Polymeric Materials for Corrosion Control - ACS Publications

9 Degradation of Organic Protective Coatings on Steel Downloaded by PRINCETON UNIV on August 11, 2015 | http://pubs.acs.org Publication Date: October 14, 1986 | doi: 10.1021/bk-1986-0322.ch009

Tinh Nguyen and W. Eric Byrd Building Materials Division, National Bureau of Standards, Gaithersburg, M D 20899

The application of reflection/absorption Fourier transform infrared spectroscopy (FTIR-RA) for studying the degradation of two types of coatings on steel after exposure to an 40°C/80% RH environment is presented in this paper. FTIR-RA results indicate the occurrence of bond weakening, dehydration and bond scissions of amine-cured epoxy after exposure. On the other hand, the polybutadiene coating shows not only bond weakening but also extensive degradation which results in the formation of various oxidized products and losses in unsaturation. The characterization of complex molecules formed during the oxidation and degradation by FTIR-RA offers a powerful means for studying the degradation processes of protective coatings on steel.

M e t a l l i c c o r r o s i o n i s e s t i m a t e d t o c o s t the U.S. more than $100 b i l l i o n a n n u a l l y (1)· P o l y m e r i c c o a t i n g s are w i d e l y used t o p r o l o n g the s e r v i c e l i f e o f c o r r o s i o n - p r o n e s u b s t r a t e s . However, t h e s e c o a t i n g s can undergo p h y s i c a l and c h e m i c a l changes under s e r v i c e c o n d i t i o n s t h a t reduce t h e i r e f f e c t i v e n e s s . Chemical changes w h i c h o c c u r a t the m e t a l / c o a t i n g i n t e r f a c e a r e p a r t i c u l a r l y i m p o r t a n t i n the d e g r a d a t i o n p r o c e s s e s . P a r t o f our o v e r a l l t a s k i n p r e d i c t i n g the s e r v i c e l i f e o f p r o t e c t i v e c o a t i n g s i s t o g a i n a b e t t e r u n d e r s t a n d i n g o f the d e g r a d a t i o n mechanisms l e a d i n g t o a d h e s i o n f a i l u r e and t o c o r r o s i o n o f the p r o t e c t e d m e t a l beneath the c o a t i n g . F o u r i e r t r a n s f o r m i n f r a r e d s p e c t r o s c o p y has been shown t o be a n e x c e l l e n t t o o l f o r s u r f a c e and i n t e r f a c e s t u d i e s ( 2 ) . I n t h i s paper, the a p p l i c a t i o n o f r e f l e c t i o n / a b s o r p t i o n F o u r i e r t r a n s f o r m i n f r a r e d s p e c t r o s c o p y (FTIR-RA) f o r s t u d y i n g the d e g r a d a t i o n o f amine-cured epoxy and p o l y b u t a d i e n e c o a t i n g s on c o l d - r o l l e d s t e e l a f t e r exposure t o a warm, humid environment i s r e p o r t e d . This chapter not subject to U.S. copyright. Published 1986, American Chemical Society

In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

POLYMERIC MATERIALS FOR CORROSION CONTROL

102 EXPERIMENTAL

Downloaded by PRINCETON UNIV on August 11, 2015 | http://pubs.acs.org Publication Date: October 14, 1986 | doi: 10.1021/bk-1986-0322.ch009

Materials The amine-cured epoxy used was from a f o r m u l a t i o n c o n t a i n i n g : 100 p a r t s o f epoxy r e s i n (Epon 1001, S h e l l Chemical Co.), 6 p a r t s o f d i e t h y l e n e t r i a m i n e , and 3 p a r t s o f b u t y l a t e d u r e a formaldehyde ( f l o w - c o n t r o l l e d a g e n t ) . A l l components were a t 12.5% i n g l y c o l e t h e r / x y l e n e (50/50, w/w) s o l u t i o n s . The epoxy and f l o w - c o n t r o l l e d agent were premixed t o g e t h e r as the base component, w h i c h was mixed w i t h the c u r i n g agent j u s t b e f o r e c o a t i n g . The p o l y b u t a d i e n e was Budium RKY662 (Dupont) i n p e t r o l e u m d i s t i l l a t e s o l v e n t . The c o l d - r o l l e d s t e e l samples were low-carbon SAE 1010, o f the s i z e 25 χ 25 χ 0.8 mm. (Trade names are g i v e n s o l e l y t o i n d i c a t e e x p e r i m e n t a l m a t e r i a l s and equipment used and not t o recommend a p a r t i c u l a r product). Specimen P r e p a r a t i o n S t e e l s u b s t r a t e s were m e c h a n i c a l l y p o l i s h e d ( f i n a l p o l i s h i n g was w i t h a lym diamond p a s t e ) , r i n s e d r e p e a t e d l y w i t h w a t e r and m e t h a n o l , blown dry w i t h hot a i r , and s t o r e d i n a d e s i c c a t o r b e f o r e use (but not more than 3 d a y s ) . The d r i e d s u b s t r a t e specimens were immersed i n methanol f o r 2 h o u r s , then washed w i t h acetone i m m e d i a t e l y p r i o r t o a p p l y i n g the c o a t i n g s . Both methanol and acetone were ACS grade r e a g e n t s . The c o a t i n g s were a p p l i e d by f l o o d i n g the s u b s t r a t e w i t h r e s i n s o l u t i o n s and s p i n n i n g them h o r i z o n t a l l y a t 3500 RPM f o r 30 s u s i n g a p h o t o r e s i s t s p i n n e r . Initial f i l m t h i c k n e s s e s o f 1.8ym f o r the epoxy and o f 2.0μπι f o r the p o l y butadiene were measured u s i n g a s c a n n i n g s p e c t r o s c o p i c r e f l e c t e d l i g h t m i c r o s c o p e . The unaged FTIR-RA s p e c t r a were c o l l e c t e d a f t e r c u r i n g f o r 3 weeks a t room c o n d i t i o n s . A l l specimens were t h e n exposed i n a 40°C and 80% RH chamber. Aged samples were removed from the chamber a t v a r i o u s time i n t e r v a l s f o r IR a n a l y s i s . F i l m t h i c k n e s s e s o f the aged samples were not measured. FTIR-RA S p e c t r a S p e c t r a were o b t a i n e d u s i n g a 60 SX N i c o l e t FTIR s p e c t r o m e t e r and a Barnes v a r i a b l e a n g l e s p e c u l a r r e f l e c t i o n a c c e s s o r y . The s p e c t r o m e t e r was equipped w i t h a n i t r o g e n - c o o l e d mercury cadmium t e l l u r i d e d e t e c t o r and was c o n s t a n t l y purged w i t h d r y a i r t o m i n i m i z e the e f f e c t o f m o i s t u r e . The i n s t r u m e n t was a l s o equipped w i t h a l a s e r i n t e r f e r o m e t e r t o i n s u r e wave l e n g t h a c c u r a c y . A l l spectra were the r e s u l t o f 1000 c o - a d d i t i o n s and t a k e n a t 4 cm" r e s o l u t i o n u s i n g s i n g l e r e f l e c t i o n a t an i n c i d e n t angle o f 45 d e g r e e s . A l l s p e c t r a a r e shown i n the absorbance mode and have been r a t i o e d a g a i n s t the spectrum o f a s i l v e r r e f e r e n c e m i r r o r . 1

RESULTS AND DISCUSSIONS Degradation

o f Amine-Cured Epoxy C o a t i n g on C o l d - R o l l e d S t e e l

FTIR-RA s p e c t r a o f the amine-cured epoxy c o a t i n g on c o l d - r o l l e d s t e e l b e f o r e and a f t e r exposure a t 40°C and 80% RH a r e shown i n


9.

Degradation of Organic Protective Coatings on Steel

NGUYEN AND BYRD

F i g u r e 1. The assignments o f FTIR-RA s p e c t r a o f unaged epoxy f r e e and coated f i l m s on s t e e l have been g i v e n p r e v i o u s l y ( 3 ) . I t s h o u l d be noted t h a t t h i s aged specimen e x h i b i t e d e x t e n s i v e f i l i f o r m c o r r o s i o n a f t e r 7 months exposure. F i g u r e s 2 show t h e s p e c t r a l changes a t d i f f e r e n t exposure p e r i o d s . These s p e c t r a have been n o r m a l i z e d f o r t h e b a s e l i n e s h i f t r e s u l t i n g from t h e r e f l e c t i o n change o f t h e s t e e l s u b s t r a t e due t o exposure and c o r r o s i o n . F i g u r e 2a shows t h a t a g i n g o f amine-cured epoxy i n t h e t e s t e n v i r o n ment r e s u l t e d i n a s h i f t t o h i g h e r f r e q u e n c y o f t h e OH maximum a t 3401 c m and an i n c r e a s e i n i n t e n s i t i e s o f t h e band a t 3560 cm"" . Chen e t a l . , ( 4 ) a l s o noted a s h i f t t o h i g h e r f r e q u e n c y due t o t h e r m a l d e g r a d a t i o n o f t h e OH band i n t r i m e t h o x y b o r o x i n e cured epoxy c o a t i n g on aluminum. On t h e o t h e r hand, H a r r o d ( 5 ) o b s e r v e d p r o g r e s s i v e s h i f t s t o h i g h e r frequency o f t h e OH band maxima o f amine-cured epoxy w i t h i n c r e a s i n g temperature and a t t r i buted t h e s h i f t t o t h e change from l o n g range t o s h o r t range Η-bonding o f b o t h t h e O-H Ν and O-H 0 t y p e s . FTIR-RA s t u d i e s of t h i n f i l m s on s t e e l and f r e e f i l m s ( 6 ) i n d i c a t e d t h a t t h e r e i s no s t r o n g i n t e r a c t i o n between t h e amine-cured epoxy and t h e s t e e l s u b s t r a t e . Thus, t h e s h i f t t o h i g h e r frequency o f t h e OH maximum a t 3401 cm"" o f amine-cured epoxy on s t e e l exposed t o a c o r r o s i v e environment i s a t t r i b u t e d t o t h e weakening o f t h e Η-bonds w i t h i n the epoxy c o a t i n g i t s e l f . The i n t e n s i t y i n c r e a s e a t t h e 3560 cm"" band i n d i c a t e d t h a t n o n a s s o c i a t e d OH groups were formed d u r i n g exposure. The bands a t 1041 and 1085 c m (C-0 s t r e t c h i n g ) broadened and i n c r e a s e d i n i n t e n s i t y ( F i g u r e 2c) i n d i c a t i n g t h e f o r m a t i o n o f more - 1


1

1

1

- 1

I

1

1

1

4000

3600

3200

2800

1

2400

1

2000

1

1

1

1

1600

1200

800

400

WAVENUMBERS

F i g u r e 1. FTIR-RA s p e c t r a o f amine-cured epoxy c o a t i n g on c o l d - r o l l e d s t e e l b e f o r e and a f t e r exposure t o 40°C and 80% RH


103


104


I

3725

I

I

I

I

3600

3475

3350

3225

I

I

Γ

3100

1550

I

1525 1500

WAVENUMBERS

I

I

I

I

I

1250

1210

1170

1130

1090

I

I

I

1050 1010

WAVENUMBERS

F i g u r e 2. N o r m a l i z e d FTIR-RA s p e c t r a o f amine-cured epoxy c o a t i n g on c o l d - r o l l e d s t e e l exposed t o 40°C and 80% RH f o r d i f f e r e n t t i m e s . Reproduced, w i t h p e r m i s s i o n , from Ref. 3


9.

N G U Y E N A N D BYRD


OH groups d u r i n g exposure. D e s p i t e the g r a d u a l i n c r e a s e i n the C-0 r e g i o n and the r e d u c t i o n of the epoxide groups (915 cm" band) t o form OH, the i n t e n s i t y i n the OH r e g i o n remains unchanged. T h i s i s p r o b a b l y due t o d e h y d r a t i o n , e i t h e r t h r o u g h c h e m i c a l r e a c t i o n or l o s s of sorbed w a t e r . D e h y d r a t i o n has been i d e n t i f i e d as the major r e a c t i o n and water has been i d e n t i f i e d as a major p r o d u c t of the d e g r a d a t i o n at low temperatures of amine-cured epoxy (7,8)· The d e c r e a s e s i n the i n t e n s i t i e s of the bands a t 1516 cm" (OC of the benzene r i n g ) and 1179 cm" (C-C s t r e t c h i n g of i s o p r o p y l i d e n e ) suggest t h a t the b i s p h e n o l - A s t r u c t u r e of the c o a t e d epoxy has degraded as w e l l . The presence of Ν i n the cured epoxy makes i t v e r y s u s c e p t i b l e t o n u c l e o p h i l i c c h a i n b r e a k i n g and a l l y l - N bond s c i s s i o n s ; b o t h of t h e s e r e a c t i o n s r e s u l t i n l o s s of the a r o m a t i c r i n g s ( 7 , 1 0 ) . On the o t h e r hand, the l o s s of i s o p r o p y l i d e n e group may be e x p l a i n e d by i t s low bond energy ( 8 ) . A l t h o u g h t h i s group i s more s t a b l e than the cure l i n k a g e i n amine-cured epoxy ( 9 ) , i t i s the l e a s t s t a b l e group i n a n h y d r i d e - c u r e d epoxy, and undergoes d e g r a d a t i o n d u r i n g e a r l y d e c o m p o s i t i o n ( 8 ) . There i s a l s o a n o t i c e a b l e i n c r e a s e i n i n t e n s i t y of the a r y l - 0 band a t 1223 cm" , e s p e c i a l l y i n the e a r l y a g i n g s t a g e s . T h i s i n d i c a t e s some a s s o c i a t i o n , p r o b a b l y t h r o u g h Η-bonding, between the Ν or OH group and the p h e n y l e t h e r . I t i s known t h a t i n t e r a c t i o n not o n l y s h i f t s the f r e q u e n c y but a l s o i n c r e a s e s the i n t e n s i t i e s of an IR band (11) · The a s s o c i a t i o n between Ν and 0 was e v i d e n c e d by IR s p e c t r o s c o p y (12) and the i n t e n s i t y i n c r e a s e of the 1240cm" 1

1


1

1

1

Τ

I 4000

1

3600

1

1

1

1

1

1

I 3200

I 2800

ι 2400

ι 2000

ι 1600

1200

I

Γ

» 800

WAVENUMBERS

F i g u r e 3. FTIR-RA s p e c t r a of p o l y b u t a d i e n e c o a t i n g on c o l d r o l l e d s t e e l b e f o r e and a f t e r exposure t o 40°C and 80% RH


I 400

105

106


band o f a n h y d r i d e - c u r e d epoxy exposed t o m o i s t u r e was a t t r i b u t e d t o the i n t e r a c t i o n o f water m o l e c u l e s w i t h t h e p h e n y l e t h e r ( 1 3 ) . D e g r a d a t i o n o f P o l y b u t a d i e n e C o a t i n g on C o l d - R o l l e d S t e e l FTIR-RA s p e c t r a o f a i r - c u r e d p o l y b u l a d i e n e c o a t i n g on c o l d - r o l l e d s t e e l b e f o r e and a f t e r exposure t o a 40°C and 80% RH environment a r e p r e s e n t e d i n F i g u r e 3· The c o m p o s i t i o n o f t h i s p o l y b u t a d i e n e and t h e assignments o f i t s FTIR-RA s p e c t r a were p r e s e n t e d elsewhere ( 3 ) . E x t e n s i v e c o r r o s i o n was observed i n t h e 7-month exposed specimen. The c u r e d b u t unaged specimen o x i d i z e d e x t e n s i v e l y , as e v i d e n c e d by t h e presence o f OH groups i n t h e 3150-3650 cm"" r e g i o n and c a r b o n y l groups i n t h e 1650-1800 cm" r e g i o n . The n o r m a l i z e d s p e c t r a ( F i g u r e 4) show c o n s i d e r a b l e changes i n t h e p o l y b u t a d i e n e c o a t i n g r e s u l t i n g from t h e exposure. The maximum o f t h e OH s t r e t c h i n g (3150-3650 cm" ) s h i f t e d t o h i g h e r f r e q u e n c y as a r e s u l t o f exposure ( F i g u r e 4 a ) , and t h i s was a t t r i b u t e d t o t h e weakening o f the Η-bonds o f t h e c o a t i n g system ( 3 ) . S h i f t s o f s m a l l e r magnitude were observed f o r t h e C-0 bending band a t 582 cm" ( F i g u r e 3 ) . The i n t e n s i t i e s o f t h e bands a t 1182 cm" ( e s t e r C-0) and 1060 cm" ( a l c o h o l C-0) i n c r e a s e d and t h e l a t t e r a l s o broadened con s i d e r a b l y as exposure time i n c r e a s e d ( F i g u r e 4 d ) . T h i s i n d i c a t e s the f o r m a t i o n o f more and v a r i e d C-0 c o n t a i n i n g p r o d u c t s d u r i n g exposure. I n c o n s t r a s t , t h e OH s t r e t c h i n g i n t e n s i t i e s i n c r e a s e i n the e a r l y exposure s t a g e , t h e n l e v e l o f f . These r e s u l t s suggest t h a t O H - c o n t a i n i n g compounds, such as a l c o h o l s , were formed i n t h e e a r l y s t a g e s o f exposure. These p r o d u c t s c o n t i n u e t o form i n t h e l a t e r exposure p e r i o d s but some o f them a r e c o n v e r t e d t o h i g h l y o x i d i z e d p r o d u c t s , such as e s t e r s and l a c t o n e s as e v i d e n c e d by t h e bands a t 1737 and 1775 cm" , r e s p e c t i v e l y . These compounds a r e known as common p r o d u c t s found i n t h e o x i d a t i v e d e g r a d a t i o n s o f PBD (14,15). The most n o t i c e a b l e changes o f t h e p o l y b u t a d i e n e c o a t i n g on s t e e l s u b j e c t e d t o the warm, humid environment a r e observed i n t h e complex 1600-1800 cm" r e g i o n ( F i g u r e 4 b ) . Numerous new peaks appeared and t h e i n t e n s i t i e s o f e x i s t i n g peaks changed as a r e s u l t of exposure. The assignments o f t h e s e peaks were a l r e a d y g i v e n ( 3 ) . The bands a t 1573 and 1581 cm" a r e p r o b a b l y due t o c a r b o x y l a t e i o n s . V a r i o u s peaks i n t h e r e g i o n s between 1610 and 1660 cm" a r e p r o b a b l y a s s o c i a t e d w i t h t h e C=C bonds. The bands i n t h e r e g i o n between 1680 and 1780 c m a r e a s s o c i a t e d w i t h t h e f o r m a t i o n o f u n s a t u r a t e d and s a t u r a t e d 0 0 groups ( 3 , 1 4 ) . C o n s i d e r a b l e l o s s e s o f t h e u n s a t u r a t i o n were a l s o o b s e r v e d , as e v i d e n c e d by t h e d e c r e a s e s i n i n t e n s i t i e s o f t h e bands a t 974 cm"" (CH o u t - o f - p l a n e bending o f t r a n s -CH=CH-), 911 cm"" ( C H o u t - o f p l a n e bending o f -CH=CH ). 2931 and 2865 cm" (CH and C H s t r e t c h i n g ) , and 1360 cm" ( C H wag). A d d i t i o n a l e v i d e n c e from IR a n a l y s i s a t o t h e r exposure p e r i o d s i n d i c a t e t h a t most o f t h e l o s s e s o f the u n s a t u r a t i o n i n t h e e a r l y s t a g e s o f d e g r a d a t i o n o c c u r a t t h e end v i n y l group. T h i s i s i n agreement o f w i t h an e a r l y o b s e r v a t i o n (14) t h a t under o x i d a t i v e d e g r a d a t i o n a t 130°C f o r 20 m i n u t e s , p o l y b u t a d i e n e l o s e s i t s u n s a t u r a t i o n i n t h e c i s -CH=CH- and -CH=CH but n o t t r a n s -CH=CH- group. The l o s s o f u n s a t u r a t i o n o f PBD i s a l s o due t o c r o s s l i n k i n g as e v i d e n c e d i n t h i s s t u d y by t h e e x t e n s i v e c r a z i n g on t h e s u r f a c e o f t h e c o a t e d 1


1

1

1

1

1

1

1

1

1

- 1

1

1

2

1

2

2

1

2

2



NGUYEN AND BYRD


9.

τ

1

I

I

I

I

I

I

1860

1820

1780

1740

1700

1660

1620

_]

1

1

1

1

1

Γ

I

1

1580 1540

WAVENUMBERS F i g u r e 4 a and b. N o r m a l i z e d FTIR-RA s p e c t r a o f p o l y b u t a d i e n e c o a t i n g on c o l d - r o l l e d s t e e l exposed t o 40 °C and 80% RH f o r d i f f e r e n t t i m e s . Reproduced w i t h p e r m i s s i o n from r e f e r e n c e 3.


107

108



τ

1

1

1

1

I

I

I

I

I

I

1505

1470

1435

1400

1365

1330

1

Γ

I

U

1295 1260

WAVENUMBERS

Τ

I

1275

1

974

1

ι

1

ι

ι

ι

ι

I

I

1

1220

1165

1110

1055

1000

945

890

d

L_

835

WAVENUMBERS

F i g u r e 4 c and d. N o r m a l i z e d FTIR-RA s p e c t r a o f p o l y b u t a d i e n e on c o l d - r o l l e d s t e e n exposed t o 40 °C and 807 RH f o r d i f f e r e n t Reproduced w i t h p e r m i s s i o n from r e f e r e n c e 3. o


coating times.

9.

NGUYEN AND BYRD


specimens. K a g i y a and Takemoto (16) c o r r e l a t e the l o s s o f s o l u b i l i t y (due t o c r o s s l i n k i n g ) o f a i r - i r r a d i a t e d PBD w i t h the i n c r e a s e of methylene groups and e t h e r l i n k a g e s . T h i s i s i n agreement w i t h F i g u r e 4c w h i c h shows an i n c r e a s e o f the band c e n t e r e d a t 1446 c m (CH2 bending) w i t h i n c r e a s i n g time f o r s h o r t exposure p e r i o d s ; the d e c r e a s e a t the l a t e r stage i s due t o c h a i n s c i s s i o n . - 1


CONCLUSIONS FTIR-RA a n a l y s e s o f amine-cured epoxy and p o l y b u t a d i e n e c o a t i n g s on c o l d - r o l l e d s t e e l exposed t o 40°C and 80% RH environments f o r 7 months i n d i c a t e bond weakening, d e h y d r a t i o n and bond s c i s s i o n s o f amine-cured epoxy d u r i n g exposure. On the o t h e r hand, the p o l y butadiene c o a t i n g specimens show bond weakening and e x t e n s i v e d e g r a d a t i o n w h i c h r e s u l t s i n the f o r m a t i o n o f v a r i o u s o x i d i z e d p r o d u c t s and l o s s e s i n u n s a t u r a t i o n . The c h a r a c t e r i z a t i o n o f complex m o l e c u l e s t h a t a r e formed d u r i n g the o x i d a t i o n and d e g r a d a t i o n by FTIR-RA o f f e r s a p o w e r f u l means f o r s t u d y i n g t h e d e g r a d a t i o n p r o c e s s e s o f p r o t e c t i v e c o a t i n g s on s t e e l .

LITERATURE CITED 1. 2. 3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

Bennett, L. H . , et a l . NBS Special Publication 1978, 511-1. Nguyen, T. Prog. Org. Coat. 1985, 13, 1. Nguyen, T . ; Byrd, W. E. Proc. XI Int. Conf. Org. Coat. Sci. Technol., 1985, p. 235. Chen, C. S.; Bulkin, B. J.; Pearce, E. M. J. Appl. Polym. Sci. 1983, 28, 1077. Harrod, J. F. J. Polym. Sci. 1963, A1, 385. T. Nguyen and E. Byrd, FTIR-RA spectral characteristics of epoxy coatings on cold-rolled steel; effects of film thickness and angle of incidence, Appl. Spectrosc. submit for publication, 1985. Paterson-Jones, J . C. J. Appl. Polym. Sci. 1975, 19, 1539 . Lin, S. L.; Bulkin, B. J.; Pearce, E. M. J. Polym. Sci. Polym. Chem. ed., 1979, 17, 3121. Bishop, D. P.; Smith, D. A. Ind. Eng. Chem. 1967, 59, 33. Paterson-Jones, J . C.; Percy, V. Α.; Giles, R. G. F . ; Stephen, A. M. J . Appl. Polym. Sci. 1973, 17, 1877. Hadzi, D.; Bratos, S., in "The Hydrogen Bond-Recent Developments in Theory and Experiments"; Schuster, P., et. a l . , Eds; North-Holland: Amsterdam, 1976, pp. 567-611. Dannenberg, H. SPE Trans. 1963, 3, 78. Antoon, M. K.; Koenig, J . L. J. Polym. Sci. Polym. Phys. Ed. 1981, 19, 1567. Beavan, S. W.; Phillips, D. Rubber Chem. Technol. 1975, 48, 692. Pecsok, R. L.; Painter, P. C.; Shelton, J . R.; Koenig, J . L. Rubber Chem. Technol. 1976, 49, 1010. Kagiya, V. T . ; Takemoto, K. J . Macromol. Sci.-Chem. 1976, A10, 795.

RECEIVED February 3, 1986


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