Secondary and t e r t i a r y h i n d e r e d amines o f t h e p i p e r i d y l t y p e and many o t h e r p i p e r i d y l compounds can p r o t e c t v a r i o u s polymers a g a i n s t o x i d a t i o n s i n i t i a t e d by l i g h t , h e a t and i o n i z i n g r a d i a t i o n .
These amines s t a b il i z e by b e i n g c o n v e r t e d t o a s e r i e s o f p r o d u c t s which can scavenge w i t h h i g h s t o i c h i o m t r y t h e main r a d i c a l s respons i b l e f o r t h e o x i d a t i v e chain.
T h i s h i g h s t o i c h i o m e t r y r e s u l t s from t h e c y c l i c a l r e g e n e r a t i o n o f t h e scavenging p i p e r i d y l species.
The e f f i c i e n c y 3 f t h e h i n d e r e d amines as a n t i o x i d a n t s i n p o l y o l e f i n s i s enhanced by t h e i r a b i l i t y t o a s s o c i a t e w i t h t h e u n s t a t l e o x i d i z e d domains i n which photo-and thermal o x i d a t i o n s r i l l e v e n t u a l l y r e i n it i a t e .
Secondary amines can a l s o s l o w l y decompose i n t r am o l e c u l a r l y hydrogen bonded h y d r o p c r o x i d e groups o f t h e t y p e found i n p o l y p r o p y l e n e . T h i s process may d e s t r o y t h e u n s t a b l e o x i d a t i o n p r o d u c t b e f o r e t h e hydroperoxide can r e -i n i t i a t e o x i d a t i o n and a l s o generates a n o t h e r p o w e r f u l a n t i o x i d a n t , a hydroxylamine. D e s J i t e t h e c y c l i c a l r eg e n e r a t i o n o f a c t i v e p i p e r i d y l r a d i c a l scavengers, s i d e r e a c t i o n s can produce non-scavenging p r o d u c t s or even p h o t o -i n i t i a t o r s which w i l l p r o g r e s s i v e l y accumulate and s t r a n g l e t h e a n t i o x i d a n t a c t i v i t i e s . E O ='F6oo%. d) 2 x lo-* mol. kQ-1, 2.2.6.6tetramethyl -4 -D i ~e r i d y l -N -o x y l . . . . . e ) 2 x 10-2 mol. k i -1 , octadecyl 6 -( 3 . 5 -d i -e -b u t y l -4 -h y d r i x y p h e n y l )propionate.