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

The photostabilising efficiency of compounds containing pyrene as chromopho re linked to hindered amine stabiliser (HAS) has been evaluated in photo-ox idation of isotactic polypropylene. Four series of compounds were prepared which have bridges formed either by methylene groups of different length or carbonyl group in a-position to pyrene ring. All derivatives of this type exhibited some efficiency. The most effective was 1 -oxo-2,2,6,6-tetramethy l-4-piperidinyl-1-pyrenylacetate (IId) which exhibited an induction period about half the length at 2 x 10(-3) mol kg(-1) compared with 2,2,6,6-tetram ethyl-4-piperidinol or 1-oxo-2,2,6,6-tetramethyl-4-piperidinol under the si milar conditions, monitored by IR spectroscopy. Emission spectroscopy revea led 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. Th e 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 p hoto-oxidation. These reactions result in nonradical products and consequen tly in increase of emission due to switching off the intramolecular quenchi ng. (C) 2000 Elsevier Science Ltd. All rights reserved.