(Hydroxyalkyl)acrylamide Copolymers for Corrosion Control

25

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N-(Hydroxyalkyl)acrylamide Copolymers for Corrosion Control F. Chen Betz Laboratories, Inc., Somerton Road, Trevose, PA 19047

The study was an attempt to c o r r e l a t e polymer s t r u c t u r e to i t s a c t i v i t y i n water treatment applications. Copolymers of a c r y l i c acid with N-(hydroxymethyl)-, N - ( 2 - h y d r o x y e t h y l ) - , and N-(2-hydroxypropyl) acrylamide were prepared. The r e s u l t i n g a c r y l i c a c i d / N - ( h y d r o x y a l k y 1 ) acrylamide copolymers were evaluated for t h e i r deposit c o n t r o l and d i s p e r s a n t a c t i v i t i e s as compared to the homopolymer of a c r y l i c a c i d . Differences i n the activities could be a t t r i b u t e d to the i n c o r p o r a t i o n of the N - h y d r o x y l a l k y l a c r y l a m i d e moiety i n t o the polymer c h a i n . C o r r o s i o n i s t h e d e s t r u c t i o n o f a m e t a l by c h e m i c a l or e l e c t r o c h e m i c a l r e a c t i o n with i t s environment. To i n c r e a s e e q u i p m e n t r e l i a b i l i t y a n d p l a n t efficiency, c o r r o s i o n i n h i b i t o r s a r e used i n b o i l e r and c o o l i n g water programs t o c o n t r o l f o u l i n g andd e p o s i t i o n on c r i t i c a l heat-transfer surfaces. Incooling systems, c o r r o s i o n i n h i b i t i o n i s commonly a c h i e v e d t h r o u g h t h e use o f p a s s i v a t o r s , w h i c h e n c o u r a g e t h e f o r m a t i o n o f a p r o t e c t i v e m e t a l o x i d e f i l m on t h e m e t a l s u r f a c e O ) · A l t h o u g h chromate i s t h e best aqueous c o r r o s i o n i n h i b i t o r a v a i l a b l e , i t s use has been s e v e r e l y curtailed due t o t o x i c i t y a n d e n v i r o n m e n t a l c o n c e r n s · One o f t h e more s u c c e s s f u l n o n - c h r o m a t e t r e a t m e n t s i n v o l v e s t h e use o f p h o s p h a t e / p h o s p h o n a t e c o m b i n a t i o n s . This treatment employs high l e v e l s o f orthophosphate t o promote p a s s i v a t i o n o f t h e metal s u r f a c e s . Therefore, i t i s important tocontrol calcium phosphate c r y s t a l l i z a t i o n so t h a t high l e v e l s o f o r t h o p h o s p h a t e may b e m a i n t a i n e d i n t h e s y s t e m w i t h o u t f o u l i n g o r impeding h e a t - t r a n s f e r functions. Low-molecular-weight carboxyl-containing polymers have been used t o c o n t r o l t h e d e p o s i t i o n o f c a l c i u m phosphate (2-8). These p o l y m e r s a l s o f u n c t i o n as 0097-6156/86/0322-0283S06.00/ 0 © 1986 American Chemical Society

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

POLYMERIC MATERIALS FOR CORROSION CONTROL

284

d i s p e r s a n t s t o reduce t h e f o r m a t i o n o f s c a l e from calcium carbonate, calcium sulfate, iron oxide, clay, etc. Other a c r y l a m i d e - b a s e d c o p o l y m e r s , such as d i c a r b o x y m e t h y l a c r y l a m i d e (JO a n d a l k y l o l a m i d e , h a v e been r e p o r t e d b u t a r e n o t y e t c o m m e r c i a l l y significant (10-11). Copolymers o f a c r y l i c a c i d w i t h Jtf-(hydroxymethyl)-, N - ( 2 - h y d r o x y e t h y l ) - , and N - ( 2 - h y d r o x y p r o p y l ) a c r y l a m i d e w e r e p r e p a r e d i n m o l e r a t i o s o f 3:1 [ a c r y l i c a c i d / N - ( h y d r o x y a l k y l ) - a c r y l a m i d e ] and s i m i l a r m o l e c u l a r weights i n order to study the e f f e c t that the v a r i a t i o n s i n p o l y m e r s t r u c t u r e have on a c t i v i t y . The r e s u l t i n g c o p o l y m e r s were t h e n e v a l u a t e d f o r t h e i r d e p o s i t c o n t r o l a c t i v i t y by c o m p a r i n g them t o t h e h o m o p o l y m e r o f a c r y l i c a c i d ( a l s o i n a s i m i l a r m o l e c u l a r weight range). Thus, t h e d i f f e r e n c e i n a c t i v i t y may be a t t r i b u t e d t o t h e p a r t i c u l a r f u n c t i o n a l group of the N - ( h y d r o x y a l k y l ) acrylamide moiety. Experimental

Section

M a t e r i a l s : C o m m e r c i a l g r a d e a c r y l i c a c i d (Rohm a n d Haas) and N - ( h y d r o x y m e t h y l ) a c r y l a m i d e (N-methylol a c r y l a m i d e , A m e r i c a n Cyanamid) were used w i t h o u t purification. A c e t o n i t r i l e was d r i e d o v e r m o l e c u l a r s i e v e s ( 4 A ) and d i s t i l l e d p r i o r t o u s e . Ethanolamine and l - a m i n o - 2 - p r o p a n o l were vacuum d i s t i l l e d . Reagent g r a d e a c r y l o y l c h l o r i d e , 2 - p r o p a n o l , and sodium p e r s u l f a t e were used as r e c e i v e d . Monomer S y n t h e s i s : N - ( 2 - h y d r o x y e t h y l ) - and N - ( 2 - h y d r o x y p r o p y l ) a c r y l a m i d e were p r e p a r e d from t h e r e a c t i o n o f a c r y l o y l c h l o r i d e w i t h e t h a n o l a m i n e and l-amino-2-propanol, r e s p e c t i v e l y , i n a c e t o n i t r i l e : CH =CHC0C1 2

+ 2NH CH CH OH 2

2

>

2

C H = CHCONHCH CH OH 2

CH -CHC0C1 2

2

+ 2NH CH CH(OH)CH 2

2

CH =CHCONHCH CH(OH)CH 2

2

2

3

3

+ HC1 . N H ^ H ^ H ^ H

i

>

+ HC1.NH CH CH(OH)CH 2

2

3

|

1- A m i n o - 2 - p r o p a n o l was u s e d i n s t e a d o f 3 - a m i n o - l p r o p a n o l s o t h a t t h e h y d r o x y g r o u p w o u l d be o n t h e 2- p o s i t i o n , a s i n N - ( 2 - h y d r o x y e t h y l ) a c r y l a m i d e . R e a c t i o n s w e r e c a r r i e d o u t a t - 1 5 C i n s t e a d o f -5 t o -10°C a s r e p o r t e d i n t h e l i t e r a t u r e (9_) t o o b t a i n a higher y i e l d . A f t e r t h e r e a c t i o n , t h e m i x t u r e was s t i r r e d o v e r n i g h t and then f i l t e r e d . The f i l t e r e d h y d r o x y a l k y l a m i n e h y d r o c h l o r i d e s a l t was w a s h e d s e v e r a l times with c h i l l e d a c e t o n i t r i l e . The f i l t r a t e s w e r e c o m b i n e d , a n d t h e n t h e a c e t o n i t r i l e was r e m o v e d b y vacuum d i s t i l l a t i o n . Trace amounts o f p-methoxyphenol


25.

CHEN

285

N-(Hydroxyalkyl)acrylamide Copolymers

( 3 0 0 ppm) w e r e a d d e d t o p r e v e n t self-polymerization during the d i s t i l l a t i o n . Structure and p u r i t y o f t h e d i s t i l l e d p r o d u c t s were v e r i f i e d by C NMR a n d I R spectroscopy. Copolymerization: N-(Hydroxymethyl)-, N-(2-hydroxye t h y l ) - , and N - ( 2 - h y d r o x y p r o p y l ) a c r y l a m i d e were c o p o l y m e r i z e d w i t h a c r y l i c a c i d , i n an aqueous medium. S o d i u m p e r s u l f a t e was u s e d a s t h e i n i t i a t o r . Acrylic a c i d was p a r t i a l l y n e u t r a l i z e d ( c a . 80 m o l %) w i t h sodium hydroxide s o l u t i o n . After the n e u t r a l i z a t i o n , t h e r e s p e c t i v e J N - ( h y d r o x y a l k y l ) a c r y l a m i d e was a d d e d t o the s o l u t i o n and s t i r r e d . The monomer a n d i n i t i a t o r s o l u t i o n s were t h e n added t o a r e a c t i o n f l a s k containing w a t e r a n d 2 - p r o p a n o l a t 85 t o 90°C. A d d i t i o n t i m e was approximately 2 hours. After the addition, the reaction m i x t u r e was h e a t e d f o r a n a d d i t i o n a l h o u r a n d , s u b s e q u e n t l y , a s p e c i f i c a m o u n t o f 2 - p r o p a n o l / w a t e r was stripped off. The r e s u l t i n g p o l y m e r s o l u t i o n was c o o l e d and f i l t e r e d . The f i l t r a t e was c l e a r a n d s t a b l e a t r o o m temperature. The d e t a i l e d p r o p e r t i e s o f t h e r e s p e c t i v e p o l y m e r s o l u t i o n s a r e s h o w n i n T a b l e I . As a n a l y z e d b y C NMR, t h e c o m p o s i t i o n ( m o l r a t i o ) o f t h e r e s u l t i n g c o p o l y m e r s was a l s o c l o s e t o t h a t o f 3 : 1 . T h i s could i n d i c a t e that under the r e a c t i o n c o n d i t i o n s used t h e

Table Sample No.

Comp—

I:

MolarRatio

PA

-

, £ -

Physical

Properties

Brookfield— V i s e .cps,25°C

Mol pH

200-500 (50.0% s o l i d s )

-

WtMn_ 2,100

AA/HMAMD

3: 1

20.3 5.9 (22.3% s o l i d s )

3,600

AA/HEAMD

3:1

18.9 5.6 (24.7% s o l i d s )

2,900

AA/HEAMD

3:1

18.0 (23.6% s o l i d s )

5.9

2,340

AA/HPAMD

3:1

16.0 (24.1% s o l i d s )

5.9

2,400

A b b r e v i a t i o n s used: PA, p o l y a c r y l i c a c i d ; AA, a c r y l i c a c i d ; HMAMD, N - ( h y d r o x y m e t h y l ) a c r y l a m i d e ; HEAMD, N - ( 2 h y d r o x y e t h y l ) a c r y l a m i d e ; HPAMD, N - ( 2 - h y d r o x y p r o p y l ) acrylamide. R a t i o o f t h e two monomers c h a r g e d t o r e a c t i o n . U s i n g L V T No. 1 s p i n d l e , 60 r p m . GPC i n 0.05 M Na SO^ s o l u t i o n .


286


h y d r o l y s i s o r d e g r a d a t i o n of t h eN - ( h y d r o x y a l k y l ) a c r y l a m i d e was n o t s i g n i f i c a n t o r t h a t t h e c o p o l y m e r i z a t i o n was a p p r o x i m a t e l y r a n d o m . Results

and D i s c u s s i o n

Evaluation of the Copolymers: The p o l y m e r s o l u t i o n s were e v a l u a t e d f o r t h e i r d e p o s i t c o n t r o l and d i s p e r s a n t activities. The t e s t s i n c l u d e d c a l c i u m p h o s p h a t e i n h i b i t i o n , calcium carbonate i n h i b i t i o n , iron oxide d i s p e r s i o n , and c l a y d i s p e r s i o n . The p r o c e d u r e s f o r t h e s e t e s t s h a v e b e e n p r e v i o u s l y r e p o r t e d (JJO . A c o m m e r c i a l l y a v a i l a b l e p o l y a c r y l i c a c i d was a l s o t e s t e d for comparison. The r e s u l t s a r e s h o w n i n T a b l e s I I t o V. Calcium Phosphate I n h i b i t i o n : Control of soluble phosphates i s important to the success of phosphate/phosphonate treatment programs. The t e s t procedure i n c l u d e d m i x i n g c a l c i u m c h l o r i d e and sodium orthophosphate solutions, allowing the resulting solution to e q u i l i b r a t e for s p e c i f i e d time, f i l t e r i n g the m i x t u r e , and m e a s u r i n g r e s i d u a l , s o l u b l e phosphate ion c o n c e n t r a t i o n . High s o l u b l e phosphate c o n c e n t r a t i o n s i n d i c a t e good d e p o s i t c o n t r o l , s i n c e t h e treatment i n h i b i t e d calcium phosphate c r y s t a l l i z a t i o n . The p e r c e n t i n h i b i t i o n was c a l c u l a t e d a c c o r d i n g t o t h e e q u a t i o n i n T a b l e I I . As s h o w n i n T a b l e I I , t h e r e s u l t s i n d i c a t e d t h a t when c o m p a r e d t o t h e p o l y a c r y l i c a c i d , c o p o l y m e r s o f a c r y l i c a c i d and N - ( h y d r o x y a l k y l ) a c r y l a m i d e were q u i t e e f f e c t i v e i n i n h i b i t i n g c a l c i u m p h o s p h a t e f o r m a t i o n a t t h e n o r m a l u s e d o s a g e o f 10 t o 20 ppm. Among t h e t h r e e c o p o l y m e r s tested, acrylic acid/ N - ( 2 - h y d r o x y e t h y l ) a c r y l a m i d e a p p e a r e d t o be t h e m o s t e f f e c t ive· Calcium Carbonate I n h i b i t i o n : The t e s t procedure i n c l u d e d m i x i n g c a l c i u m c h l o r i d e s o l u t i o n ( w i t h and w i t h o u t t r e a t m e n t ) and c a l c i u m c a r b o n a t e solution. A f t e r e q u i l i b r i u m , f i l t r a t i o n , a n d pH a d j u s t m e n t , t h e r e s i d u a l c a l c i u m i o n c o n c e n t r a t i o n was t h e n titrated by EDTA s o l u t i o n . A higher r e s i d u a l calcium ion concent r a t i o n i n d i c a t e s b e t t e r i n h i b i t i o n a c t i v i t y and, t h e r e f o r e , more e f f e c t i v e n e s s i n c o n t r o l l i n g c a l c i u m c a r b o n ate d e p o s i t i o n i n the t r e a t e d water. As s h o w n i n T a b l e I I I , a t d o s a g e s o f 1 t o 5 ppm, t h e p o l y a c r y l i c a c i d was more e f f e c t i v e t h a n t h e a c r y l i c a c i d / N - ( h y d r o x y a l k y l ) acrylamide copolymers. Dispersant A c t i v i t y : T e s t s were c o n d u c t e d utilizing i r o n o x i d e and c l a y s u s p e n s i o n s i n o r d e r t o e s t a b l i s h the e f f i c a c y o f t h e copolymers as d i s p e r s a n t s f o r suspended p a r t i c u l a t e matter. K a o l i n c l a y was u s e d f o r the c l a y d i s p e r s i o n study. According to the procedure, s e p a r a t e 0.1% i r o n o x i d e s and 0.1% c l a y s u s p e n s i o n s i n


25.

Table Testing

II:

Calcium

Phosphate

Inhibition

Conditions 36.76 g of

J

PO,

(treated)-ppm

„ ppm

PO^

Na

'2H

0/L

of

HP0,/L o f

"(stock)-ppm %

PO, jPO^

3-

χ

Inhibition A c t i v e Dosage 1 0 ppm 20

PA AA/ HMAMD AA/HEAMD, S a m p l e

34 47 55

42 59 59

67 56 65

17 28 7.9

38 67 59

42 83 68

See

2

3

f o o t n o t e a and

100

(control)

5 ppm

—

H«0

(control)

Sample—

PA AA/HEAMD, S a m p l e AA/HPAMD

HO

J

3-

Inhib =

CaCl

0.4482 g o f CaCO.

z

ppm

Test

Solutions

T e m p e r a t u r e 70°C pH 7.5 17 h r e q u i l i b r i u m Ca : 250 ppm a s PO ~ : 6 ppm

%

287


CHEN

sample

# i n Table

ppm

I.

d e i o n i z e d w a t e r were p r e p a r e d . The h a r d n e s s o f e a c h s l u r r y was a d j u s t e d t o 200 ppm Ca a s CaC0~> r e s u l t a n t m e d i a were each mixed u n t i l u n i f o r m s u s p e n sions resulted. The pH o f e a c h s u s p e n s i o n was a d j u s t e d t o a b o u t 7.5. In t h i s t e s t , h i g h e r v a l u e s i n the d i f f e r e n c e o f m e a s u r e d t r a n s m i t t a n c e (Δ%τ) indicate b e t t e r d i s p e r s i n g a c t i v i t y as more p a r t i c l e s remain suspended i n the aqueous medium. As s h o w n i n T a b l e s IV a n d V, c o p o l y m e r s w e r e q u i t e e f f e c t i v e i n d i s p e r s i n g i r o n o x i d e and c l a y as c o m p a r e d to p o l y a c r y l i c a c i d . Among t h e p o l y m e r s t e s t e d , a c r y l i c a c i d / N - ( 2 - h y d r o x y e t h y l ) a c r y l a m i d e s e e m e d t o be t h e m o s t e f f e c t ive· a n d

t n e

Mechanism: I t has been s u g g e s t e d t h a t t h e h y d r o x y l f u n c t i o n a l i t y i s important i n the a d s o r p t i o n of a n i o n i c p o l y e l e c t r o l y t e s from water onto metal o x i d e s ( 1 3 - 1 4 ) . The m e c h a n i s m i n v o l v e s h y d r o g e n b o n d i n g o f t h e h y d r o x y groups to n e g a t i v e l y charged s u r f a c e oxide i o n s : M0~

+

n

H0A ~

*

M0~

...

n

H0A "

χ n

where A r e p r e s e n t s an a n i o n o r a n i o n i c p o l y e l e c t r o l y t e , a n d M0~ i s t h e m e t a l o x i d e i o n . Study a l s o showed t h a t p o 1 y c a r b o x y 1 a t e s c o n t a i n i n g h y d r o x y l g r o u p s


288


Table Testing

III:

Calcium

Carbonate

Conditions

Inhibition

Test

Solutions

T e m p e r a t u r e 70°C pH 9.0 5 hr equilibrium Ca 2 4*2 PPm C0 : 7 0 2 ppm

3.25 g o f C a C l

*2H 0/L o f H 0 ?

1

1

2.48 g o f Na CO / L o f

HO

:

3

7 Inhib °

=

m

L

E

D

T

A

t i t r . ( t r e a t e d ) - m L EDTA t i t r . ( c o n t r o l ) mL EDTA t i t r . ( s t o c k ) -mL EDTA t i t r . ( c o n t r o l ) x 100 %

Inhibition A c t i v e Dosage 3 ppm 5 ppm

S a m p l e —a

1 ppm

PA AA/HMAMD AA/HEAMD,

35 2.8 4.6

59 53 51

69 63 58

15 6.1 0.9

29 29 19

71 51 49

PA AA/HEAMD, AA/HPAMD —

Sample

2

Sample

3

See f o o t n o t e Table

Testing

IV:

Iron

Oxide

Tl

Dispersion

Conditions

Temperature pH Ca

a. a n d s a m p l e ? Γη T a b l e

Test

Solutions

25°C

0 . 1 % S o l u t i o n o f Fe 0. i n H 0 2

7.5 3.68 g o f C a C I : 2 0 0 ppm a s C a C 0

* 2 H 6 / 1 0 0 mL o f H 0 2

2

3

Δ

% Transmittance

Δ

= % Τ (control) - % Τ %

(treated)

Transmittance A c t i v e Dosage 10 ppm 20 ppm

Sample—

5 ppm

PA AA/HMAMD AA/HEAMD,

2.0 18 29

11 30 30

19 35 31

5.7 41 26

12 40 43

23 47 45

PA AA/HEAMD, AA/HPAMD —

Sample

2

Sample

3

See f o o t n o t e

a and sample # i n T a b l e IV.



25. CHEN

Table Testing

V:

Clay

Conditions

T e m p e r a t u r e 25°C pH 7.5 Ca : 2 0 0 ppm a s A,

Dispersion

289

(Kaolin)

Test

Solutions 0 . 1 % S o l u t i o n o f H y d r i t e UF i n H O 3.68 g o f C a C l ' 2 H 0 / 1 0 0 mL o f H^O CaC0 3

% Transmit tance J\

= % Τ (control) - % Τ (treated) %

Transmittance A c t i v e Dosage 10 ppm

Sample—

5 ppm

PA AA/HMAMD AA/HEAMD, S a m p l e

22 31 41

28 35 39

31 30 35

36 60 49

43 51 59

55 49 49

PA AA/HEAMD, S a m p l e AA/HPAMD —

2

3

See f o o t n o t e j i and s a m p l e

# Γΐϊ T a b l e

20

ppm

TZ

a d s o r b a t pHs s i g n i f i c a n t l y a b o v e t h e p o i n t o f z e r o charge. A l t h o u g h t h e r e i s no d i r e c t c o r r e l a t i o n b e t w e e n the e x t e n t o f a d s o r p t i o n and a c t i v i t y d i f f e r e n c e s as shown i n t h i s s t u d y , t h e p o s s i b l e c o n t r i b u t i o n f r o m t h e h y d r o x y l g r o u p c a n n o t be o v e r l o o k e d . The c o p o l y m e r s i n t h i s s t u d y w e r e a l l i n a 3:1 m o l e r a t i o o f a c r y l i c a c i d w i t h N-(hydroxyalkyl)acrylamide· D i f f e r e n t mole r a t i o s and o t h e r m o l e c u l a r w e i g h t ranges may h a v e d i f f e r e n t t e s t i n g r e s u l t s . However, by c o n t i n u i n g t h i s k i n d o f s y s t e m a t i c s t u d y , we may be a b l e to u n d e r s t a n d more a b o u t t h e r e l a t i o n s h i p b e t w e e n p o l y m e r s t r u c t u r e and i t s a c t i v i t y i n w a t e r treatment. Hopefully, i t can f a c i l i t a t e i n choosing or s y n t h e s i z i n g a s p e c i f i c polymer f o r the d e s i r e d a p p l i c a t i o n . Conclusion The o b j e c t i v e o f t h i s s t u d y was t o c o r r e l a t e p o l y m e r structure versus i t s a c t i v i t y f o r corrosion control i n water-tre.a tment a p p l i c a t i o n s . Raw m a t e r i a l a n d manufacturing c o s t s were n o t c o n s i d e r e d . A t t h e same active dosages, a c r y l i c acid/N-(hydroxyalkyl)aerylamide (3:1 mole r a t i o ) c o p o l y m e r s showed an o v e r a l l i m p r o v e d p e r f o r m a n c e i n c a l c i u m p h o s p h a t e i n h i b i t i o n and i r o n o x i d e and c l a y d i s p e r s i o n as compared t o t h e p o l y a c r y l i c acid. Among t h e t h r e e c o p o l y m e r s t e s t e d , a c r y l i c a c i d / N - ( 2 - h y d r o x y e t h y l ) a c r y l a m i d e a p p e a r e d t o be t h e most e f f e c t i v e . D i f f e r e n c e s i n a c t i v i t y were a t t r i b u t e d to the a d d i t i o n a l f u n c t i o n a l group i n t h e copolymer v e r s u s the homopolymer.


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290

Acknowledgment s The author g r a t e f u l l y acknowledges the support ofh i s c o l l e a g u e s a t B e t z a n d , i n p a r t i c u l a r , W. R. S n y d e r f o r a c t i v i t y t e s t i n g a n d L. D. C h a d w i c k f o r C NMR spectroscopy· 1 3

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RECEIVED January 21, 1986


(Hydroxyalkyl)acrylamide Copolymers for Corrosion Control

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