On-Line FT-IR Spectroscopic Study of the Disorientation of Uniaxially Stretched Isotactic Poly(Propylene) upon Heating

The study of molecular orientation in polymers is of great interest because of its importance in the structural features and mechanical properties of polymer materials. During the past decades, the orientation behavior of isotactic poly(propylene) (iPP) has been well investigated by many experimental methods, such as wide-angle Xray diffraction, polarized  uorescence, birefringence, sonic modulus, broad-line NMR, ultraviolet, infrared dichroism, and polarization Raman spectroscopy.1–12 Generally, it is found that with increasing draw ratio the orientation of the crystalline phase increases rapidly and approaches perfect orientation at a relatively low draw ratio, while the orientation of the noncrystalline phase increases much more slowly. Thus, at a low draw ratio, the orientation function of the crystalline phase is higher than that of the noncrystalline phase. However, many oriented materials are used at an elevated temperature. On heating the oriented sample, the reverse process of orientation, the disorientation, will occur. But only little attention has been paid to the relationship between disorientation and temperature hitherto. Now, based on polarization infrared spectroscopy, we develop a simple and rapid technique for on-line measurement of orientation change of macromolecular chains in uniaxially stretched iPP upon heating.