AbstractThe behavior of organic phosphites as antioxidants for polyethylene, costabilizer, and metal‐deactivator for poly(vinyl chloride) (PVC), has been studied by Thermox‐meter and Brabander plastograph. It was found, that their antioxidative effectivity is determined by the self‐stability of the investigated phosphites, namely the volatility, the hydrolysis and oxidation sensitivity. At the same time, the stabilizing and metal‐deactivating effect for PVC with this technique did not show significant diff