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A new type of ‘intelligent’ hydrogels has been developed in the form of organic/inorganic hybrid materials by making use of the sol‐gel technology. Poly(N‐vinylcaprolactam) (PVCL) has been incorporated in these materials for its thermo‐responsive properties. The synthesis of the hybrid hydrogels was achieved by the in situ formation of an inorganic silica phase in the presence of an aqueous solution of high molecular weight PVCL. This methodology results in the preparation of micro‐heterogeneous systems in which silica particles of nanometer dimensions act as physical cross‐links for the PVCL molecules. Hydrogen bonds between the remaining non‐condensed silanol groups and the PVCL carbonyl functions, together with physical entanglements, are responsible for the strong interactions between the organic and inorganic phases. Stress‐strain tests on highly swollen materials demonstrated that the unique structure of these thermo‐responsive hybrid hydrogels improves the mechanical stability to a great extent as compared to conventional hydrogels. Transmission measurements demonstrate that the presence of the inorganic phase does not influence the cloud point temperatures of PVCL significantly. On the other hand, the response of the reinforced hybrid hydrogels to temperature becomes less pronounced for increasing silica fractions. The reversibility of the swelling/deswelling process has been demonstrated by swelling experiments as a function of temperature. PVCL/SiO2 hybrid hydrogels.magnified imagePVCL/SiO2 hybrid hydrogels.

A new type of thermo‐responsive hydrogels based on the polymer poly(N‐isopropyl acrylamide) (PNIPAA) has been synthesized with the sol‐gel technology. For the preparation of this type of nano‐structured hydrogels, the inorganic silica phase was synthesized by the sol‐gel process in the presence of an aqueous solution of high molecular weight PNIPAA. This combination of the organic and inorganic phases forms hybrid hydrogels with a semi‐IPN morphology. The unique structure of these hydrogels improves the mechanical stability to a great extent as compared to conventional PNIPAA‐hydrogels. This was shown by stress‐strain experiments and the capability to absorb and desorb large amounts of water. The silica only slightly influences the transition temperature of the hydrogels but allows us to vary the thermo‐responsive properties of the materials to a great extent.

Es wird über verschiedene durch Duroplaste ausgelöste Korrosionserscheinungen berichtet. Im ersten Teilbericht wird der Zusammenhang zwischen Formstoffzusammensetzung und Gehalt an korrosiven Bestandteilen dargestellt. Es zeigt sich, daß je nach Harz und Harzträger einzelne dieser Bestandteile wie flüchtige organische Säuren, freies Ammoniak, freies Phenol und Formaldehyd verstärkt auftreten. Ihr Gehalt kann durch eine kurzfristige Wärmebehandlung des ausgehärteten Formstoffes nur wenig beeinflußt werden. Freies Ammoniak in Phenoplasten kann noch nach Jahren in der Atmosphäre abgeschlossener Volumina zu NH3‐Konzentrationen führen, die für andere Werkstoffe kritisch sind. Neben Messing ist vor allem Polycarbonat gefährdet, wobei die Schädigung mit einer Verminderung des mittleren Molekulargewichtes verbunden ist.