The effect of some thiosemicarbazide compounds on thermal oxidation of polypropylene

Abstract The effect of some 1–4 disubstituted thiosemicarbazide 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.