NOR and nitroxide-based HAS in accelerated photooxidation of carbon-chain polymers; Comparison with secondary HAS: An ESRI and ATR FTIR study

Abstract

Understanding processes resulting in heterogeneous degradation in polymers is of extreme importance for improving their stabilization and minimizing negative impact of photooxidation on the material properties. We adopted modern physical techniques for studies of spatial distribution of intermediates and products of photodegradation during accelerated ageing of four commodity polymers, polypropylene (PP), polyethylene (PE), polystyrene (PS) and poly(ethylene-co-norbornene) (Topas ®, TP) stabilized with hindered amine stabilizer (HAS). Concentration profiles of nitroxides inside polymer plaques along the direction perpendicular to their surface were determined by electron spin resonance imaging (ESRI) as a function of the duration of the accelerated photooxidation. We present data characterizing stabilization activity of three alkoxyamine derivatives of HAS (Tinuvin ® NOR 123, Tinuvin ® NOR 371, Flamestab ® NOR 116), Chimasorb ® 119 structurally similar to Flamestab ® NOR 116, and nitroxide-based HAS Dastib ® 1045 and compare them with the data characterizing stabilization activity of the secondary HAS (>NH) Tinuvin ® 770. ESRI data are complemented by ATR FTIR spectroscopic detection of oxidation products on the surface and inside the plaques and by data characterizing diffusive optical transmittance of the polymer plaques in the spectral region 280–400 nm (terrestrial range of the solar UV radiation).