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  • 1
    Electronic Resource
    Electronic Resource
    Direct copolymerization of L-lactic acid with γ-butyrolactone in the absence of catalysts (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 1553-1559 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The copolymerization of L-lactic acid (LA) with γ-butyrolactone (BL), performed without catalyst at 200°C under nitrogen in order to obtain a relatively low-molecular-weight copolymer, proceeds via direct condensation between linear LA and linear 4-hydroxybutyric acid produced by hydrolysis of the cyclic BL. The copolymers were characterized with respect to the copolymerizability (13C NMR spectroscopy), composition (1H NMR spectroscopy), molecular weight (terminal group analysis and gel permeation chromatography), and crystallinity (differential scanning calorimetry). The copolymerizability of BL is low, e. g., the contents of BL units in the copolymers were found to be 12, 16, and 19 mol-% for initial BL contents in the monomer feed of 30, 50, and 70 mol-%, respectively, in which copoly(LA/BL) is composed of blocks of lactyl units separated by single γ-oxybutyryl unit.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900707
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of biodegradable poly(L-lactic acid-co-D,L-mandelic acid) with relatively low molecular weight (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 2407-2415 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A homopolymer of L-lactic acid (LA), which was synthesized by direct polycondensation in the absence of a catalyst at 200°C, is crystalline, in contrast to the homopolymer of D,L-mandelic acid (MA) which is amorphous. Poly(LA-co-MA), obtained under the above conditions, is amorphous over a wide range of composition from 15 to 100 mol-% of monomeric units of MA. The in vitro degradation mechanism of these homopolymers shows a parabola-type degradation pattern for poly(LA) and no degradation throughout an experimental period of 15 weeks for poly(MA). In poly(LA-co-MA) the degradation mechanism leads to a typical S-type degradation pattern, which may be divided into two processes, initial swelling at the surface of the matrix without degradation (induction period), followed by the erosion of oligomers produced by degradation of the main chain in the swollen state.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021901007
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Low-molecular-weight copolymers composed of L-lactic acid and various DL-hydroxy acids as biodegradable carriers (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 2571-2577 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Biodegradable copolymers of L-lactic acid (L-LA) and DL-α-hydroxy acids with relatively low molecular weights, for example L-LA/DL-lactic acid (DL-LA), L-LA/DL-α-hydroxybutyric acid (DL-HBA), L-LA/DL-α-hydroxyisovaleric acid (DL-HIVA), and L-LA/DL-α-hydroxyisocaproic acid (DL-HICA), were synthesized by quantitative direct copolycondensation without catalysts at 200°C. The in vitro degradation, which was evaluated by measuring the weight loss of these copolymers in M/15 phosphate buffer solution (pH 7,2) without enzymes at 37°C, is strongly dependent on the kind and molecular weight of these copolymers, resulting in the formation of different degradation patterns such as parabola type (L-LA/DL-HBA system), linear type (L-LA/DL-LA system), and S type (L-LA/DL-HIVA and L-LA/DL-HICA systems).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021901022
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    Paper (German National Licenses)
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