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

The thermal behaviour of a series of solution-cast blends of poly(vinyl chloride)/chlorinated 2,4-toluenediisocyanate-based polyurethane (PVC/CPU) polymers has been examined using differential scanning calorimetry, scanning electron microscopy and thermogravimetric analysis either alone or coupled with infrared spectroscopy. It has been found that the decomposition proceeds through a two-step route; the main, decisive degradation stage in the 200–320°C temperature range was found to be a result of parallel reactions of PVC and PU decomposition. This was also confirmed by Ozawa-Flynn-Wall kinetic analysis—the activation energy remained constant for degrees of conversion >0.3. The reasons for better thermal stability of some PVC/CPU blends can be explained by analysis of specific interactions between the CO groups of the urethane segments and the α-hydrogen of the chlorinated polymer or a dipole-dipole CO· · ·ClC interaction. On the other hand, the rate of diffusion of volatile products through microphase domain structure may differ due to changes in morphology arrangement thus considerably affecting the overall decomposition route.