The swelling ability of several amphotheric ion exchangers synthesized on the basis of a styrene copolymer with 0.8 % of divinylbenzene can be considerably increased when the original copolymer is subjected to an additional cross-linking process in the swollen state. Isoporous macronet polystyrene often displays a swelling capacity (in poorely solvating media) rising in line with the growing degree of cross-linking. These unusual facts are explained in terms of the influence of cross-linking bridges on the energy of interaction between the polymeric chains and therefore on the energy of the three-dimensional network.
ZUSAMMENFASSUNG:Das Quellungsvermogen verschiedener amphoterer Ionenaustauscher, synthetisiert auf der Basis eines Copolymeren aus Styrol und 0.8 % Divinylbenzol, kann bedeutend erhoht werden, wenn das Ausgangscopolymere einer zusatzlichen Vernetzung im gequollenen Zustand unterworfen wird. Das isoporose makrovernetzte Polystyrol zeigt oft steigendes Quellungsvermogen in verschiedenen schwach solvatisierenden Medien, wenn der Vernetzungsgrad des Grundgerustes erhoht wird. Diese ungewohnlichen Tatsachen werden erklart im Rahmen des Einflusses der Vernetzungsbrucken auf die Wechselwirkung zwischen den Polymerketten und folglich auf die Energie des ganzen dreidimensionalen polymeren Gitters.
Rheological properties of the cryogels produced by freezing of concentrated aqueous solutions of poly(vinyl alcohol) have been studied. These properties were shown to depend on the polymer concentration in the initial solution, on PVA molecular weight, cryostructurization duration and temperature. Electron microscopy demonstrates the heterogeneous porous structure of these cryogels and the dependence of the observed pattern on the conditions of formation of the studied objects.
The influence of the freezing procedure of the solution of initial reactants (aerylamide, N,N'-methylene-bis-acrylamide, radical polymerization initiator) on the dynamics of gel formation and on the properties of the obtained cryogels was investigated. The quenching technique which consists in rapid deep freezing with following heating of the reaction mixture to the preassigned cryosynthesis temperature, results in another macrostructure of the cryogel and differences in the dynamics of gel formation as compared with the usual one-step freezing method.
Untersuchung der Cryostrukturierung von Polymersystemen. V I I I . Besonderheiten der Bildung von vernetzten Poly(acy1amid)-Cryogelen bei unterschiedlichen thermischen BedingungenDer EinfluS des Gefrierregimes der Losung der Ausgangssubstanzen (Acrylamid, N,N'-Methylen-his-acrylamid, radikalischer Initiator) auf die Dynamik der Gelbildung und auf die Eigenschaften der erhaltenen Cryogele wurde untersueht. Die Abschreckmethode, die im schnellen Abkuhlen auf tiefe Temperaturen mit nachfolgender Erwarmung auf die festgelegte Temperatur der Cryosynthese besteht,, ergibt im Vergleieh zum uhlichen einstufigen Gefrierverfahren eine geanderte Makrostruktur der Cryogele und eine unterschiedliche Dynamik der Gelbildung. LOZINSKY, MOROZOVA et al. : Study of cryostructurization of polymer systems. VIII A a a Polymoriu 40 (1989) Nr. 1 9 LOZINSKY, MOROZOVA et a]. : Study of cryostructurization of polymer systems. VIII 90 % 70 50 Act. Polymcria 40 (0989) Nr. 1
The influence of freezing of a reaction mass on the properties of the resulting covalently cross-linked gels is exemplified by a system composed of a solution of chitosan in aqueous acetic acid and glutaric dialdehyde serving as a cross-linking agent. The freezing is shown to lead to a noticeable decrease of critical concentration of gelation as compared with the reactions of polymeric chain cross-linking in ordinary conditions. Consideration is given to some properties of three-dimensional networks obtained by cryostructurization.
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