Determination of the thermodynamic activity of sulfuric acid in the H2SO4-H2O-HCHO system by an indicator method

The ionization of N,N-dimethyl-2,4-dinitroaniline in water-formaldehyde solutions of H₂SO₄ consists in the addition of a H₂SO₄ molecule to an indicator molecule. The logarithm of the indicator ratio for identical molality of the acid in a water-formaldehyde solution and in water varies linearly as a function of the logarithm of the thermodynamic activity of the acid for a molar ratio of free water to methylene glycol >-10. A method is presented for calculation of the thermodynamic activity of the acid in the H₂SO₄,-H₂O-methylene glycol system in the H₂SO₄, molality range from 1 to 4 for the given molar ratio of free water to methylene glycol.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 987–991, May, 1990.     

Kinetic method by using calorimetry to mechanism of epoxy-amine cure reaction

Some specific features of the thermochemistry of epoxy-amine curing at the later stages of the reaction are considered. Possible mechanism of cross-linking and the question about the driving force leading to the infinite network are discussed. The coupling of the reaction kinetics and rearrangement of the chains crosslinked into the rigid supramolecular structure is the essential feature of epoxy-amine vitrified system. It has been proposed that owing to the contribution from the side process, different curing temperatures can result in the structures with different T _g. It was also established that reaction of epoxy ring opening alone is not responsible for the residual curing. The latter is the result of the side processes. As compared with the reaction of epoxy ring opening the side processes are strongly dependent on the geometrical aspects. This revised version was published online in August 2006 with corrections to the Cover Date.