STRUCTURE FORMATION DURING THE INDUCTION PERIOD OF CRYSTALLIZATION OF POLYMERS

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We have succeeded in visualizing the general image of primary crystal nucleation mechanism of polymers. It has so far been considered that there exists only one mechanism in primary crystal nucleation ; i.e., primary crystal nuclei are formed directly in the melt. Our research project has, however, shown that other mechanisms actually exist as well. Thus, the crystal nucleation occurs in different ways depending on the quenching depth from the melt. When the quenching depth is small or crystallization temperature is high, the usual mechanism works, but when it is large or crystallization temperature is low, microphase separation due to orientational fluctuation of rigid segments occurs first in the system and then crystal nucleation begins. Theoretically there may be two types of microphase separation, binodal and spinodal. Industrially the latter type of microphase separation or the spinodal decomposition (SD) type is more important because it gives an ideal structure of crystalline polymer materials with homogeneous, tough properties. We have succeeded in actually observing such a SD pattern with an optical microscope; the optical micrographic patterns drastically change at around spinodal temperature from spherulitic to spinodal structures. For the SD type we have also found two methods crystallized from the melt and the glass ; industrially the latter is more important. A patent on these results is pending. As more fundamental research by means of small-angle X-ray and light scattering, we proposed a structural formation mechanism during the induction period of crystallization, which consists of three steps, extension of rigid segments, the initial and late stages of SD.