Spectral and photostabilizing characteristics of adducts of aromatic hydrocarbons and hindered amine stabilizers

Abstract

The spectral characteristics and photostabilizing efficiency of adducts of aromatic hydrocarbons and hindered amine stabilizers (HASs) were investigated in isotactic polypropylene. The aromatic hydrocarbons were naphthalene and pyrene. The HAS has the 2,2,6,6-tetramethylpiperidine structural unit. There was a direct link between these structural units or methylene groups separated them. Absorption and emission spectra of adducts in cyclohexane and isotactic polypropylene were nearly the same. Generally, a higher quantum yield of fluorescence was observed in the polymer matrix due to restriction of the rotation of the bulky substituent which is the path for radiationless deactivation. No acceleration of isotactic polypropylene photooxidation with naphthalene or its derivatives without the HAS structural unit was observed. Adducts of naphthalene-HAS exhibited lower photostabilization efficiency than HAS without linked naphthalene. Adducts of pyrene and HAS do not exhibit any stabilization efficiency in photooxidation of isotactic polypropylene. The N-oxyl of the parent adduct exhibits some efficiency in the later stage of photooxidation. The antagonistic effect between aromatic hydrocarbons and HASs linked together was demonstrated.