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

摘要

The elusive helical form II of syndiotactic polypropylene (sPP), not yet fully clarified, was recognized in a fiber drawn at 90degreesC 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 100degreesC; 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.