Changes in the crystalline phase during the thermo-oxidation of a metallocene isotactic polypropylene. A DSC study

The changes in the crystalline phase characteristics of a metallocene isotactic polypropylene ( i-PP), during low temperature thermal degradation, have been analysed. This study shows the liability of the higher T m crystalline associations to be affected by the physicochemical changes produced in every stage of the thermo-oxidation. First, a small fraction corresponding to the highest T m crystal entities are involved in the physical reorganization process which takes place in the induction period, before any irreversible chemical change. Second, they are also selectively removed in the autoacceleration stage. This analysis shows not only that the crystalline phase of this i-PP is highly metastable, as it is obtained from the polymerization reaction, but also that the higher the T m of the associations the more liable they are to be affected by oxidation.