Polymeric Materials for Corrosion Control - American Chemical Society

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Polyurethane Foam Component Lifetimes Κ. B . Wischmann Sandia National Laboratories, Albuquerque, ΝM 87185

Access deterrent foams are generated by mixing two sep arately stored and pressurized components upon demand. Investigations have been conducted concerning the aging of both components of three separate polyurethane foam formulations. The polyol component of the first formu lation, a propylene oxide adduct of phosphoric acid, hydrolyzes rapidly to give phosphoric acid. Since phosphoric acid can corrode the container as well as adversely affect the final foam properties, a second formulation not containing acid adduct was investi gated. This second polyol was isothermally aged at room temperature, 60°C and 71°C and reactions followed by acid number determination. A reaction between the polyol and the blowing agent, Freon 11, was found to give high acid content. Attempts to add inhibitors to lengthen this initiation period failed. Finally, a third formulation was designed which placed the Freon 11 in the isocyanate component thereby precluding the incompatibility of the blowing agent with the polyol. Subsequent aging studies indicate a long term (6-8 years) storage foam system could be achieved. *This work was performed at Sandia National Laboratories supported by the U. S. Department of Energy under Contract Number DE-AC04-76DP00789. S t o r e d prepacked p o l y u r e t h a n e foam components, e.g., i s o c y a n a t e , p o l y o l s , a r e prone t o c h e m i c a l a g i n g , thereby j e o p a r d i z i n g t h e i r i n tended f u n c t i o n . I n f a c t , many vendors o f these Freon blown m a t e r i a l s w i l l n o t guarantee t h e i r product f o r more than 90 days. This i s f o r a v a r i e t y o f reasons such as m o i s t u r e a t t a c k on t h e i s o c y a n a t e , b l o w i n g agent s e p a r a t i o n and g e n e r a l m a t e r i a l i n s t a b i l i t y , e.g., t h e r m a l d e g r a d a t i o n , i n c o m p a t i b i l i t y . Because o f t h e expense t o change-out foam components, we would l i k e our systems t o l a s t as l o n g as p o s s i b l e . A l t h o u g h g e n e r a l l y c o n s i d e r e d c h e m i c a l l y i n e r t , Freon 11 ( t r i 0097-6156/ 86/ 0322-0341 $06.00/ 0 © 1986 American Chemical Society

Dickie and Floyd; Polymeric Materials for Corrosion Control ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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POLYMERIC MATERIALS FOR CORROSION CONTROL

c h l o r o f l u o r o m e t h a n e , CCI3F), the b l o w i n g agent used i n these foams, i s u n s t a b l e under c e r t a i n c o n d i t i o n s - For example, t h i s p o p u l a r i n d u s t r i a l r e f r i g e r a n t and a e r o s o l , i n the presence o f m o i s t u r e , w i l l r e a c t w i t h s t e e l o r aluminum f o r m i n g f r e e h y d r o c h l o r i c a c i d (1_,2)« As a r e s u l t , e f f o r t s a r e made t o m a i n t a i n anhydrous c o n d i t i o n s o r provide a c i d scavengers. A l t h o u g h not w i d e l y known, Freon 11 w i l l r e a c t w i t h p r i m a r y and secondary a l c o h o l s i n c l u d i n g p o l y o l s t o l i b e r a t e a l d e h y d e s , ketones and h y d r o c h l o r i c a c i d C3>^)* A l l the above mentioned r e a c t i o n s can be a c c e l e r a t e d w i t h temperature. At h i g h e r temperatures t h e r m a l d e c o m p o s i t i o n o f Freon 11 may produce h y d r o c h l o r i c a c i d ( 5 ) . E f f o r t s have been made t o f i n d s u i t a b l e s t a b i l i z e r s f o r t h i s f l u o r o c a r b o n ; u n f o r t u n a t e l y these e f f o r t s have met w i t h l i m i t e d s u c c e s s ( 6 - 8 ) . One o f the b e t t e r s t a b i l i z e r s , a - m e t h y l s t y rene was r e p o r t e d t o be e f f e c t i v e but f o r o n l y 3 months ( 6 ) . Because o f l o n g term r e q u i r e m e n t s , we became concerned w i t h the r e l i a b i l i t y o f these foam systems. In t h i s work t h r e e d i f f e r e n t p o l y u r e t h a n e foam f o r m u l a t i o n s were i n v e s t i g a t e d . The f i r s t was a deployed foam system i n which a c o r r o s i o n s t u d y was performed. Due t o i n c o m p a t i b i l i t i e s , a second and a t h i r d system had t o be f o r m u l a t e d and a g i n g s t u d i e s performed t o i n s u r e a foam system t h a t p r o v i d e d adequate a g i n g c h a r a c t e r i s t i c s . To determine the l a t t e r two s y s t e m s l o n g e v i t y , we s t a r t e d an a c c e l e r a t e d a g i n g program t o s i m u l a t e the i n d i v i d u a l foam component l i f e t i m e s . S p e c i f i c a l l y , the amine e q u i v a l e n t i n the i s o c y a n a t e component and h y d r o x y l e q u i v a l e n t and a c i d number i n the p o l y o l component were f o l l o w e d a t v a r i o u s temperatures (ambient, 60°, 71°C). L i f e t i m e e s t i m a t e s were made by A r r h e n i u s modeling o f the d a t a . The f o l l o w i n g r e s u l t s and d i s c u s s i o n d e s c r i b e the e f f o r t s made t o e v a l u a t e t h e a g i n g c h a r a c t e r i s t i c s o f these foam systems. 1

Experimental The f o r m u l a t e d i s o c y a n a t e and p o l y o l components s u p p l i e d by a vendor ( C o p l a n a r Corp.) were aged i n one g a l l o n s t e e l v e s s e l s . The v e s s e l s were r a t e d a t 250 p s i and equipped w i t h J e n k i n s b a l l v a l v e s and p r e s s u r e r e l i e f diaphragms ( s e t f o r 170 p s i ) . The vapor p r e s s u r e o f F r e o n 11 a t the h i g h e s t a g i n g temperature (71°C) was 60 p s i g g i v i n g a 4/1 s a f e t y margin. The a c t u a l i s o t h e r m a l a g i n g was c a r r i e d out a t ambient, 60° and 71°C. A n a l y s i s o f the i s o c y a n a t e was a c c o m p l i s h e d by p e r f o r m i n g an amine e q u i v a l e n t d e t e r m i n a t i o n ( p e r ASTM D1638). The p o l y o l component was a n a l y z e d f o r h y d r o x o l e q u i v a l e n t by an a c e t y l a t i o n p r o c e dure developed a t Sandia N a t i o n a l L a b o r a t o r i e s . An 0.8 gram sample i s a c e t y l a t e d w i t h a 1/9 a c e t i c a n h y d r i d e - p y r i d i n e m i x t u r e f o r 2 hours a t r e f l u x temperature and then the f r e e a c e t i c a c i d i s back t i t r a t e d w i t h base and compared t o a b l a n k . From t h i s i n f o r m a t i o n a h y d r o x o l e q u i v a l e n t can be c a l c u l a t e d . The p o l y o l a c i d number was d e t e r m i n e d by ASTM D2849. Background - C o r r o s i o n Study o f F o r m u l a t i o n 1 A two component p o l y u r e t h a n e f o r m u l a t i o n was s t o r e d i n the f i e l d i n s e p a r a t e 208 l i t e r (55 g a l ) v e s s e l s o f 0.95 cm w a l l t h i c k n e s s and under a 0.35 t o 0.9 MN/m (50-100 p s i ) over p r e s s u r e . Upon demand the components a r e mixed and d i s c h a r g e d t o form a r i g i d foam; r e 2



30.

WISCHMANN

Polyurethane Foam Component Lifetimes

343

q u i r e m e n t s n e c e s s i t a t e a foam d e n s i t y of 0.016 t o 0.032 g/cc (1-2 l b / f t ^ ) and 1-3 minute t a c k time. The p o l y o l component c o n s i s t s o f a p o l y p r o p y l e n e o x i d e adduct o f p h o s p h o r i c a c i d . Upon a g i n g i n the p r e s e n c e o f m o i s t u r e , t h i s phosphate e s t e r can h y d r o l y z e to phosp h o r i c a c i d which c o u l d l e a d t o c o r r o s i o n o f the m e t a l c o n t a i n e r as w e l l as change the r e s u l t a n t foaming c h a r a c t e r i s t i c s . To d e t e r m i n e whether a p o t e n t i a l l y hazardous c o n d i t i o n p r e v a i l e d a c o r r o s i o n s t u d y was conducted* The p o l y o l component was known t o c o n t a i n 26.8% by weight of the phosphate e s t e r . From a known h y d r o x y l number, a m o l e c u l a r weight of a p p r o x i m a t e l y 382 was c a l c u l a t e d . Assuming complete h y d r o l y s i s , about 7% by w e i g h t o f p h o s p h o r i c a c i d would be formed. A c t u a l l y comp l e t e h y d r o l y s i s i s u n l i k e l y , however, a worst case s i t u a t i o n was d e s i r e d f o r t h i s a c c e l e r a t e d s t u d y . There are two commonly used methods to d e t e r m i n e c o r r o s i o n r a t e s : 1) a w e i g h t l o s s t e c h n i q u e and 2) T a f e l e x t r a p o l a t i o n ( e l e c t r o c h e m i c a l method). A w e i g h t l o s s exp e r i m e n t was performed i n : 1) 7% p h o s p h o r i c a c i d i n water ( d i s s o c i a t e d ) , a g a i n a w o r s t case s i t u a t i o n and 2) w i t h c o n c e n t r a t e d a c i d ( e s s e n t i a l l y u n d i s s o c i a t e d ) as i t might appear i n an o r g a n i c medium. The i n i t i a l r a t e o f 0.188 and 0.043 mm/year i n 7% and concentrated p h o s p h o r i c a c i d r e s p e c t i v e l y d e c r e a s e d w i t h time, most l i k e l y due to c o r r o s i o n p r o d u c t b u i l d u p and i n s o l u b i l i t y i n c o n c e n t r a t e d a c i d . A v a l u e o f a p p r o x i m a t e l y 0.102 mm/year appears to be a r e a s o n a b l e e s t i mate f o r l o n g term exposure i n the 7% a c i d and about 0.003 mm/year f o r the c o n c e n t r a t e d p h o s p h o r i c a c i d . From t h i s d a t a i t was c o n c l u d ed t h a t the t e s t e d s t e e l shows b e t t e r r e s i s t a n c e i n c o n c e n t r a t e d r a t h e r than 7% p h o s p h o r i c a c i d . The i n i t i a l c o r r o s i o n r a t e f o r m i l d s t e e l i n 7% a c i d (pH=l) was v e r i f i e d by the T a f e l e x t r a p o l a t i o n method. R e s u l t s i n d i c a t e an i n i t i a l r a t e o f 0.18 mm/year which was i n c l o s e agreement t o the v a l u e d e t e r m i n e d by the weight l o s s method. The above r e s u l t s must be tempered w i t h the f o l l o w i n g c o n s i d e r a t i o n s t h a t were o m i t t e d from t h i s s t u d y : 1) the v e s s e l was under a c o n s t a n t p r e s s u r e o f 0.35 t o 0.7 MN/m^ (50-100 p s i ) and may r e a c h 2.0 MN/m^ (300 p s i ) when the m a t e r i a l i s d i s p e n s e d , t h i s would a f f e c t the c o r r o s i o n r a t e ; 2) the t e s t i s v e r y s e n s i t i v e t o e n v i r o n m e n t a l changes, e.g., t e m p e r a t u r e , s o l u t i o n homogeneity; 3) the t e s t s were not conducted on a c t u a l c o n t a i n e r m a t e r i a l s , d a t a i n the l i t e r a t u r e show t h a t some s t e e l s c o r r o d e a t a much h i g h e r r a t e i n p h o s p h o r i c a c i d ; and 4) t h e r e may be s u r f a c e d e f e c t s i n the v e s s e l t h a t c o u l d l e a d t o a c c e l e r a t e d l o c a l a t t a c k and premature f a i l u r e . W i t h t h e s e q u a l i f i c a t i o n s , assuming complete h y d r o l y s i s (which i s u n l i k e l y ) and i n c o m p l e t e d i s a s s o c i a t i o n , e x c e s s i v e c o r r o s i o n would not be e x p e c t e d . However, t h e s e c h e m i c a l changes w i l l a f f e c t the foaming c h a r a c t e r i s t i c s , t h e r e b y y i e l d i n g a p r o d u c t t h a t does not meet d e s i g n s p e c i f i cations. S i n c e the phosphate e s t e r ' s o n l y purpose was f i r e r e t a r d a t i o n , a new nonphosphate system was recommended f o r f u t u r e a p p l i c a t i o n s . The f o l l o w i n g d i s c u s s i o n a d d r e s s e s the r e s u l t s o f an a c c e l e r a t e d a g i n g s t u d y on t h i s f o r m u l a t i o n . Discussion - Accelerated

A g i n g Study o f F o r m u l a t i o n

2

A second new d i s p e n s a b l e r i g i d p o l y u r e t h a n e foam f o r m u l a t i o n was a c q u i r e d t h a t d i d not c o n t a i n the phosphate a d d u c t s . C r i t i c a l d e s i g n r e q u i r e m e n t s were the same as i n the f i r s t f o r m u l a t i o n . The r e s p e c -


344


t i v e i s o c y a n a t e and p o l y o l components were p l a c e d i n ovens f o r i s o t h e r m a l a g i n g . We have p r e v i o u s l y found t h a t about a 10% change i n amine and h y d r o x y l e q u i v a l e n t s would a l t e r foaming, e.g., t a c k t i m e , s u f f i c i e n t l y t o d e v i a t e from d e s i g n r e q u i r e m e n t s . Thus, l i f e t i m e e s t i m a t e s a r e based on a 10% change i n the above a n a l y t i c a l parameters. A f t e r 180 days a g i n g , the i s o c y a n a t e aged a t a slow c o n t r o l l e d r a t e (see F i g u r e 1) whereas the p o l y o l showed a d r a m a t i c change a t 7l°C and 180 days a g i n g (see Table I ) . B e f o r e d i s c u s s i n g the reasons f o r the p o l y o l s u n u s u a l b e h a v i o r a d e s c r i p t i o n o f the i s o c y a n a t e a g i n g w i l l f o l l o w . F i r s t , i t was b e l i e v e d t h a t component A would show the most pronounced e f f e c t s o f a g i n g , s i n c e i s o c y a n a t e s a r e p a r t i c u l a r l y s u s c e p t i b l e t o m o i s t u r e a t t a c k . I n a 14 month s t u d y , r e a c t i o n w i t h the water was assumed t o be the p r i m a r y a g i n g r e a c t i o n determining isocyanate l i f e t i m e . I f one uses the amine e q u i v a l e n t a s a damage parameter, an A r r h e n i u s p l o t can be c o n s t r u c t e d (see F i g u r e 2). From t h i s d a t a an a c t i v a t i o n energy (fiJL) o f ^9.3 k c a l / m o l e was c a l c u l a t e d . ThisΔΕ corresponds q u i t e n i c e l y w i t h l i t e r a t u r e values (9) f o r o t h e r s i m i l a r i s o c y a n a t e r e a c t i o n s w i t h water. Employing the A r r h e n i u s p l o t , l i f e t i m e e s t i m a t e s can be made w i t h v a r i o u s a g i n g temperatures. For example, i f the i s o c y a n a t e component A was aged c o n t i n u o u s l y a t 23°C, i t would take 6-8 y e a r s f o r a 10% change i n amine e q u i v a l e n t t o take p l a c e . I f aged a t 49°C (120°F), i t would t a k e o n l y 2 y e a r s f o r the same amount o f a g i n g (see F i g u r e 3 ) . Based on these p r o j e c t i o n s , a m a t e r i a l change-out would be recommended i n 6-7 y e a r s .


1

Table I.

Foam Long-Term S t a b i l i t y f o r F o r m u l a t i o n I I Chemical A n a l y s i s

0 Component A ( I s o c y a n a t e ) Amine E q u i v a l e n t , Ambient Amine E q u i v a l e n t , 60°C Amine E q u i v a l e n t , 71°C Component Β ( P o l y o l ) H y d r o x y l E q u i v a l e n t , Ambient H y d r o x y l E q u i v a l e n t , 60°C H y d r o x y l E q u i v a l e n t , 71°C A c i d Number, Ambient A c i d Number, 60°C A c i d Number, 71°C

30 days

90 days

180 days

142

142 142 144

142 144 147

142 145 150

104

105 107 107

104 104 107

106 108 191

0.2

0.8 2.0 2^0

0.6 1.5 3.0

1.0 2.0 111.0

The p o l y o l component Β e x p e r i e n c e d c a t a s t r o p h i c change i n both h y d r o x o l e q u i v a l e n t and a c i d number a t 71°C and 180 days a g i n g . Be cause o f the l a r g e i n c r e a s e i n a c i d number, i t was i n i t i a l l y thought t h a t Freon 11 ( t r i c h l o r o f l u o r o m e t h a n e ) was g e n e r a t i n g f r e e h y d r o c h l o r i c a c i d by r e a c t i o n w i t h o t h e r components. Free h y d r o c h l o r i c a c i d was v e r i f i e d by a d d i n g AgN03 t o an aged p o l y o l sample and o b t a i n i n g a p r e c i p i t a t e o f A g C l . The l i t e r a t u r e c e r t a i n l y c o n f i r m s t h e i n s t a b i l i t y o f Freon 11 ( 1 ) , t h e r e f o r e a s u p e r i o r s t a b i l i z e r was




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sought. Communication w i t h the m a n u f a c t u r e r , r e v e a l e d t h a t the s t a b i l i z e r used i n Freon 11 was a m a t e r i a l c a l l e d a l l o o c i m e n e ( 2 , 6 - d i m e t h y l 2 , 4 , 6 - o c t a t r i e n e ) . The m a n u f a c t u r e r suggested employ i n g 1% by weight α-methylstyrene as a s t a b i l i z e r . The p o l y o l a g i n g s t u d y was r e p e a t e d u s i n g the newly s t a b i l i z e d t r i c h l o r o f l u o r o m e t h a n e , termed Freon 11A. At e x a c t l y the same a g i n g s t a t i o n (180 d a y s ) , a g a i n l a r g e changes i n h y d r o x y l e q u i v a l e n t and a c i d number o c c u r r e d . CC1 F + CH CH 0H Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 25, 2016 | http://pubs.acs.org Publication Date: October 14, 1986 | doi: 10.1021/bk-1986-0322.ch030

3

3

2

•

CHC1 F + CH3CHO + 2

HC1

Why the r e a c t i o n t a k e s p l a c e so d r a m a t i c a l l y a t about 180 days r a t h e r t h a n g r a d u a l l y i s not u n d e r s t o o d ; perhaps i t i s s i m p l y due t o an i n d u c t i o n p e r i o d o r perhaps the s t a b i l i z e r i s expended a t t h a t time. T h i s r e a c t i o n i s not a w i d e l y known t e x t book r e a c t i o n , i n f a c t , i t was o n l y found i n the p a t e n t l i t e r a t u r e ( 4 ) . However, t h i s r e a c t i o n e x p l a i n s the evidence o f f r e e h y d r o c h l o r i c a c i d . S i n c e a c a r b o n y l group, e.g., aldehyde, was generated by the above r e a c t i o n , t h i s group s h o u l d be o b s e r v a b l e i n the IR. Subsequent IR scans o f the aged p o l y o l r e v e a l e d f o r m a t i o n o f a c a r b o n y l a t about 5.8 microns. Unaged p o l y o l shows n e g l i g i b l e c a r b o n y l f o r m a t i o n . A c c o r d i n g t o the p a t e n t ( 4 ) , t h i s r e a c t i o n i s p e c u l i a r t o any c h l o r o f l u o r o a l k a n e c o n t a i n i n g t h r e e o r more c h l o r i n e s , i . e . , t r i c h l o r o t r i f l u o r o e t h a n e s , C2F3CI3; t e t r a c h l o r o d i f l u o r o e t h a n e s , C2F3CI4. D i c h l o r o f l u o r o a l k a n e s , i . e . , Freon 12, d i c h l o r o d i f l u o r o methane, are a p p a r e n t l y f r e e from such r e a c t i o n s . The r e a c t i o n o f F r e o n 11 w i t h a p o l y o l appears i n e s c a p a b l e ; c o n s e q u e n t l y l o n g term s t o r a g e o f foam systems of t h i s c o m p o s i t i o n a r e not a d v i s a b l e . Formulation

3

At t h i s j u n c t u r e , i t was d e c i d e d t o make a r a d i c a l f o r m u l a t i o n change. F i r s t , because o f the i n c o m p a t i b i l i t y o f the Freon 11 w i t h the p o l y o l , the F r e o n 11 would be removed from the p o l y o l and p l a c e d i n the i s o c y a n a t e component. Second, s i n c e 1/1 component r a t i o s a r e n e c e s s a r y t o accommodate the m i x i n g machine, d i f f e r e n t i s o c y a n a t e and p o l y o l components were f o r m u l a t e d t o e s t a b l i s h a p p r o p r i a t e v i s c o s i ties. The f i n a l f o r m u l a t i o n i s shown below. Isocyanate PAPI-580 F r e o n 11

Component A

P o l y o l Component Β

117 pbw 33 pbw

PEP-550 DC-197 DABCO F r e o n 12

117 1 5 25

pbw pbw pbw pbw

I n subsequent a g i n g s t u d i e s the p o l y o l component showed v i r t u a l l y no change i n a c i d number a t any of the a g i n g t e m p e r a t u r e s (ambi e n t , 60°, 71°C) over 13 months. The i s o c y a n a t e was shown t o age s i m i l a r l y t o the i s o c y a n a t e i n F o r m u l a t i o n 2. As a r e s u l t , the above f o r m u l a t i o n i s b e i n g employed i n the f i e l d . Summary And Two

Conclusions

d i f f e r e n t dispensable r i g i d polyurethane

found inadequate

foam f o r m u l a t i o n s were

o v e ^ ^ P ^ g f o f ^ f i ^ j g ^ e f i r s t system c o n Library

1155 16th St., N.W. Dickie and Floyd; Polymeric Materials for Corrosion Control Washington, D.C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


348

POLYMERIC MATERIALS FOR CORROSION C O N T R O L

t a i n e d p h o s p h o r i c a c i d a d d u c t s which can h y d r o l y z e i n the p r e s e n c e o f m o i s t u r e , t h e r e b y c h a n g i n g t h e i r foaming c h a r a c t e r i s t i c s . A refor m u l a t e d system e x c l u d i n g t h e phosphate e s t e r s a l s o e x h i b i t e d poor a g i n g , s i m p l y because the Freon 11 b l o w i n g agent r e a c t s w i t h the p o l y o l l i b e r a t i n g f r e e h y d r o c h l o r i c a c i d , an unacceptable s i t u a t i o n . The l a t t e r r e a c t i o n was not common knowledge, y e t , i t must be r e c o g n i z e d i n v i e w o f t h e w i d e - s p r e a d p o p u l a r i t y o f t h i s r e f r i g e r a n t and b l o w i n g agent* F i n a l l y , a t h i r d f o r m u l a t i o n was d e v i s e d w h i c h e x c l u d e d t h e use o f F r e o n 11 i n t h e p o l y o l component. F r e o n 11 was p l a c e d i n t h e i s o c y a n a t e component and b o t h i s o c y a n a t e and p o l y o l components were changed t o meet v i s c o s i t y c o n s i d e r a t i o n s * Subsequent a g i n g s t u d i e s showed the i s o c y a n a t e t o age s i m i l a r l y t o the p r e v i o u s l y aged ( F o r m u l a t i o n 2) i s o c y a n a t e . The p o l y o l showed v i r t u a l l y no i n c r e a s e i n a c i d number a t any a g i n g temperature o v e r 13 months. Thus, a t ambient t e m p e r a t u r e we would e x p e c t a 6-8 y e a r system l i f e t i m e on the i s o c y a n a t e b e f o r e a 10% change i n a n a l y t i c a l p r o p e r t i e s would d i c t a t e a m a t e r i a l change-out. The p o l y o l appears t o have a g r e a t e r l i f e t i m e , but would p r o b a b l y be r e p l a c e d a t the same t i m e . Acknowledgments The a u t h o r g r a t e f u l l y acknowledges S. L. Pohlman f o r c o n d u c t i n g t h e c o r r o s i o n s t u d y , S. L. E r i c k s o n f o r t h e a n a l y t i c a l d a t a , and C. A r n o l d f o r h e l p f u l d i s c u s s i o n s . Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9.

Church, J . M . ; Mayer, J . H. J . Chem. Eng. 1961, 6, 449. Parmelee, H. M . : Downing, R. C. Soap S a n i t . Chem. 1950, 26, 114. Parmelee, H. M . ; Downing, R. C. Pro. Chem. S p e c i a l t i e s Manu facturers Assoc. 1950, 45, 47. Bauer, A. W. U . S . Patent 3 183 192, 1965. Eiseman, B. J. Progr. R e f r i g . S c i . Technol. 1973, 2, 643. Degginer, E . R . ; Knapp, W. Α.; Zuem, Η. E . U.S. Patent 3 352 789. Blodgett, F . W. U.S. Patent 3 361 833. DuPont, Belgium Patent 621 364. Wright, P; Cumming, A. P. C. " S o l i d Polyurethane Elastomers"; McClearen and Sons, 1969.

R E C E I V E D January 22, 1986


Polymeric Materials for Corrosion Control - American Chemical Society

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