Closing Remarks

Abstract

The field of polymer crystallization is already an old field and, as such, a very extended one. As a consequence, one unfortunately cannot feel competent in all aspects. In fact, one can be impressed by the amount of special work, which has been presented so far. But this is the reason, why one can still feel as a newcomer, even if one has entered the field already 25 years ago for an investigation of structure formation during processing of semicrystalline polymers. Before the author had been engaged by virtue of life in several other areas of polymer science, as there were: regenerated cellulose, flow birefringence of polymers in solution (development of a flawless apparatus as a starting point), single screw extrusion and polymer melt rheology (heat transfer and flow, inauguration of the flow birefringence of polymer melts). This information must serve as an excuse, if he has overlooked some contributions in the field of polymer crystallization. But this is the risk if at almost sixty one gets the idea to start with a new subject. In such a case there remains only one option, namely to promote own ideas without much delay. Of course, an incontestable condition is the conviction that these ideas are essential, original and not yet promoted by others.

One example is the allusion to the strange temperature dependence of the crystallization kinetics of quiescent melts. Nobody has ever expressed openly his surprise about the enormous difference between the equilibrium melting point and the temperature, where the spherulites of such a polymer are melting. Chen et al. [1] have friendly spoken recently of the “demarcation,” as discovered by the present author. This demarcation is illustrated in Fig. 1.3 for iPP. The difference between the equilibrium melting point of the α-crystal-modification and the temperature range, where the spherulites of this modification melt, is more than 40°C. A similar difference has recently been found for iPS by Al-Hussein and Strobl [2]. Also for Form I of iPB-1 such a considerable difference can be expected, as will be shown in the next section. In fact, there is practically no sporadic formation of nuclei within the range of temperatures between the equilibrium melting point and the temperature, where the spherulites melt. The explanation of this fact is quite simple. At the equilibrium melting point the crystals contain the molecules in stretched conformation. This means that also the pertinent nuclei must contain the molecules in their stretched conformation. But this condition is rarely fulfilled in the melt, where the molecules are coiled up. As a consequence, the activation energy for those nuclei is extremely high.