Further Understanding on the Three Domains of Isotactic Polypropylene by Investigating the Crystalline Morphologies Evolution after Treatment at Different Domains

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 i PP 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.