A possible explanation to the structure change of isotactic polypropylene occurring at about 135 degrees C

The in situ Fourier transform infrared spectroscopic study of isotactic pol ypropylene (iPP) shows that a structure change occurs at about 135 degreesC . Some experimental results suggest that this structure change may result f rom the disordering of helical sequences in the noncrystalline region, whic h can be further confirmed by the in situ infrared observation of chloride polypropylene (Cl-PP). If the iPP sample is drawn, the transition temperatu re is elevated. According to the change of infrared absorbance with tempera ture between 135 and 155 degreesC, the various regularity bands of iPP can be rearranged in terms of the order degree from high to low: 940, 1220, 116 7, 1303, 1330, 841, 998, 900, 808, 1100 and 973 cm(-1). This sequence is id entical with our recent observation based on the melting of iPP crystals. ( C) 2001 Elsevier Science Ltd. All rights reserved.