder. The several reaction constants relating the retarding effect were obtained.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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