Interaction of water with the regenerated cellulose membrane studied by DSC

One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation processes. A large amount of non-freezable strongly bounded water was also detected. Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module at 90°C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected during the first, the second and the third heating. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solvates of Indomethacin

Indomethacin is known to exhibit polymorphism and solvates, the different forms obtained do not exhibit the same solubility and their bioavailabilities are different. It is of a prime importance to identify the various polymorphic and solvated forms. This study was carried out by: DSC (different scanning calorimetry), TG (thermogravimetric analysis), X-ray diffraction and thermomicroscopy. Seven solvates, with acetone, benzene, dichloromethane, tetrahydrofurane, propanol, chloroform and diethylether, were isolated and studied. Their formulae have been determined by thermogravimetric analysis and their X-ray patterns on powder are presented, by DSC their behaviour after desolvation is recorded, the temperature and the enthalpy of fusion are measured and by this way the form obtained is deduced. This revised version was published online in July 2006 with corrections to the Cover Date.     

Macrocycle opening in crown ethers

Macrocycle opening in derivatives of benzocrown ethers under the action of amines is affected by the nature of the heteroatoms in the macrocycle, the nature of the functional group in the benzene ring of the crown ether, and the length, branching, and number of hydrocarbon radicals at the amine nitrogen atom. A distinguishing feature of this reaction is the template effect of MeNH₃ ⁺, Me₂NH₂ ⁺, Na⁺, and K⁺ ions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 687–692, March, 1996.For Part I see Ref. 1.     

Macrocycle opening in formyl derivatives of benzocrown ethers under the action of methylamine

A new method for synthesizing nitrogen-containing podands by nucleophilic regioselective cleavage of the macrocycle in formyl derivatives of benzocrown ethers by heating with methylamine and methylammonium chloride has been developed. This reaction is the first example of crown ether opening by a nitrogen-containing nucleophile.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 950–953, May, 1995.     

Conductance of potassium halides near the temperature of maximum density of water

The conductances of dilute aqueous solutions of KCl, KBr, and KI have been measured over the temperature range 2 to 8°C and have been analyzed by the Fuoss-Hsia equation. The ionic Walden products at infinite dilution have been discussed in terms of local viscosity. The temperature dependence of these products suggest that near the temperature of maximum density of water, the structure-breaking ability of these ions changes in a regular way.     

Light induced refractive index changes in PMMA films doped with styrene

Solutions of poly(methyl methacrylate) in styrene are used to produce thin polymer films (1m–20m) saturated with styrene monomer. In the illuminated areas refractive index changes up to 10^–2 are achieved by photoinduced polymerisation. The index patterns may be fixed by annealing treatments removing the residual monomer.We thank P. Hertel, M. Kopietz, M. D. Lechner and D. Steinmeier for valuable discussions. Financial support of the Stiftung Volkswagenwerk is gratefully acknowledged.     

The influence of hydroxyapatite modification on the cross-linking of polydimethylsiloxane/HAp composites

Hydroxyapatite (HAp) was modified by the action of various hydrophobic agents based on silicon-containing compounds. The influence of the type of applied agent on the thermodynamic and kinetic parameters of the cross-linking of poly(dimethyl siloxane)/HAp composites was investigated. All the modified HAp particles became hydrophobic and these samples were used to synthesize the polysiloxane/hydroxyapatite composites (PDMS/HAp). The possible modes of interaction between the hydroxyapatite and hydrophobing agents were discussed. The most probable interaction between hydroxyapatite and the applied hydrophobing agents is hydrogen bonding. PDMS/HAp composites were formed directly in the cell of the DSC and cross-linking was investigated in situ. It was determined that the introduction of hydroxyapatite into polysiloxane matrices changed the enthalpy of cross-linking, as well as the activation energy of cross-linking and reaction order, while the introduction of modified HAp led to thermodynamic and kinetic parameters more similar to those of the cross-linking of unfilled elastomer.