THE ROLE OF STATISTICS OF NORMAL VIBRATIO NS OF MACROMOLECULES IN FRACTURE KINETICS OF ORIENTED POLYMERS

The temperature dependences of tensile strength sigma(T) of oriented p olymers were studied under constant loading rate in the temperature ra nge from 80 K to the melting point. It was found that at certain tempe ratures T(t) and T(b), the deviations from the linear dependence corre sponding to the Zhurkov durability formula occur. In parallel were stu died the dependences of thermal expansion of the contour length of the regular sequences of conformers in macromolecules. It was found that the thermal expansion coefficient of such sequences experiences abrupt change at T(t) and T(b). On the basis of this observation, the deviat ions of sigma(T) from linearity are explained by the transition from t he quantum (Bose) statistics of certain vibrations to the classical Bo ltzmann statistics. The maximum frequencies of molecular vibrations th at predominantly govern the temperature dependence of strength were ca lculated from the experimental values of T(t) and T(b).