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  • 1990-1994  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    A new biodegradable copolymer of glycolic acid and lactones with relatively low molecular weight prepared by direct copolycondensation in the absence of catalysts (1991)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 25 (1991), S. 315-328 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Relatively low-molecular-weight copolyesters of glycolic acid (GA) with lactones such as γ-butyrolactone (BL), δ-valerolactone (VL), and ∊-caprolactone (CL) were synthesized by copolycondensation without catalysts. The resulting copolyesters are intended as carriers for drug delivery systems. Copolyesters with approximately 85 mol% GA (number-average molecular weight (Mn): 2900 ± 100) are crystalline and solid and show a parabolic-type in vivo degradation pattern. The in vivo degradation of amorphous-pasty poly (GA/CL) (approximately 50/50 mol%) changed from parabolic-type to lineartype to S-type pattern as their molecular weight increased. A luteinizing hormonereleasing hormone agonist, D-Leu,6 desGly10 -LHRH ethylamide monoacetate (LHRH agonist), was incorporated into small cylinders with these copolyesters. An initial burst of LHRH agonist was observed for cylinders prepared with parabolic-type degrading copolyesters, in contrast to a marked delay in LHRH agonist release for cylinders prepared with S-type degrading copolyesters. The resulting daily dose of drug was maintained an approximately constant, though decreasing stepwise with time. For example, the daily amount of LHRH agonist released in vivo from a cylinder prepared with poly(GA/CL) (50/50 mol%; Mn = 4500) was 61 ± 39 μg/day throughout an experimental period of 10 weeks with a corresponding pharmacological effect on the rat prostate.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820250304
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of phosphoric acid on the polycondensation of ε-caprolactone with δ-valerolactone and biodegradation of their copolyesters (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1067-1072 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Copolycondensation of ε-caprolactone (CL) and δ-valerolactone (VL) was performed in the presence and absence of phosphoric acid, in order to clarify the competition between the ring-opening reaction of lactones and the polycondensation of linear compounds produced by this reaction. The gel permeation chromatography data showed that the monomer peaks remained in the system even after 7 h from start of the reaction when polymerized in the absence of phosphoric acid and, on the contrary, in the presence of phosphoric acid the peaks disappear perfectly within 1 h. The weight-average molecular weights (M̄w) of poly(CL-co-VL), obtained by copolycondensation with and without phosphoric acid at 200°C for 1 h, were approximately 540 and 8900, suggesting that phosphoric acid markedly accelerates not only the rate of ring-opening but also the rate of copolycondensation. On the other hand, the biodegradation of the copolyesters obtained is characterized by the action of a lipase-type enzyme, showing a typical parabolic-type degradation pattern.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021920505
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    In vivo characteristics of low-molecular-weight copoly(L-lactic acid/DL-hydroxyisocaproic acid) with parabolic-type and S-type degradation pattersn (1990)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 191 (1990), S. 731-736 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An amorphous copolyester of L-lactic acid (LA) and DL-hydroxyisocaproic acid (HICA) with a number-average molecular weight (Mn) of 1600-4800 was synthesized by direct copolycondensation in the absence of catalysts, in order to develop a biodegradable carrier for drug delivery systems. The in vivo degradation pattern was changed into an S-type from a parabolic-type with an increase in molecular weight of copolyester. A luteinizing hormone-releasing hormone agonist, des-Gly10-[D-Leu6]-LH-RH ethylamide, was incorporated into a fine cylindrical copolyester formulation by the so-called melt-pressing technique. When the S-type degradable and releasable copoly(LH/HICA) (70/30 mol-%) formulations with Mn = 2200 were implanted subcutaneously in the back of rats, the most reasonable serum drug level was observed during the first 15 weeks period, keeping constant at approximately 3,5 ng/ml.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1990.021910401
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis and in vitro degradations of low-molecular-weight copolyesters composed of L-lactic acid and aromatic hydroxy acids (1990)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 191 (1990), S. 2077-2082 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: L-lactic acid (LA) was copolycondensed with various aromatic hydroxy acids such as p-hydroxybenzoic acid (HBA), p-hydroxyphenylacetic acid (HPAA), and p-3-(hydroxyphenyl)propionic acid (HPPA) in the absence of catalysts, in order to investigate the copolymerizability and in vitro degradation. The results of 1H NMR spectroscopy and gel permeation chromatography (GPC) showed that the reaction proceeds quantitatively, but the molecular weight of the copolyesters is relatively low. The in vitro degradation pattern of copoly(LA/HPPA) was changed into an S-type from a parabolic-type with increasing HPPA content in the copolyester, in contrast to only parabolic-type for both copoly(LA/HBA) and copoly(LA/HPAA).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1990.021910910
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of degradable terpolymers responding to external stimuli such as pH, ionic strength and temperature (1992)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 193 (1992), S. 715-722 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Degradable copolymers which respond to external stimuli such as pH, ionic strength, and temperature were successfully prepared by direct polycondensation of L-lactic acid (LA), D,L-mandelic acid (MA), and 3-(p-hydroxyphenyl)propionic acid (HPPA) without the use of a catalyst at 200°C by bubbling nitrogen through the solution. The molecular weights of the copolymers obtained were relatively low because of the low polymerizability of MA and HPPA, e. g., number-average molecular weight M̄n ≦ 2100 and weight-average molecular weight M̄w ≦ 4100. Poly{(L-lactic acid)-co-(D,L-mandelic acid)-co-[3-(p-hydroxyphenyl)propionic acid]} (poly(LA/MA/HPPA)) with a composition of the monomeric units (in mol-%) LA:MA:HPPA = 80:10:10 showed rapid degradation after a lag time of 5 h within 48 h from the start of the test, in M/15 phosphate buffer solution (pH 7,2) at 37°C. With increasing pH and temperature, the rate of degradation was markedly accelerated.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1992.021930317
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    Paper (German National Licenses)
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