SYNOPSISThere are few quantitative comparisons in the literature between glass transitions ( Tg) measured by differential scanning calorimetry (DSC) and by dynamic mechanical analysis (DMA). Also, in the case of DMA, two different operational definitions have been used to obtain the glass transition, namely, the loss modulus (F) and damping (tan 6) peak temperatures. We propose a new DMA definition of Tg and demonstrate that it agrees with DSC Tg measurements within k2OC for both thermoplastic polystyrene and thermoset cross-linked acrylic polyurethane films with measurable tan 6 peaks. The glass transitions for a single polystyrene standard and several cross-linked acrylic polyurethane films were measured by DSC. Additionally, E" and tan 6 peak temperatures were measured by DMA as a function of frequency and temperature. Empirically, it was determined that the average of the E" and tan 6 peak temperatures measured at 1 rad/s oscillation frequency corresponds to the glass transition measured by the ASTM El356 DSC test method. I NTRO D U CTlO NThe glass transition (T,) of a polymer can be determined by observing the temperature range over which a significant change takes place in some specific electrical, mechanical, thermal, or other physical property. This temperature range can vary significantly depending on the property chosen for observation and on details of the experimental technique (e.g., heating rate, test frequency). In this study, glass transitions measured by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are compared.In the literature, there are few quantitative comparisons between glass transitions measured by DSC and DMA. In part, quantitative comparisons are difficult because reported results vary with instrument

ABSTRACT:The differential scanning calorimetry glass transition (DSC T g ), measured by ASTM test method E-1356, and the dynamic mechanical analysis glass transition (DMA T g ), measured using a new definition of the DMA T g , generally agree within {4ЊC for a wide variety of commercially available polymers. The DMA T g is defined as the average of EЉ and tan d peak temperatures measured at a 1 rad/s oscillation frequency.

SynopsisThe influence of elemental red phosphorus on the rate of thermal degradation of poly(ethy1ene terephthalate) has been studied in the temperature range of 400" to 500°C in inert and oxidizing atmospheres by means of isothermal thermogravimetric analysis. Addition of red phosphorus is found to reduce the rates of both the pyrolytic and the thermo-oxidative degradation and to increase the amount of residual char. A correlation of pyrolysis rates with oxygen index data has been attempted.

A study was undertaken to compare two computational methods of estimating kinetic parameters from thermoanalytical experiments. Examples illustrating the relationship between reaction complexity and validity of isothermal vs. non-isothermal kinetic analyses will be presented. Thermal decomposition of several compounds was studied both by isothermal and dynamic thermogravimetry (TG). For the isothermal runs, reaction order and activation energy were estimated using established methods. For the dynamic runs, the statistical method of nonlinear least squares was used to estimate all three kinetic parameters of the nth order decomposition reaction and their individual 95% confidence intervals. Both methods assumed Arrhenius temperature dependence.

SynopsisThe reaction of poly(ethy1ene adipate) (PEA) and toluene diisocyanate (TDI) is studied by means of isothermal DSC. The reaction has the stoichiometry of PEAPrDI = 0.5 and a reaction enthalpy of AH = -65.0 kJ/mol hydroxyl group. The kinetic order is unity over a wide range of temperature and composition of the reaction mixture. The temperature dependence of the first-order rate constant yields an apparent activation energy of 61.1 kJ/mol. The kinetic data are accommodated by the following rate law:A mechanism involving a mobile preequilibrium to accommodate the experimental results is proposed.