Thermokinetic Properties Research Articles

Thermally stimulated current studies of thermotropic polyesters with polymethylene spacers (I): The glass transition and relaxation behavior of anisotropic and isotropic glasses

AbstractThermally stimulated current (TSC) and relaxation map analysis (RMA) were used to study the glass transitions and relaxation phenomena of the anisotropic and isotropic glasses for the semiflexible polyesters with various polymethylene spacers (n = 7 ˜ 10). TSC analysis indicated that the glass transition temperatures (Tg) of polymers at around 40 ˜ 50°C exhibited an apparent even‐odd behavior not only for the anisotropic glasses but also for the isotropic glasses. The Tg of the isotropic glass for the polymer with even n value was observed to be higher than those for the two neighboring polymers with odd n values. The anisotropic glass for the polymer with even n value had a lower Tg than those for the two neighboring polymers with odd n values. The lower value was attributed to the configuration and orientation effects on the behavior of polarization. RMA revealed that the relaxation modes of the investigated polymers were also influenced by the configuration and orientation effects. The dipolar relaxation of the anisotropic glass for the polymer with odd n value occurred at a higher temperature and had a lower entropy (enthalpy) of activation than that of the isotropic glass for the same polymer due to the orientation effect. However, an inverse relation was found to occur for the polymer with even n value, which came from the trans configuration of the even polymethylene spacers. Finally, the thermokinetic properties evaluated by RMA (e.g., the final state after depolarization) correlated quite well with the results obtained by TSC. © 1995 John Wiley & Sons, Inc.

Thermokinetic properties of inhibited vegetable oils

Castor, corn and linseed oils with the addition of inhibitors were investigated using a DSC equipped with a pressure DSC cell. The inhibitors used in the experiments were 2,6-di- t-butyl-4-methylphenol and propyl gallate. The measurements were carried out under isothermal conditions in an atmosphere of oxygen. Thermal curves from DSC runs permitted the determination of onset and maximum points of the peak which were then compared to those of the pure oils. The apparent activation energies of oxidation of the oils were calculated using the model of the autocatalytic reaction and the Arrhenius equation.

Kinetics of the Fluorination/Chlorination of 1-Chloro-1,2,2,2-Tetrafluoroethane

The kinetics of the catalytic fluorination and chlorination of 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124) by HF and HCl to give pentafluoroethane (HFC-125) and 1,1-dichloro-2,2,-trifluoroethane (HCFC-123), respectively, were examined in order to further define the mechanisms of these reactions. An HF-treated preparation of 2% CoCl2 on Al2O3 was used as a catalyst. Reaction of deuterium-labeled HCFC-124 with HF or HCl showed the deuterium to be retained in both reactant and products. suggesting the absence of carbenoid or olefinic intermediates in these halogenations. Thermodynamic and thermokinetic properties of these halogenations were also determined in order to determine the extent of contributions of reverse reactions to the kinetics of these halogenations. Kinetic studies indicated that these halogenations are consistent with a classical Langmuir-Hinshelwood mechanism where both HX (X = F or Cl) and HCFC-124 are adsorbed on identical active sites of the catalyst in the rate-determining step.

Study on Thermokinetic Properties of Bacterial Growth

Study on Thermokinetic Properties of Bacterial Growth

Genomic integrity of T1 DNA after γ- and ultraviolet irradiation

T1 DNA, γ-irradiated in the phage particle or irradiated with ultraviolet light was checked for structural integrity by kinetics of melting and reannealing. γ-Irradiated DNA differed in all thermokinetic properties by a factor of 3–4 from DNA degraded by mechanical or enzymatical treatments. Ultraviolet irradiation caused much smaller effects than γ-irradiation. Considering the frequency of pyrimidine dimers in relation to the γ-ray induced lesions, strong evidence can be derived, that in addition to single base damages, local denatured regions are produced by γ-irradiation. Such regions, formed possibly by direct absorption of radiation energy in DNA, i.e. by primary ionizations, are associated with base lesions and are passed over during reannealing.