CONDITIONS OF NUCLEATION IN CRYSTALLIZABLE POLYMERS - RECONNAISSANCE OF POSITIONS - A CRITICAL-EVALUATION

In view of the enormous difficulties in obtaining reliable experimenta l data for the purpose of structure simulation with the aid of compute r programs (presently being so popular), every classifying endeavor mu st be considered of great importance. One of the goals of such an ende avor is the demarcation of characteristic temperature ranges. With the aid of thermodynamic considerations an estimate of the restricted tem perature range of metastable undercooling, in which the classical theo ry of homogeneous nucleation, as developed for polymer solutions, is v alid also for polymer melts (''thermal nucleation'') can be given. Thi s consideration includes a discussion of the course of the relevant in terface tensions along the co-existence lines of the P-T diagram. The so-called spinodal crystallization mode (see [1-3]) is found at lower temperatures and seems to be quite common in polymer crystallization. III this connection the so-called athermal nucleation can be identifie d with a specific process. However, the present author is not in favor of the term ''spinodal mode''. This is explained by a comparison with the meaning of spinodal decomposition into two phases in the ordinary gas-liquid phase transition, which always occurs at the lower bound o f the metastable undercooling. Remarkably, spinodal decomposition cann ot be defined in the same way for the liquid-solid transition. Anyway, the author tries hard to induce unorthodox trains of thought in the h ope to revive the discussion of a difficult matter, which has almost g one to sleep, before a satisfying settlement has been reached.