The effect of some thiosemicarbazide compounds on thermal oxidation of polypropylene

The effect of some 1-4 disubstituted thio semi carbazide compounds (TSC), including metal complexes, on thermal oxidation of isotactic polypropylene, has been studied, based on the knowledge that TSC contain various chemical groups such as C=S, -NH- that act as radical scavengers. All compounds exhibit antioxidant properties that represent around half of the effectiveness of Irganox 1076 (a strong phenolic antioxidant) during the induction period and around a quarter of this during the propagation period. The influence of X- atom (as a substituent in the 1st position) decreases in the following order: H > Cl > Br. R-group (as a substituent in 4th position) seems to exhibit lower influence than X (R = cyclohexyl, or phenyl ethyl). TSC complexes with Ni are more effective antioxidants as compared to TSC ligands. The activation energy of oxidation of isotactic polypropylene (i-PP) in the presence of Ni-complexes is very low as compared to the values found in the case of those free of additive i-PP or with other metal complexes. A compensation effect seems to be involved in these cases. A synergistic effect has been observed in the case of Ni(A2)(2)-Irganox 1076 couples, while with similar A5 and A6 couples, additive and antagonistic effects were observed, respectively. (C) 2004 Elsevier Ltd. All rights reserved.