The enthalpies of solution, ∆ sol H m , in water of urea, N-methylurea, N-ethylurea, N-propylurea, N-butylurea, N-isobutylurea, and N-tert-butylurea were measured by isothermal calorimetry at T ) (296.84, 306.89, 316.95) K. The molar enthalpies of solution at infinite dilution, ∆ sol H m ∞ , at T ) 298.15 K were derived and added to the molar enthalpies of sublimation, ∆ sub H°m, at the same temperature to obtain the molar enthalpies of solvation at infinite dilution, ∆ solv H m ∞ . The partial molar heat capacities at infinite dilution at T ) 298.15 K, C p,2 ∞ , were also calculated by the summation of ∆ sol C p,m ∞ , derived from our experimental data, and molar heat capacities, C p,m (cr),of urea and N-alkylureas from the literature. The contribution of the CH 2 group to solvation enthalpy and partial molar heat capacity was -3.3 kJ‚mol -1 and 90.8 J‚K -1 ‚mol -1 , respectively, in very good agreement with data in the literature. Simple additive schemes were used to estimate the average molar enthalpy of solvation and partial molar heat capacity at infinite dilution of the HN-CO-NH functional group. Results are discussed in terms of current models for hydration and hydrogen bond formation for urea and its N-alkyl derivatives in water.

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This article presents a procedure of the activation of halloysite and a method of the synthesis of nucleus-sheath type filler. The effects of the nanoadditives obtained on the thermal properties, flammabilities and fire hazards of peroxide and sulfur vulcanizates of NBR and SBR rubbers, are discussed. Based on the test results obtained by derivatography, oxygen index, FAA microcalorimeter and cone calorimeter, the thermal stability, flammability, and fire hazard of the nanocomposites investigated were determined. The results obtained were interpreted from the point of view of the chemical structure of the diene elastomers investigated, their spatial network structure, and the method of halloysite modification.

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Enthalpies of solution, ∆ sol H m , in water, of some di-, tri-, and tetra-substituted N-alkylureas were measured by isothermal calorimetry at T ) (296.84, 306.89, and 316.95) K. The molar enthalpies of solution at infinite dilution (i.d.), ∆ sol H m ∞ , and molar heat capacity changes for the solution process at i.d., ∆ sol C p,m ∞ , were obtained at T ) 298.15 K. Molar enthalpies of solvation, ∆ solv H m ∞ , and partial molar heat capacities, C p,2 ∞ , at i.d. were then calculated from the molar enthalpies of sublimation or vaporization and molar heat capacities, C p,m , of pure compounds in solid or liquid states, respectively. The methylene group contributions to the enthalpy of solvation was -3.7 kJ • mol -1 for di-and tri-N-alkylureas and -3.2 kJ • mol -1 for tetra-N-alkyureas, whereas the contribution to partial molar heat capacity was 91 J • K -1 • mol -1 and 93 J • K -1 • mol -1 , respectively, in very good agreement with our earlier data for monosubstituted N-alkylureas and the literature data for various homologous series of alkyl-substituted compounds. Contributions of the functional groups of N-alkylureas were derived and compared with our earlier data for mono-N-alkylureas. † Part of the "William A. Wakeham Festschrift".