NATURE OF THE THERMAL STABILITY OF POLYHETEROARYLENES.

The dependence between structure and thermal stability of polyheteroarylenes has been examined. It has been shown that the thermal stability of polymers depends on the two basic factors - an energy factor, determined by the breaking energy of skeletal bonds in The polymer chain, and an entropy factor, which characterizes the probability of effecting the elementary acts of chemical reactions and is expressed via the mobility of the macromolecules. Symmetry of the monomeric units in a chain, regularity in the macromolecules, the absence of bulky substituents, and a high degree of crystallinity aid in reducing the molecular mobility of heterocycloaromatic polymers and in increasing their thermal stability. Analysis of the factors which aid in thermal stability has made it possible to arrive at the conclusion that the polymer glass transition point or melting point can serve as a criterion of the thermal stability of polyheteroarylenes.