Thermally induced structural and dynamic-mechanical transition of form II of syndiotactic polypropylene

The elusive helical form II of syndiotactic polypropylene (sPP), not yet fully clarified, was recognized in a fiber drawn at 90°C and its thermally induced transitions were followed by x‐ray diffraction and dynamic‐mechanical analysis as a function of temperature. It was found that this form is stable up to 100°C; afterwards a melting and recrystallization phenomenon occurs leading to the ordered form I. In correspondence to this structural change, the dynamic‐mechanical analysis shows a strong dissipation peak that can be unambiguously associated to the transition and, therefore, can be considered distinctive evidence of the presence of form II.