The introduction of concept of the three domains of isotactic polypropylene (iPP) by Wittmann and Lotz

et al.

is an important advance in understanding the influence of the melt structures on the crystallization behaviors and consequent properties. To further understand the physical nature of the melt structures

the crystalline structures of iPP after thermal treatment in the three domains are systematically investigated. It is found that after treated at different domains the crystal morphologies

including the sizes and birefringence of spherulitic

the proportion of radial and tangential lamellae

etc.

have distinctly different features. Our study reveals that the "nuclei" at domain II compose of locally ordered chains and the induced memory effect could not be erased under annealing treatment

while the "nuclei" at domain III compose of crystal fragments

which will aggregate under annealing process. Based on our results

highly schematic diagrams are proposed to illustrate the probable physical characteristics of the melt structures at the three different domains.