Hexahydropyrimidines as Hindered Amine Light Stabilizers - ACS

12 Downloaded by UNIV OF SYDNEY on August 15, 2013 | http://pubs.acs.org Publication Date: June 14, 1985 | doi: 10.1021/bk-1985-0280.ch012

Hexahydropyrimidines as Hindered Amine Light Stabilizers C. E. R A M E Y and C. J . ROSTEK Chemical Division, Ferro Corporation, Bedford, O H 44146

Novel hindered amine light stabilizers (HALS) derived from 2,2,4,4,6-pentamethylhexahydropyrimidine were shown to exhibit excellent performance in exposed polypropylene films. Test data for other HALS compounds prepared from the previously described 2,2,5,5-tetramethyl-4-imidazolidinone and 4,4-dimethyloxazolidine ring systems are provided for comparison. Inferior performance was generally observed for those additives which would be expected to form low molecular weight nitroxide radicals upon oxidation. A relatively large extention of film lifetime was produced by formulations containing a combination of HALS and commercial hydroxybenzoate stabilizer. This effect was not evident when HALS compounds containing an intramolecualr hydroxybenzoate group were tested. Hindered amine light stabilizers are at least partially converted to their corresponding nitroxides during the processing (1) and exposure of stabilized polymers. Allen (2) showed that the hydroperoxides present in thermally oxidized polypropylene were capable of effecting this transformation under compression molding conditions. Hindered amine nitroxides have been recognized as key intermediates in the stabilization mechanism of HALS compounds Q , 3_-5). Although the parent hindered amines may contribute to photostabilization (6^), in our development work the stability and nature of the nitroxide radicals resulting from HALS oxidation were assumed to be critical to viable stabilizer activity. At the outset of our HALS program a number of chemically stable nitroxide free radicals had been identified from work in spin labelling (7^), but only derivatives of tetramethylpiperidine had appeared in the additive marketplace.

0097-6156/85/0280-0149$06.00/0 §> 1985 American Chemical Society In Polymer Stabilization and Degradation; Klemchuk, P.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

150

POLYMER STABILIZATION AND DEGRADATION

Downloaded by UNIV OF SYDNEY on August 15, 2013 | http://pubs.acs.org Publication Date: June 14, 1985 | doi: 10.1021/bk-1985-0280.ch012

We wanted to i n v e s t i g a t e how the e f f e c t i v e n e s s of a g i v e n l i g h t s t a b i l i z e r might depend upon the p a r t i c u l a r h e t e r o c y c l i c amine used in i t s synthesis. The p o l a r i t y , v o l a t i l i t y and c o m p a t i b i l i t y of the o r i g i n a l a d d i t i v e were a l s o known to be i m p o r t a n t f a c t o r s i n d e t e r m i n i n g s t a b i l i z e r performance ( 8 ) . Three h e t e r o c y c l i c r i n g systems were chosen p r i m a r i l y f o r t h e i r ease of s y n t h e s i s . The compounds 2,2,4,4,6-pentamethylhexahydropyrimidine (HHP) ( 9 , 1 0 ) and 2 , 2 , 5 , 5 , t e t r a m e t h y l - 4 - i m i d a z o l i d i n o n e (IMZ) ( 1 1 - 1 3 ) were chosen as s t a r t i n g m a t e r i a l s to e v a l u a t e the e f f e c t of d e r i v a t i v i z a t i o n and s u b s t i t u t i o n on the a c t i v i t y of the r e s u l t i n g l i g h t s t a b i l i z e r s . A few 4 , 4 , - d i m e t h y l o x a z o l i d i n e s were made from 2 - a m i n o - 2 - m e t h y l - l - p r o p a n o l and ketones to examine t h i s s t r u c t u r a l l y l i m i t e d r i n g system (see R e s u l t s and D i s c u s s i o n ) .

0

HHP

IMZ

4,4-Dimethyloxazolidine

Experimental The a d d i t i v e s were t e s t e d i n p o l y p r o p y l e n e ( P r o f a x 6501, Hercules) f i l m s c o n t a i n i n g 0.1% G o o d r i t e 3114 ( p h e n o l i c a n t i o x i d a n t of B . F . G o o d r i c h C o . ) and .05% c a l c i u m s t e a r a t e . The c a n d i d a t e a d d i t i v e s were added at 0.25% or 0.5% f i n a l c o n c e n t r a t i o n s as methylene c h l o r i d e s o l u t i o n s (100 ml methylene c h l o r i d e / l O O g p o l y p r o p y l e n e ) and the m i x t u r e s t i r r e d 15-20 m i n s . w h i l e the s o l v e n t was a l l o w e d to e v a p o r a t e . The r e s u l t a n t powder was then d r i e d and e x t r u d e d i n t o 3/32 i n c h s t r a n d , which was cut i n t o p e l l e t s . A f t e r d r y i n g , the p e l l e t s were e x t r u d e d i n t o a broad ( 8 " ) band. A 1/4" s e c t i o n was s l i t from the band and o r i e n t e d by drawing at 175°F at a 7:1 draw r a t i o . The d i m e n s i o n s o f the o r i e n t e d f i l m are about 1 x 80 m i l s . The o r i e n t e d f i l m specimens were mounted on aluminum frames and exposed on an A t l a s Weather-Ometer, Model 65WR. An 18 minute s p r a y c y c l e t o g e t h e r w i t h an 102 minute c y c l e at 55% r e l a t i v e h u m i d i t y and a p p r o x i m a t e l y 65°C was u s e d . At r e g u l a r i n t e r v a l s , the t e s t specimens were removed from exposure and t h e i r t e n s i l e s t r e n g t h measured on an I n s t r o n Model 1102. A d e c r e a s e i n t e n s i l e s t r e n g t h , e x p r e s s e d as t e n a c i t y , over the t e n s i l e s t r e n g t h of the same f o r m u l a t i o n before e x p o s u r e , i s a measure of the d e t e r i o r a t i o n of the p h y s i c a l p r o p e r t i e s of the p o l y m e r . " F a i l u r e " i n t h i s t e s t i s d e f i n e d as a l o s s of 50% or more of the i n i t i a l sample t e n a c i t y . P h o t o m i c r o g r a p h s to observe a d d i t i v e c o m p a t i b i l i t y i n the o r i e n t ed f i l m were t a k e n at 400X u s i n g a t r a n s m i s s i o n l i g h t m i c r o s c o p e . Blooming was measured at 70°C u s i n g u n o r i e n t e d f i l m samples 7 m i l i n thickness. Thermal o x i d a t i v e s t a b i l i t y was measured i n a c i r c u l a t i n g a i r oven at 140°C on p o l y p r o p y l e n e f i l m s 5" x 1" x . 0 2 5 " .

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

12. RAMEY AND ROSTEK


Results

Hexahydropyrimidines

151

& Discussion

The compounds i n T a b l e I r e p r e s e n t some e a r l y t r i a l s a r i s i n g from s c r e e n i n g IMZ d e r i v a t i v e s and o x a z o l i d i n e s . The lower a c t i v i t y shown by compounds (1) and (2) i s c o n s i s t e n t w i t h t h e o x a z o l i d i n e group b e i n g l o s t as a low m o l e c u l a r weight fragment a f t e r n i t r o x i d e f o r m a t i o n o c c u r s . T h i s i l l u s t r a t e s a drawback o f t h e o x a z o l i d i n e compounds compared t o o t h e r s y s t e m s , t h a t o n l y t h e amine n i t r o g e n and h i n d e r i n g group ( d e r i v e d from t h e s t a r t i n g k e t o n e ) a r e a v a i l a b l e t o b u i l d t h e m o l e c u l a r weight o f t h e s t a b i l i z e r . A s i m i l a r effect i s apparently shown by compound (5) w h i c h i s b r i d g e d t h r o u g h t h e h i n d e r e d amine n i t r o g e n s , a l l o w i n g t h e i m i d a z o l i d i n o n e group form low m o l e c u l a r weight n i t r o x i d e r a d i c a l s . Compound (3) i s a low m o l e c u l a r weight IMZ d e r i v a t i v e which showed a l o n g f i l m l i f e t i m e a t 0.5% c o n c e n t r a t i o n . However, t h i s a c t i v i t y was n o t r e f l e c t e d i n t h e h i g h e r m o l e c u l a r weight a n a l o g (4) which was t e s t e d a t a lower c o n c e n t r a t i o n . Here the methyleneamino group i s p r o b a b l y b e i n g l o s t from t h e 3 - p o s i t i o n o f t h e IMZ group due t o t h e r m a l i n s t a b i l i t y . T h i s i s c o n f i r m e d by the h i g h t h e r m o g r a v i m e t r i c a n a l y s i s (TGA) weight l o s s o f t h e e t h y l e n e d i amine d e r i v e d model compound ( 1 6 ) . I n T a b l e I I a r e shown some i n t e r m e d i a t e c a n d i d a t e s where b e t t e r a c t i v i t y i s b e g i n n i n g t o become a p p a r e n t . The s u b s t i t u t i o n of t h e hydroxybenzoate group i n compound (8) does not seem t o make much i m provement i n t h e a c t i v i t y o f t h e l o n g s i d e - c h a i n IMZ d e r i v a t i v e s . The polymer l i f e t i m e of t h e HHP based a d d i t i v e (9) was e n c o u r a g i n g , as the e a r l i e r f a i l u r e of d i i s o c y a n a t e adduct (10) was a t t r i b u t e d t o i t s lower c o m p a t i b i l i t y i n t h e p o l y p r o p y l e n e f i l m . In T a b l e I I I , t h e p o s i t i v e i n t e r a c t i o n between IMZ s t e a r a t e (6) and t h e hydroxybenzoate s t a b i l i z e r UV-Chek AM-340 i s shown. This degree of l i f e t i m e enhancement was not a c h i e v e d i n any of t h e HALS compounds s y n t h e s i z e d i n which t h e hydroxybenzoate group was p r e s e n t as an i n t r a m o l e c u l a r s u b s t i t u e n t . The p r o x i m i t y o f t h e h i n d e r e d p h e n o l i c group may i n some way a f f e c t g e n e r a t i o n o f t h e n i t r o x i d e r a d i c a l s from t h e amine n i t r o g e n .

The s u b s t i t u t i o n o f a hydroxybenzoate group f o r a s t e a r a t e group seemed t o have a d e t r i m e n t a l r e s u l t i n comparing compounds (14) and (15) i n T a b l e I V . I n c o r p o r a t i o n o f a more c o n v e n t i o n a l p h e n o l i c a n t i o x i d a n t group i n (13) may have s u p p r e s s e d a c t i v i t y even more. However, t h e e f f e c t o f p h y s i c a l f a c t o r s on t h e s t a b i l i z i n g a c t i v i t y of t h e s e a d d i t i v e s s h o u l d n o t be u n d e r e s t i m a t e d . The IMZ h y d r o x y benzoate compound (12) has good a c t i v i t y p o s s i b l y due t o i t s p h y s i c a l properties. A l s o i n T a b l e I V , b i s HHP sebacamide (11) shows commerc i a l l y viable stabilizing capabilities. The d i f u n c t i o n a l type o f s t r u c t u r e o f compound (11) and T i n u v i n 770 ( b i s ( 2 , 2 , 6 , 6 - t e t r a m e t h y l 4 - p i p e r i d i n y l ) d e c a n e d i o a t e ) may be a f a c t o r i n o p t i m i z i n g t h e a c t i v i t y of these a d d i t i v e s .


152

POLYMER STABILIZATION AND DEGRADATION


T a b l e I. Cone % 0.25 0.25 0.5 0.25 0.5

Initial

Additive (1) (2) (3) (4) (5)

Compatibility:

Compounds

Compatibility G G G G G

w/o L i f e t i m e 850 hours 900 2820 890 1320

G = Good, F = F a i r


12. RAMEY AND ROSTEK


Table I I ,


Cone % 0.25 0.25 0.25 0.25 0.25

Additive (6) (7) (8) (9) (10)

Intermediate

Compounds

Compatibility GG G G F


(10)

T a b l e I I L Hydroxybenzoate-HALS Cone % 0.25 0.25 0.25 0.25 0.25 0.25

Compound Chimassorb 994* T i n u v i n 622* IMZ (6) AM-340 AM-340 + 0.25 IMZ (6) T i n u v i n 770*

Interaction w/o L i f e t i m e 1970 hours 1750 1950 1350 2550 2460

*A11 a r e commercial HALS o f C i b a - G e i g y C o r p o r a t i o n UV-Chek AM-340 = Hydroxybenzoate s t a b i l i z e r of F e r r o C o r p o r a t i o n


154

POLYMER STABILIZATION AND DEGRADATION Table IV. Additive (11) (12) (13) (14) (15)

Compounds

Compatibility G G G G G



Cone % 0.25 0.25 0.25 0.25 0.25

Final

(16)


12.

RAMEY AND ROSTEK


155

Acknowledgments The authors wish to acknowledge the work of Dr. Goutam Gupta, who was the first to prepare HHP sebacamide and who also prepared the oxazolidines. We wish to thank, also, Dr. Ronald E. Thompson, who prepared the higher IMZ compounds, and Walter J . Wawro, Sr., who worked out the preparation of HHP by catalytic reduction.


Literature Cited 1.

Bagheri, R; Chakraborty, K.B.; Scott, G. Polym. Degrad. and Stab. 1982, 4, 1.

2.

Allen, N.S. Polym. Degrad. and Stab. 1980, 2, 179.

3.

Grattan, D.W.; Reddoch, A.H.; Carlsson, D . J . ; Wiles, D.M. J. Polym. S c i . , Polym. Lett. Ed. 1978, 16, 143.

4.

Hodgeman, D.K.C. J . Polym. S c i . , Polym. Chem. Ed. 1980, 18, 533.

5.

Carlsson, D.J.; Chan, K.H.; Wiles, D.M. J . Polym. S c i . , Polym. Lett. Ed. 1981, 19, 549.

6.

Carlsson, D . J . ; Chan, K.H.; Dumas, J.; Wiles, D.M. J.Polm. S c i . , Polym. Chem. Ed. 1982, 20, 575.

7.

Keana, J.D.W. Chem. Reviews 1978, 78(1), 37.

8.

Bailey, D; Vogl, O. J . Macromol. Sci-Rev. Macromol. Chem. 1976, C14(2), 267.

9.

Gupta, G.; Ramey, C.E. U.S. Patent 4, 404, 302, 1983.

10.

Matter, E. Helv. Chim. Acta

1947, 30, 1114-23.

11.

Ramey, C.E.; Rostek, C.J.

12.

Murayama, K.; Morimura, S.; Toda, T.; Akagi, S; Kurumada, T.; Watanabe, I. Ger. Offen. 1, 817, 703, 1969.

13.

Ferrini, P.; Marxer, A. Helv. Chim Acta 1963, Vol. XLVI, Fasc IV, 1207-1212.

U.S. Patent 4, 448, 969, 1984.

RECEIVED October 26, 1984


Hexahydropyrimidines as Hindered Amine Light Stabilizers - ACS

Recommend Documents