| Abstract: | The melting process of isotactic poly(propylene) (iPP) sample isothermally crystallized at 130°C for half an hour is carefully studied by means of variable‐temperature FTIR spectroscopy and DSC. Based on the IR intensity changes of regularity and conformational bands vs. temperature, it is found that the helical structure of macromolecular chains can be retained in the iPP melt after the polymer crystals are melted. When temperature is somewhat higher than 170.5°C, the macromolecules get sufficient energy from surroundings to overcome the energy barrier of helical structure, so the quantity of helical structure in iPP melt reduces dramatically. This conclusion is also confirmed by DSC studies on crystallization behavior of different iPP melts. The activation energy to destroy the helical structure of iPP melt is 60.1 kcal/mol determined by the Snyder method. After the major transition, some level of order still persists in the melt and it is gradually lost at higher temperatures. |
