Compatible poly(vinyl chloride)/chlorinated polyurethane blends: thermal characteristics

The thermal behaviour of a series of solution-cast blends of poly(vinyl chl oride)/chlorinated 2,4-toluenediisocyanate-based polyurethane (PVC/CPU) pol ymers has been examined using differential scanning calorimetry, scanning e lectron microscopy and thermogravimetric analysis either alone or coupled w ith infrared spectroscopy. It has been found that the decomposition proceed s through a two-step route; the main, decisive degradation stage in the 200 -320 degrees C temperature range was found to be a result of parallel react ions of PVC and PU decomposition. This was also confirmed by Ozawa-Flynn-Wa ll kinetic analysis-the activation energy remained constant for degrees of conversion >0.3. The reasons for better thermal stability of some PVC/CPU b lends can be explained by analysis of specific interactions between the C=O groups of the urethane segments and the alpha-hydrogen of the chlorinated polymer or a dipole-dipole -C=O ... Cl-C- interaction. On the other hand, t he rate of diffusion of Volatile products through microphase domain structu re may differ due to changes in morphology arrangement thus considerably af fecting the overall decomposition route. (C) 1999 Elsevier Science Ltd. All rights reserved.