A Decade of Hindered Amine Light Stabilizers - ACS Symposium

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A Decade of Hindered Amine Light Stabilizers H E L M U T K. M Ü L L E R Plastics and Additives Division, CIBA-GEIGY, Ltd., Basel, Switzerland

Shortly after the first synthesis of triacetoneamineN-oxyl, tetramethyl-hindered piperidines were found to be effective light stabilizers for polymers. That finding unleashed an extensive worldwide investigation of those compounds which to date has resulted in the filing of more than 600 patent applications. Hindered amine light stabilizers have proven effective for the weathering stabilization of a large number of major polymers, especially polypropylene, polyethylene, polystyrene, impact polystyrene, ABS, SAN, polyurethane as well as thermoplastic and thermosetting coatings. New applications for hindered amine stabilizers are found regularly. They are clearly the most significant development of polymer stabilization of the decade. During the last 15 years, hindered amine light stabilizers, now commonly referred to as HALS (_1), have been one of the most actively investigated classes of polymer additives. This statement is easily substantiated by the fact that since the late Sixties, more than 600 patent applications involving HALS have been filed by more than 80 chemical companies or research institutes. The list of companies involved reads like a "Who's Who" of major chemical producers. As can be seen in Figure 1, after an induction period of about five years, patents have been filed at a steady rate of approximately 50 applications per year. By far, the biggest number of patented HALS is based on derivatives of triacetoneamine, a condensation product of acetone and ammonia (Figure 2). Some examples of structural variants not based on triacetoneamines are shown in Figure 3. As far as we know today, all but one of the commercially available hindered amine stabilizers are derived from triacetoneamine. The number of scientific and technical papers, many of them dealing with the mechanisms of action of HALS, also runs into the hundreds. What started all this effort was the observation by a Dr. K. Murayama (2^) that triacetoneamine-N-oxyl, an unusually 0097-6156/85/0280-0055$06.00/0 © 1985 American Chemical Society In Polymer Stabilization and Degradation; Klemchuk, P.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

A N D

DEGRADATION

Downloaded by GEORGETOWN UNIV on September 4, 2014 | http://pubs.acs.org Publication Date: June 14, 1985 | doi: 10.1021/bk-1985-0280.ch004

P O L Y M E R STABILIZATION

F i g u r e 3 . S t r u c t u r a l v a r i a n t s of h i n d e r e d amine l i g h t stabilizers.

In Polymer Stabilization and Degradation; Klemchuk, P.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.


4.

M U L L E R

Hindered Amine Light Stabilizers

57

s t a b l e f r e e r a d i c a l , s y n t h e s i z e d f o r the f i r s t time by M. B . Neiman and coworkers (_3), was found t o be a h i g h l y e f f i c i e n t l i g h t s t a b i l i z e r f o r a v a r i e t y of polymers. However, t r i a c e t o n e a m i n e N - o x y l d i d not l e n d i t s e l f t o p r a c t i c a l use on account o f i t s p h y s i c a l and c h e m i c a l p r o p e r t i e s . The compound e a s i l y undergoes thermally-induced disproportionation (4). It i s v o l a t i l e and c o l ored and t h e r e f o r e i m p a r t s c o l o r t o the s u b s t r a t e t o be s t a b i l i z e d . A n o t h e r drawback t o t h e t r i a c e t o n e a m i n e - N - o x y l i s i t s p o s s i b l e chemical r e a c t i o n s with phenolic a n t i o x i d a n t s . Through e l i m i n a t i o n o f the k e t o group i n t h e 4 - p o s i t i o n , o b v i o u s l y r e s p o n s i b l e f o r the t h e r m a l i n s t a b i l i t y ( 5 ) , and by s w i t c h i n g from the N - o x y l compounds to t h e p a r e n t amines as " s t a b l e r a d i c a l p r e c u r s o r s , " which indeed proved t o be h i g h l y e f f e c t i v e l i g h t s t a b i l i z e r s ( 6^, the drawbacks o f t r i a c e t o n e a m i n e - N - o x y l have been overcome ( F i g u r e 4 ) . A f t e r t h e p u b l i c a t i o n o f the f i r s t HALS p a t e n t s , s y n t h e s i s and a p p l i c a t i o n a l work were s t a r t e d t o check the m e r i t s o f t h i s new and unusual l i g h t s t a b i l i z e r s t r u c t u r e . The f i n d i n g s o f the Japanese workers were c o n f i r m e d i n f u l l . E s p e c i a l l y i n p o l y p r o p y l e n e , the performance o f HALS was almost u n b e l i e v a b l y h i g h i n comparison t o the s t a t e - o f - t h e - a r t ; i . e . , UV a b s o r b e r s , N i complexes and b e n z o ates. E a r l y f i n d i n g s o f HALS e f f e c t i v e n e s s l e d t o a c o o p e r a t i v e e f f o r t between the Sankyo company o f Japan and CIBA-GEIGY o f S w i t z e r l a n d b e i n g i n i t i a t e d w i t h the o b j e c t i v e o f c o m m e r c i a l i z i n g t h i s important c l a s s of l i g h t s t a b i l i z e r s . D e s p i t e the combined e f f o r t s , t e s t i n g , s e l e c t i o n and p r o c e s s development o f s u i t a b l e HALS c a n d i d a t e s took t i m e , because o f the u n u s u a l l y l o n g t e s t i n g times r e q u i r e d and the r a p i d l y growing number o f compounds a v a i l able. F i n a l l y i n 1973, t h r e e d e v e l o p m e n t a l HALS compounds were sampled on a worldwide b a s i s as l i g h t s t a b i l i z e r s w i t h emphasis on p o l y o l e f i n s and s t y r e n i c polymers ( F i g u r e 5 ) . One o f the t h r e e , bis(2,2,6,6-tetramethylpiperidinyl-4) s e b a c a t e (HALS I ) , s u r v i v e d the s a m p l i n g s t a g e and was c o m m e r c i a l i z e d by the second h a l f o f 1974 (7). Early

Results

The f i r s t papers on the performance o f h i n d e r e d amine l i g h t s t a b i l i z e r s were p u b l i s h e d by F . Gugumus (8^) and K. Leu (9) i n 1974. One o f t h e r e a s o n s why n e a r l y h a l f a decade l a p s e d between the b a s i c i n v e n t i o n and the f i r s t c o m m e r c i a l i z e d HALS p r o d u c t i s i n d i c a t e d by the d a t a i n F i g u r e 6 as p u b l i s h e d by F . Gugumus. The d e l a y i n c o m m e r c i a l i z i n g HALS was i n p a r t due t o the worldwide r e c e s s i o n i n 1975 caused by the f i r s t o i l c r i s i s and a l s o because more time was needed t o g a i n a broad a c c e p t a n c e i n the m a r k e t p l a c e due t o the f a c t t h a t HALS-based systems impart t h r e e t o f o u r times h i g h e r s t a b i l i t y t o a number o f p l a s t i c m a t e r i a l s than had been a c h i e v a b l e with l i g h t s t a b i l i z e r s p r e v i o u s l y a v a i l a b l e (9). O r i g i n a l l y , our outdoor exposure s t u d i e s were run i n c e n t r a l I t a l y ; l a t e r we s w i t c h e d t o e x p o s i n g samples i n F l o r i d a i n o r d e r t o d e c r e a s e the time o f e x p o s u r e . However, even i n F l o r i d a , depending on the s t a b i l i z e r c o n c e n t r a t i o n s , samples c o n t a i n i n g HALS may take y e a r s t o fail. F o r example, a w h i t e pigmented p o l y p r o p y l e n e s t r e t c h e d tape w i t h 0.6% b i s ( 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n y l - 4 ) s e b a c a t e has not f a i l e d yet a f t e r more t h a n s i x y e a r s outdoor w e a t h e r i n g i n F l o r i d a 1



POLYMER STABILIZATION AND DEGRADATION

USP

Figure 4 .

3 536 722

USP

3 542

729

The d i s c o v e r y of HALS ( t r a n s i t i o n from N - o x y l s ) . HALS-I

F i g u r e 5.

F i g u r e 6.

Developmental HALS sampled i n 1973.

Outdoor w e a t h e r i n g of PP s t r e t c h e d tape

(Italy).



4.

MULLER


59

(Figure 7). The o u t s t a n d i n g e f f e c t i v e n e s s o f b i s ( 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n y l - 4 ) s e b a c a t e (HALS I) i n s t a b i l i z i n g 2 mm p o l y p r o p y l e n e p l a q u e s on outdoor w e a t h e r i n g i n A r i z o n a can c l e a r l y be seen from t h e d a t a shown i n F i g u r e 8. For many y e a r s , p o l y p r o p y l e n e f i b e r has been the s u b j e c t o f i n - d e p t h r e s e a r c h aimed at i m p r o v i n g i t s l i g h t s t a b i l i t y . The i n h e r e n t l i g h t s e n s i t i v i t y o f p o l y p r o p y l e n e and the h i g h s u r f a c e t o - v o l u m e r a t i o o f f i b e r s are the prime reasons f o r the d i f f i c u l t i e s i n s t a b i l i z i n g polypropylene f i b e r . The c o n s i d e r a b l e i m p r o v e ment a c h i e v e d w i t h b i s ( 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n y l - 4 ) sebacate was, however, d r a s t i c a l l y reduced when p o l y p r o p y l e n e f i n e f i b e r s (up to 15 dpf) or a r t i c l e s made t h e r e o f , were t r e a t e d at e l e v a t e d temperatures i n t e x t i l e f i n i s h i n g o p e r a t i o n s i n v o l v i n g l a t e x backi n g and t e n t e r i n g . It was soon r e c o g n i z e d t h a t the performance l o s s a f t e r thermotreatment was due t o the p h y s i c a l d e p l e t i o n o f the s t a b i l i z e r as a consequence o f i t s s m a l l s i z e , r e l a t i v e l y r a p i d r a t e o f m i g r a t i o n , and i t s r e l a t i v e l y low m o l e c u l a r w e i g h t . T h i s e x p e r i e n c e i n i t i a t e d t h e development o f h i g h e r m o l e c u l a r weight compounds (10) and e v e n t u a l l y o f p o l y m e r i c l i g h t s t a b i l i z e r s (11) . One answer t o the performance l o s s on thermotreatment o r t e n t e r i n g o f p o l y p r o p y l e n e f i b e r was a s t a b i l i z e r w i t h a m o l e c u l a r c o m b i n a t i o n o f a s t e r i c a l l y h i n d e r e d phenol and a s t e r i c a l l y h i n d e r e d amine. The s t r u c t u r e o f b i s ( 1 , 2 , 2 , 6 , 6 - p e n t a m e t h y l - 4 piperidinyl) l-butyl-l-(3,5-di-tert-butyl-4-hydroxybenzyl)malonate, which e x e m p l i f i e s t h i s c o m b i n a t i o n , i s shown i n F i g u r e 9. The i d e a behind such a p r o d u c t was t o combine the n e c e s s a r y i n c r e a s e i n m o l e c u l a r weight w i t h an a d d i t i o n a l s t a b i l i z i n g f u n c t i o n . The p h e n o l i c m o i e t y imparts t h e r m a l s t a b i l i t y ; the a m i n i c p a r t p r o v i d e s the l i g h t s t a b i l i t y as shown i n T a b l e 1. The l i g h t exposure d a t a i n T a b l e 1 were g e n e r a t e d w i t h a X e n o t e s t 1200 l i g h t exposure device. P o l y m e r i c HALS. The f i n a l answer t o the p o l y p r o p y l e n e f i b e r s t a b i l i t y problem was the development o f p o l y m e r i c HALS. The s t r u c t u r e s o f two such p o l y m e r i c compounds, p o l y m e r i c HALS-A and p o l y m e r i c HALS-B a r e shown i n F i g u r e 10. P o l y m e r i c HALS have t o be c o n s i d e r e d the s t a b i l i z e r s o f c h o i c e f o r s t a b i l i z i n g p o l y p r o p y l e n e fiber. They o f f e r e x c e l l e n t performance as l i g h t and heat s t a b i l i z e r s at moderate use c o n c e n t r a t i o n s ( 1 2 ) ; some r e p r e s e n t a t i v e d a t a are p r e s e n t e d i n T a b l e 2. M o r e o v e r , t h e y s o l v e the p o l y p r o p y l e n e f i n e f i b e r problem r e l a t e d to t e n t e r i n g i n the use o f l a t e x b a c k ing. P o l y p r o p y l e n e f i n e f i b e r s s t a b i l i z e d w i t h the a f o r e - m e n t i o n e d compounds a r e v i r t u a l l y u n a f f e c t e d by thermotreatment as shown i n T a b l e 3. The a c r y l i c l a t e x t r e a t m e n t , t h e most s e v e r e exposure c o n d i t i o n , s h o u l d s i m u l a t e the e x p e r i e n c e o f p o l y p r o p y l e n e f a b r i c s i n u p h o l s t e r y and c a r p e t i n g a p p l i c a t i o n s where l a t e x a p p l i c a t i o n and thermotreatment t o e l i m i n a t e f a b r i c s t r e s s e s a r e r e a l e x p e r i ences. The d a t a i n T a b l e 3 show c l e a r l y t h a t the e x c e l l e n t l i g h t s t a b i l i t y c o n f e r r e d by the low m o l e c u l a r weight H A L S - I , bis(2,2,6,6-tetramethylpiperidinyl-4) s e b a c a t e d i s a p p e a r s almost e n t i r e l y a f t e r l a t e x treatment and t e n t e r i n g . It s h o u l d be mentioned t h a t p o l y m e r i c HALS-A, the p o l y e s t e r t y p e , i s b r o a d l y approved f o r p o l y o l e f i n a r t i c l e s i n c o n t a c t w i t h f o o d .



60

P O L Y M E R STABILIZATION

A N D DEGRADATION

YEARS

.3 Z

> 1 3 0 0 KLY

HALS-I

> 7 YEARS .3Z

.1 Z HALS-I

-HALS-I

:

65 Z RET.

95% RET.

IMPACT

IMPACT

.1 Z HALS-I

.3 Z BEN-

.3 Z -1

ZOTR.

BENZOTR.

DONTROL CONTROL UNPIGMENTED

.5 Z T i 0 2 *

RUTILE

F i g u r e 8. L i g h t s t a b i l i t y o f 2 mm p o l y p r o p y l e n e plaques KLY t o 50% r e t e n t i o n o f impact s t r e n g t h .

(Arizona);



4.

MULLER


61

F i g u r e 9. M o l e c u l a r c o m b i n a t i o n of a s t e r i c a l l y h i n d e r e d phenol and HALS (HALS-PH).

Table 1. Performance of a M o l e c u l a r Hindered Phenol-HALS Combination i n PP F i b e r 120/12 DEN (Exposure: X e n o t e s t 1200) OVEN AGING AT 1 1 0 ° C

LIGHT S T A B I L I T Y

DAYS TO FAILURE

XO 1 2 0 0 HOURS TO FAILURE

12

500

0,1% HALS-PH

15

1200

0,2% HALS-PH

24

2000

0,4% HALS-PH

26

3000

0,2% COMMERCIAL

AO

H

/
250

T a b l e 7. I n f l u e n c e o f China C l a y on L i g h t S t a b i l i t y of LDPE Film: F l o r i d a E x p o s u r e ; KLY t o 50% R e t e n t i o n o f E l o n g a t i o n WITH 3 % CHINA CLAY

ADDITIVES

WITHOUT

.15% Ni-COMPOUND

210 KLY

85 KLY

255

90

>400

220

.15% BENZOPH.-UVA .15% HALS-A .15% BENZOPH.-UVA .15% HALS-B .15% BENZOPH.-UVA


POLYMER STABILIZATION AND DEGRADATION

68

Literature Cited 1. 2. 3. 4. 5. 6. 7.


8. 9. 10. 11. 12. 13. 14. 15.

Mod. Plast. Intern. 13, October, 51 (1983). K. Murayama, Pharmacia (Japan) 10, 573 (1974). M. B. Neiman, E. G. Rozantsev and Y. G. Mamadova, Nature, 196, 472 (1962). K. Murayama and T. Yoshioka, Bull. Chem. Soc. Japan, 42, 2307 (1969). K. Murayama et a l . , USP 3,536,722 (1970) Sankyo Co. Ltd. K. Murayama et a l . , USP 5,542,729 (1970) Sankyo Co. Ltd. Preliminary Product Information: TINUVIN 770, Ciba-Geigy Ltd., 1975. F. Gugumus, Fourth European Plastics and Rubber Conference, 1974, Paris. K. Leu, The Plastics Institute of Australia, Residential Technical Seminar, 1974, Teorigal, Australia. Preliminary Product Information: TINUVIN 144, Ciba-Geigy Ltd., 1978. Preliminary Product Information: TINUVIN 622, Ciba-Geigy Ltd., 1978; CHIMASSORB 944, Ciba-Geigy Ltd., 1979. F. Gugumus, Third International Conference, Polypropylene Fibers and Textiles, 1973, York, Great Britain. W. Rembold and G. Berner, Fifth International Conference on Advances in the Stabilization and Controlled Degradation of Polymers, 1983, Zurich, Switzerland. B. Gilg, Fifth European Plastics and Rubber Conference, 1978, Paris. Technical Information on Image Dye Stabilizer G 15-994, Ciba-Geigy Ltd., 1982.

RECEIVED February 11, 1985


A Decade of Hindered Amine Light Stabilizers - ACS Symposium

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