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  • 1995-1999  (3)
  • molecular weight between crosslinks (Mc)  (2)
  • Brassica napus  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Evaluation of a Statistical Model for the Formation of Poly [Acryloyl Hydroxyethyl Starch] Microspheres (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 475-482 
    Details
    ISSN: 1573-904X
    Keywords: Flory-Rehner model ; dynamic and equilibrium swelling ; molecular weight between crosslinks (Mc) ; degree of derivatization(DD) ; molar ratio (MR)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To characterize the network structure of Poly (Acryloyl Hydroxyethyl Starch) (Ac-HES) microspheres and test the theoretical model and the hypothesis that the rate of swelling of microspheres is inversely related to the extent of crosslinking. Methods. Microspheres were prepared with varying degrees of derivatization (DD) and molar ratios (MR) and subjected to the characterization of matrix structure by dynamic and equilibrium swelling studies utilizing direct microscopic observation and the Flory-Rehner equation. The dependence of average molecular weight between crosslinking Mc, on DD and MR were compared to test the validity of the model. Results. Study of the dependence of Mc on the microspheres preparation parameters, DD and MR, showed that at constant MR, the Mc decreased with DD, while at constant DD, the Mc initially decreased with MR to a minimum, and then increased with MR, complying with the model prediction. Dynamic swelling of microspheres showed a monotonical increase to equilibrium size featured by two time variables, Tp and Teq, that were dependent on Mc; this permitted a conceptual view of the general structure of the Ac-HES microspheres. The Mc, which was more accurately determined by the weight method (as opposed to volume method), was independent of the size of microspheres although there was evidence of variation among particles within a batch. Conclusions. The results validated the model in describing the polymerization/crosslinking reaction of the Ac-HES microsphere system and suggested that Mc is the principal factor in controlling release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012199500072
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Development of a Statistical Model for the Formation of Poly [Acryloyl Hydroxyethyl Starch] Microspheres (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 469-474 
    Details
    ISSN: 1573-904X
    Keywords: poly(Acryloyl Hydroxyethyl Starch) microspheres ; molecular weight between crosslinks (Mc) ; degree of derivatization (DD) ; molar ratio (MR) ; link probability generating function (LPGF)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To develop a mathematical model for predicting the molecular weight between crosslinks, Mc, of poly[Acryloyl Hydroxyethyl Starch] (Ac-HES) microspheres system and to identify and evaluate the key microsphere preparation parameters which affect the Mc of the formed microsphere structure based on the developed model. Methods. Link probability generating functions (LPGFs) based on the classical branching theory were used to derive a model for the calculation of Mc for the Ac-HES system. Based on the developed model, simulation was made to study the effects of the microsphere preparation variables on Mc of the formed microspheres. The process variables were the degree of derivatization (DD) of the Ac-HES, the molar ratio (MR) of the Ac-HES to acrylamide monomer, the fractional conversion of the unsaturation (α), the initiator efficiency (f), the molar concentration of initiator (I), the fraction of intramolecular cyclization (c), and the total weight of the reactable monomer and polymer (s). Results. A model to describe the crosslinking reaction of Ac-HES system and predict Mc was developed. Simulation based on the model showed that Mc decreased as α increased and reached a limiting value before total conversion. At constant α, Mc initially decreased with MR to a minimum and then increased with MR; while Mc decreased monotonically with DD. I and c affected Mc only at very low α and changes in s and f had no effect on Mc. Conclusions. Simulation based on the model suggested that the most important microsphere preparation parameters influencing Mc of the Ac-HES system are the number of functional groups on the Ac-HES (DD) and the stoichiometry (MR) of the crosslinking reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012111116002
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Development of a boron buffered solution culture system for controlled studies of plant boron nutrition (1997)
    Springer
    Plant and soil 188 (1997), S. 21-32 
    Details
    ISSN: 1573-5036
    Keywords: boron ; Brassica napus ; buffered solution ; chelate ; equilibrium ; nutrient solution ; resin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Chelated-buffered nutrient solutions are used for studies on micronutrient metals but so far no equivalent system exists for boron nutrition studies: the present investigation was initiated with that intention. From a literature review, it was noted that a range of substances form chelates with boron including polyhydric alcohols, sugars and phenolic compounds. However, none apart from hydrofluoric acid formed chelates with formation constants comparable to those of micronutrient metal chelates like diethylenetriaminepentaacetic acid (DTPA). Moreover, most chelating substances had deleterious side effects which reduced their possible use in water culture: many of the compounds are substrates for bacterial growth, some are harmful to handle, and others are toxic to plants or humans. Borosilicate glass; was tested in a laboratory experiment but found to release boron too slowly into solution to maintain constant boron concentration in solution even when very finely ground. Current investigations centre around the use of a boron-specific resin, which strongly complexes H3BO3 on its N-methyl glucamine functional groups. The boron sorption capacity of the resin varied from 2.2 to 5.0 mg B g-1 resin. Boron saturated resin maintained an equilibrium solution boron concentration of 46 μt M when added at the rate of 2 g of resin to 1 L of boron free triple deionised water. Plants grown in complete nutrient solution with boron saturated resin added at 1 g per litre of nutrient solution grew as well as plants grown in conventional nutrient solution containing 9.2 μt M boron and their shoots contained adequate boron concentrations for growth. There was no evidence that the resin had effects on plant growth other than in releasing and equilibrating boron concentration in the nutrient solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004291225723
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    Paper (German National Licenses)
    Fulltext
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