Kinetic schemes allowing to interprete the results of high-temperature gravimetric analysis of linear polymers are proposed. A thermoanalytical method has been developed in which the time for establishing constant temperature in the sample is reduced by 1-2 s. The method can be used to determine to what temperature the polymer can be overheated. Kinetics of high-temperature depolymerizationEarlier, by thermoanalytical methods [1] the limit of the temperature interval of polymer thermolysis has been determined "from above", by the characteristic limit temperatures in the range close to the spinoidal point. The relationship between the limit temperatures T t and the weakening of intermolecular interaction has been established: T l = DI/R, where D i is the energy of the intermolecular bonds. However, kinetic relations have not been taken into consideration.We will demonstrate that in the high-temperature range, the depolymerization process taking place in the total volume of the substance (end-group reaction) largely depends on the destruction rate of associated and non-associated monomeric units. We will assume that in each monomeric unit one reaction center exists, and the rate constants of the destruction of associated monomeric units k a and of non-associated (isolated) monomeric units kl are independent of the length ~ of the chain. At uniform distribution of the chains in the volume of the polymer, the kinetics of thermolysis are governed by the equaton -dC/dt = kaN. + kiN,

Experimental and theoretical foundations are established for the limiting temperatures of thermal decomposition of thermoplastic polymers. The correlation between the limiting temperatures and the intermolecular interactions of the polymers investigated is reported.Experimental study of the kinetics of thermal decomposition. It was found earlier by TG and DTA methods that when the heating rate is increased up to some degrees per second, the thermoanalytical curves of polymers, shifted into the high-temperature region, assume extreme positions [1]. The limiting temperatures T/above which the initial materials no longer exist independently of the heating rate were determined. In this paper it will be demonstrated that above finding is valid for even higher heating rates too exceeding 103 deg/s. ExperimentalTo raise the heating rate, contact heaters made of high thermal conductivity metal were applied. The experiments were carried out in the following manner. The metal plate was heated to a constant temperature controlled by a steady-state potentiometer with an accuracy of + 6 ~ The substance to be studied was applied onto the surface of the plate as a thin layer of its melt. At film thicknesses of around 5 Ixm, the sample is clearly observable in reflected light. The heating time tn for a melt film of this thickness to attain the temperature T2 of the plate did not exceed 0.01 s, corresponding at T2 = 500 ~ (793 K) to an average heating rate of b = T/tn = 5.104 deg/s.

A new technique is presented for study of the thermal beha,viour of materials. Experimental and theoretical bases are established for the limiting temperatures of thermal decomposition of different polymers.