Effect of stereoregularity on the thermo-oxidative degradation of polypropylenes

The effect of stereoregularity on the thermo-oxidative degradation of polyp ropylenes, isotactic (IPP) and syndiotactic (SPP), was examined by means of chemiluminescence (CL), infrared spectroscopy and molecular weight measure ment and their thermal stability was compared with that of high density pol yethylene (HDPE). SPP was extremely stable to the thermal oxidation and CL signals appeared much later than in IPP and even later than in HDPE. For ex ample, at 130 degrees C SPP showed no CL signals at all even after 7600 min , while IPP showed a maximum peak after 100 min and HDPE first peak after 4 60 min. At 140 degrees C, CL signals from SPP appeared at last after 2835 m in, and after 45 min from IPP and 240 min from HDPE. Changes in infrared (I R) spectra and molecular weights of the oxidized samples coincided with the results obtained from CL measurement. From the results obtained it was con cluded that the stereoregularity of polypropylenes definitely affects their thermal oxidation and SPP is much more stable than IPP. (C) 1999 Elsevier Science Ltd. All rights reserved.