Preparation, photochemical stability and photostabilising efficiency of adducts of pyrene and hindered amine stabilisers in iPP matrix

Abstract

The photostabilising efficiency of compounds containing pyrene as chromophore linked to hindered amine stabiliser (HAS) has been evaluated in photo-oxidation of isotactic polypropylene. Four series of compounds were prepared which have bridges formed either by methylene groups of different length or carbonyl group in α-position to pyrene ring. All derivatives of this type exhibited some efficiency. The most effective was 1-oxo-2,2,6,6-tetramethyl-4-piperidinyl-1-pyrenylacetate (IId) which exhibited an induction period about half the length at 2×10 −3 mol kg −1 compared with 2,2,6,6-tetramethyl-4-piperidinol or 1-oxo-2,2,6,6-tetramethyl-4-piperidinol under the similar conditions, monitored by IR spectroscopy. Emission spectroscopy revealed that the chromophore (pyrene) decomposes rapidly when it is used alone or when is linked to HAS in the form of parent amine or N-oxyl radicals. The decomposition rate is slower in the case of N-oxyl radicals. The increase of emission in the case of N-oxyl radicals at the beginning of irradiation indicates the reaction of this radical with other radicals formed during photo-oxidation. These reactions result in non-radical products and consequently in increase of emission due to switching off the intramolecular quenching.