Radiation Curing of Polymeric Materials - American Chemical Society

Chapter 16

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Polymeric Coatings Containing Chlorendic Anhydride Decomposition Products of Chlorendic Anhydride John C. Graham and David J. Gloskey Coatings Research Institute, Eastern Michigan University, Ypsilanti, MI 48197

Chlorendic anhydride (4,5,6,7,8,8-hexachloro-3a,4,7,7a-tetrahydro-4,7-methanisobenzofuran1,3-dione, I, CAS registry number 115-27-5) has been used since 1964 in polyester coatings that can be cured under ultraviolet (UV) light. The presence of the chlorendic moiety in the polymeric backbone is observed to increase the curing rate of the polymer under these conditions, presumably because of the generation of CI radicals. In our studies, we have photolyzed chlorendic anhydride with and without photoinitiators in acetone and dioxane and examined the products generated by GC/MS procedure. The participation of these products in the rate of UV initiated curing of chlorendic containing polymeric coatings is discussed.

C h l o r e n d i c a n h y d r i d e (CAS R e g i s t r y No. 115-27-5) h a s been u s e d s i n c e 1964 i n t h e s y n t h e s i s o f UV c u r a b l e c o a t i n g s (1-12)• In previous s t u d i e s d e s i g n e d to evaluate the e f f e c t o f c h l o r e n d i c b a s e d d i l u e n t s on t h e r a t e o f c u r e and p h y s i c a l p r o p e r t i e s o f u l t r a v i o l e t (UV) c u r a b l e c o a t i n g s , two c h l o r e n d i c b a s e d r e a c t i v e d i l u e n t s ( I a n d I I ) were s y n t h e s i z e d a n d s u b s t i t u t e d i n p l a c e o f c o n v e n t i o n a l r e a c t i v e d i l u e n t s i n a c r y l a t e b a s e d UV c u r a b l e formulat i o n s (1_3) . The r e s u l t s , w h i c h a r e r e p r o d u c e d e l s e w h e r e (13.), show t h a t t h e a d d i t i o n o f t h e c h l o r e n d i c d i l u e n t s (I a n d I I ) i n c r e a s e d t h e r a t e o f c u r e , mar r e s i s t a n c e a n d p h y s i c a l p r o p e r t i e s o f UV c u r e d c o a t i n g s . Although the e n h a n c e d r a t e o f UV c u r e o b s e r v e d w i t h c h l o r e n d a t e based c o a t i n g s has been a s c r i b e d t o t h e c l e a v a g e o f c a r b o n c h l o r i n e bonds l e a d i n g t o a n i n c r e a s e i n t h e c o n c e n t r a tion o f f r e e r a d i c a l s ( 1 2 , 1 3 ) , no e x p e r i m e n t a l results 0097-6156/90/0417-0210$06.00/0 ©1990 American Chemical Society Hoyle and Kinstle; Radiation Curing of Polymeric Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

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GRAHAM & GLOSKEY

CI

211

OH -C0 CH CHCH 0 CC(CH3)CH 2

2

2

2

2

CClr •C0 CH ÇHCH 0 CC(CH3)CH 2

CÏ

J H Cl

2

2

2

2

OH

OH

I C0 CH CHCH 0 CCHCH 2

2

2

2

C0 CH CH 0 CCHCH 2

2

2

2

2

2

II

COCH(OC H ) 2

III

5

2

IV

a d d r e s s i n g t h i s i s s u e have been p u b l i s h e d , t o d a t e . In t h e s e s t u d i e s , we e x a m i n e d t h e p h o t o l y s i s o f c h l o r e n d i c a n h y d r i d e ( I I I ) i n a c e t o n e and d i o x a n e a s s o l v e n t s u s i n g d i e t h o x y a c e t o p h e n o n e ( I V ) a s t h e p h o t o i n i t i a t o r and GC/MS techniques to i d e n t i f y the p h o t o l y s i s products. Experimental Raw M a t e r i a l s . Chlorendic anhydride (III), acetone, and d i e t h o x y a c e t o p h e n o n e ( I V ) , were from c o m m e r c i a l s o u r c e s a n d u s e d , e x c e p t when i n d i c a t e d , without f u r t h e r p u r i f i c a t i o n .

dioxane, obtained otherwise

Photolysis Conditions. M o l e c u l a r s i e v e s were a d d e d t o the s o l v e n t s acetone and 1,4-dioxane, then d r y n i t r o g e n was b u b b l e d t h r o u g h t h e s o l v e n t s t o remove a n y d i s s o l v e d oxygen. F i n a l l y t h e s o l v e n t s were f i l t e r e d t o remove t h e molecular sieves. Chlorendic anhydride ( I I I ) ( l i t m.p. 2 3 5 - 2 3 9 ° C ) was r e c r y s t a l l i z e d f r o m h o t c h l o r o b e n z e n e , r i n s e d w i t h h e p t a n e a n d d r i e d a t 105°C. Diethoxyacetophenone ( I V ) was u s e d a s r e c e i v e d from t h e m a n u f a c t u r e r . The p h o t o l y s i s r e a c t i o n s were c a r r i e d o u t u s i n g an Ace G l a s s p h o t o c h e m i c a l r e a c t i o n v e s s e l (model #7841-03), q u a r t z immersion w e l l (model # 7 8 5 - 2 5 ) , Conrad-Hanovia power s u p p l y (model #7830-54), a n d C o n r a d - H a n o v i a immers i o n lamp (model #7825-32) r a t e d a t 200 w a t t s , 115-130 v o l t s , a n d 1.9 amps. The r e a c t i o n s o l u t i o n was p l a c e d i n t h e p h o t o c h e m i c a l r e a c t i o n v e s s e l and p u r g e d w i t h d r y n i t r o g e n . The p u r g e

Hoyle and Kinstle; Radiation Curing of Polymeric Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

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RADIATION CURING OF POLYMERIC MATERIALS

c o n t i n u e d t h r o u g h o u t t h e d u r a t i o n o f t h e e x p e r i m e n t (6 h o u r s o r 24 h o u r s ) . V o l a t i l e s were c o l l e c t e d b y p a s s i n g t h e p u r g e f l o w t h r o u g h a t r a p immersed i n a Dewar f l a s k f i l l e d with l i q u i d n i t r o g e n . T h e s o l u t i o n was g e n t l y s t i r r e d w i t h a m a g n e t i c s t i r r i n g b a r a n d t a p w a t e r was u s e d t o c o o l t h e medium p r e s s u r e m e r c u r y lamp. The tempe r a t u r e o f t h e s o l u t i o n was m a i n t a i n e d a t a p p r o x i m a t e l y room t e m p e r a t u r e d u r i n g t h e c o u r s e o f t h e r e a c t i o n . A f t e r t h e r e a c t i o n , s a m p l e s were t a k e n f r o m b o t h t h e r e a c t i o n v e s s e l a n d t h e t r a p a n d combined f o r GC/MS a n a lysis . I n s t r u m e n t a t i o n and Equipment. GC/MS a n a l y s i s was p e r formed u s i n g a F i n n i g a n 9610 g a s c h r o m a t o g r a p h e q u i p p e d w i t h a c a p i l l a r y column, a t a h e a d p r e s s u r e o f 10 p s i , w i t h a t e m p e r a t u r e ramp s e t a t 50°C f o r two m i n u t e s , t h e n a 20°C/min i n c r e a s e t o 275°C a n d h e l d a t 275°C u n t i l a l l t h e compounds h a d e l u t e d f r o m t h e c o l u m n . No d e t e c t o r ( i . e . F I D n o r TCD) was c o u p l e d t o t h e F i n n i g a n 4500 Mass Spectrometer ( t h e mass s p e c t r o m e t e r a c t e d a s t h e d e t e c tor). An e l e c t r o n i m p a c t i o n i z a t i o n s o u r c e w i t h an e l e c t r o n e n e r g y o f 70 eV a n d i o n i z a t i o n t e m p e r a t u r e o f 150°C was u s e d t o f r a g m e n t t h e compounds a s t h e y e l u t e d f r o m the column. R e s u l t s and D i s c u s s i o n The 24 h o u r p h o t o l y s i s o f c h l o r e n d i c a n h y d r i d e ( I I I ) i n a c e t o n e i n t h e p r e s e n c e o f d i e t h o x y a c e t o p h e n e (IV) y i e l d ed a t l e a s t t w e l v e m e a s u r a b l e p r o d u c t s a s o b s e r v e d by t h e GC/MS p r o c e d u r e ( T a b l e I ) . Some o f t h e p r o d u c t s o b s e r v e d , i . e . 4 - m e t h y l - 4 - h y d r o x y - 2 - p e n t a n o n e , b i a c e t a l , 4methyl-3-pentene-2-one, ethyl acetate, 3-methyl-3-hydroxy-2-butanone, 4-methyl-2-pentanone, and 2,4-pentaned i o n e , a r e c l e a r l y d e r i v e d from t h e p h o t o c h e m i c a l l y i n duced d e c o m p o s i t i o n o f acetone and/or diethoxyacetophenone . A l t h o u g h t h e compounds a n d p r e f e r r e d modes o f decomposition/recombination vary with the o v e r a l l systems, diethoxyacetophenone i n acetone e x h i b i t s p r i m a r i l y Norr i s h Type I c l e a v a g e a s e v i d e n c e d b y t h e f o r m a t i o n o f benzaldehyde, e t h y l benzoate, acetophenone and b e n z i l . A l t h o u g h a c e t a l y d e h y d e may i n d i c a t e N o r r i s h Type I I c l e a vage i s o b s e r v e d , i t i s l i k e l y t h a t t h i s compound i s d e r i v e d from t h e s o l v e n t and n o t t h e p h o t o i n i t i a t o r (Scheme 1)· However, i n t h e p r e s e n c e o f c h l o r e n d i c a n h y d r i d e , t h e decomposition of diethoxyacetophenone o c c u r s o n l y by N o r r i s h I type cleavage, y i e l d i n g benzoyl c h l o r i d e , acet o p h e n o n e a n d b e n z i l . No N o r r i s h Type I I c l e a v a g e p r o d u c t s were o b s e r v e d . The 24 h o u r p h o t o l y s i s o f c h l o r e n d i c anhydride i n acetone u s i n g diethoxyacetophenone as t h e p h o t o i n i t i a t o r shows c a r b o n - c h l o r i n e h o m o l y t i c bond cleavage and the g e n e r a t i o n o f c h l o r e n d i c r a d i c a l s as e v i d e n c e d by t h e a p p e a r a n c e o f b e n z o y l c h l o r i d e , c h l o r o -


16.

GRAHAM & GLOSKEY


Table I Summary and Comparison of Products Found A f t e r P h o t o l y s i s Using Acetone as the Solvent Acetone

Diethoxyacetophenone/ acetone

CA/acetone

4-methyl4-hydroxy2-pentanone

benzaldehyde ethylbenzoate


2-pentanone

acetophenone

acetic

biacetal

benzil

acetaldehyde

acetic

3-methyl3-hydroxy2-butanone

carbon dioxide propane

acid

acid

acetaldehyde

2-butanone

2-butanone

biacetal

2,4-pentanedione

ethyl acetate


2,4-pentanedione

ethyl acetate

4-methyl2-pentanone

3-methyl-3hydroxy-2butanone

4-methyl3-pentene2-one

diethoxyacetophenone

unknown chlorendic compound

Diethoxyacetophenone/ CA/acetone 4-methyl-3penten-2-one benzoyl chloride 4-methyl-2pentanone 3-methyl-3hydroxy2-butanone 4-methyl-4hydroxy2-pentanone chloroacetone 2,4-pentanedione biacetal

chlorendic anhydride

ethyl acetate unknown c h l o r endic compound unknown c h l o r endic compound chlorendic anhydride


213


214

N o r r i s h Type I

Ο

II

C

H

2 5*

+

H C 0

C

H

2 2 5

N o r r i s h Type I I

Scheme 1.

P h o t o l y t i c d e c o m p o s i t i o n pathways o f diethoxyacetophenone.


16.

GRAHAM & GLOSKEY


a c e t o n e and two unknown c h l o r e n d i c compounds where c h l o r i n e atoms have been r e p l a c e d by h y d r o g e n atoms. Since o n l y one c h l o r e n d i c compound was o b s e r v e d i n t h e p r o d u c t m i x t u r e o b t a i n e d from t h e 24 h o u r p h o t o l y s i s o f c h l o r e n d i c anhydride i n acetone, i t i s proposed that the presence o f d i e t h o x y a c e t o p h o n e i n acetone as the s o l v e n t , e n h a n c e s c a r b o n - c h l o r i n e bond c l e a v a g e . The UV spectra o f c h l o r e n d i c a n h y d r i d e shows a b s o r p t i o n maxima a t 272 and 286 NM w h i c h c l o s e l y c o r r e s p o n d s t o t h e UV s p e c t r a l e m i s s i o n o f t h e lamp i n d i c a t i n g t h a t c h l o r e n d i c a n h y d r i d e i s c a p a b l e o f h o m o l y t i c c h a i n c l e a v a g e i n the absence o f photoinitiators. U s i n g d i o x a n e as t h e s o l v e n t ( T a b l e I I ) , a s i m i l a r s i t u a t i o n i s observed with the decomposition o f d i e t h o x y a c e t o p h e n o n e o c c u r i n g by N o r r i s h Type I c l e a v a g e as e v i d e n c e d by t h e f o r m a t i o n o f e t h y l f o r m a t e , b e n z o y l c h l o r i d e and a c e t o p h e n o n e w i t h no e v i d e n c e f o r N o r r i s h Type II cleavage. E v i d e n c e f o r h y d r o g e n a b s t r a c t i o n from t h e dioxane molecule i s observed i n the g e n e r a t i o n of dioxane d i m e r s and c h l o r o d i o x a n e . A l t h o u g h t h e f o r m a t i o n o f c h l o r o d i o x a n e and b e n z o y l c h l o r i d e c a n be j u s t i f i e d on t h e b a s i s o f a h o m o l y t i c d i s p l a c e m e n t mechanism, t h e p r e s e n c e o f a t l e a s t t h r e e c h l o r e n d i c b a s e d m o l e c u l e s where one o r two c h l o r i n e s have b e e n l o s t f r o m c h l o r e n d i c a n h y d r i d e and r e p l a c e d by h y d r o g e n atoms c l e a r l y i n d i c a t e s homol y t i c c l e a v a g e and t h e g e n e r a t i o n o f c h l o r i n e r a d i c a l s . S i m i l a r l y , c h l o r e n d i c compounds were o b s e r v e d i n t h e p h o t o l y s i s o f c h l o r e n d i c a n h y d r i d e i n d i o x a n e and i t a p p e a r s t h a t d i e t h o x y a c e t o p h e n o n e may have l e s s i n f l u e n c e i n the g e n e r a t i o n of products i n dioxane than i n acetone. U n l i k e c h l o r e n d i c a n h y d r i d e w h e r e t h e MS s h o w s a f r a g m e n t a t i o n p a t t e r n i n v o l v i n g t h e s e q u e n t i a l l o s s o f CI (m/e = 3 5 ) , CO (m/e = 2 8 ) , C 0 (m/e = 4 4 ) , and C « H (m/e = 26) as w e l l as t h e r e v e r s e D i e l - A l d e r f r o m t h e m o l e c u l a r i o n p e a k (m/e = 368) a c c o u n t i n g f o r t h e h i g h e r m o l e c u l a r w e i g h t f r a g m e n t s (Scheme 2 ) , t h e unknown c h l o r e n d i c compounds show f r a g m e n t a t i o n p a t t e r n s c o n s i s t e n t w i t h t h e l o s s o f c h l o r i n e f r o m t h e s t a r t i n g m a t e r i a l and r e p l a c e m e n t by h y d r o g e n atoms i n b o t h s o l v e n t s u s e d . A t y p i c a l compound o b s e r v e d i n t h e c a s e where d i o x a n e i s u s e d as t h e s o l v e n t shows t h e MS f r a g m e n t a t i o n p a t t e r n o u t l i n e d i n Scheme 3. 2

2

Conclusions Our f i n d i n g s c l e a r l y show t h a t c h l o r e n d i c a n h y d r i d e and presumably polymers c o n t a i n i n g the c h l o r e n d a t e group a r e c a p a b l e , u n d e r UV l i g h t , o f u n d e r g o i n g m u l t i p l e c a r b o n c h l o r i n e bond c l e a v a g e g e n e r a t i n g c h l o r i n e and c a r b o n radicals. The p r e s e n c e o f t h e s e r a d i c a l s , by i n c r e a s i n g the c o n c e n t r a t i o n of f r e e r a d i c a l s i n the system, a r e c a p a b l e o f i n c r e a s i n g t h e r a t e o f r e a c t i o n and c r o s s l i n k ing of UV c u r a b l e c o a t i n g s c o n t a i n i n g the chlorendic


216


Table I I Summmary and Comparison of Products Found A f t e r P h o t o l y s i s Using Dioxane as the Solvent

Diethoxyacetophenone/ Dioxane

CA/Dioxane

Diethoxyacetophenone/ CA/Dioxane

e t h y l formate

hydroxydioxane

ethyl

e t h y l dioxane

chlorodioxane

hydroxydioxane

diethoxymethane

d i o x a n y l dioxane

chlorodioxane

(2 isomers)

benzoyl

formate

chloride

benzoic a c i d CA - 3 C l + 2H

d i o x a n y l dioxane

l-phenyl-2ethoxyethanone

CA - 2 C l + H

(2 isomers)

benzaldehyde

CA - C l + H

acetophenone

chlorendic anhydride

CA - C l + H CA - C l + H CA - 2 C l + H chlorendic anhydride


16.

GRAHAM & GLOSKEY

m/e = 270


m/e = 235

217

m/e = 261 (BP)

Scheme 2. MS Fragmentation Pattern for Chlorendic Anhydride



218

m/e = 334

(m/e 98)

m/e = 299

-C H 0 4

2

3

(m/e 98)

m/e = 255

-CO

(m/e 28)

Scheme 3. MS A n a l y s i s o f One o f t h e C h l o r e n d i c B a s e d P h o t o p r o d u c t s When D i o x a n e i s U s e d a s t h e S o l v e n t


16.


GRAHAM & GLOSKEY

moiety. T h i s w i l l r e s u l t i n much f a s t e r rate of cure ( c r o s s - l i n k i n g ) s e l v e s and o t h e r s .

h a r d e r c o a t i n g s and as o b s e r v e d by o u r

Acknowledgment The a u t h o r s a r e g r a t e f u l t o V e l s i c o l f o r t h e i r s u p p o r t o f t h i s work.

Chemical C o r p o r a t i o n

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

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et

al.

U.S.

Patent

4 591

522,

1986.

RECEIVED September 13, 1989


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