Recognition of the Syndiotactic Polypropylene Polymorphs via Dynamic-mechanical Analysis

摘要

Three Syndiotactic polypropylene samples were crystallized under different conditions in order to obtain different polymorphs. A first sample was crystallized at high temperature, obtaining the helical form Ⅰ; a second was crystallized from the melt at 0℃ for many days obtaining the trans-planar mesophase; a third sample was obtained by solvent induced crystallization followed by annaeling of the trans-planar mesophase, leading to a mixture of both the helical forms Ⅰ and Ⅱ. In the dynamic-mechanical analysis the helical form Ⅰ showed only one peak of tan 6 corresponding to the amorphous glass transition. The other polymorphs also showed this transition centered at about the same temperature. Beside the peak corresponding to the Tg, the trans-planar mesophase was characterized by a peak appearing at 70℃, and the helical form Ⅱ by a peak at 100℃. These peaks, unambiguously associated to transitions of the different forms, can be considered a distinctive evidence for the polymorphs obtained in different processing conditions.