5 A Low Molecular Weight Esterified Copolymer of Styrene and Maleic Anhydride
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For Electrodeposition J O H N F. M O T I E R and D O N A L D L . M A R I O N A R C O Chemical Co., Division of the Atlantic Richfield Co., Philadelphia, Pa. 19145
A partially esterified low molecular weight copolymer of styrene and maleic anhydride has demonstrated exceptional properties as an electrodeposition vehicle. When crosslinked with an amino resin and cured at 360°F copolymer
yielded
electrodeposited
for 25 minutes, the films
(unpigmented)
possessing salt spray resistance in excess of 450 hours. Varia tions in curing cycle had little effect on corrosion resistance. Throwing 7-8 1/2
power (steel pipe method) was in the range of inches, and the coated throwing power strips ex
hibited excellent corrosion resistance. By employing a bak ing temperature of 450°F, films resisted attack by detergent (1% Tide XK solution at 165°F)
for 175 hours.
Coulombic
yield of the resin system was ca. 46 mg per coulomb. Infra red spectroscopy revealed that the low molecular weight styrene-maleic
anhydride copolymer and the amino cross-
linking agent migrate to the anode at comparable rates.
T n the e l e c t r o c o a t i n g field m a n y resin systems h a v e a c h i e v e d t e c h n i c a l -*· a n d c o m m e r c i a l success as coatings f o r e l e c t r i c a l l y c o n d u c t i v e sub strates.
F o r a c o m p i l a t i o n o f these, together w i t h a b i b l i o g r a p h y p r o
v i d i n g a n extensive r e v i e w of electrocoating, the m o n o g r a p h s b y C h a n d ler should be consulted
(1-3).
I n this l a b o r a t o r y recent
w o r k has
d e m o n s t r a t e d t h e u t i l i t y of a p a r t i a l l y esterified l o w m o l e c u l a r w e i g h t c o p o l y m e r of styrene a n d m a l e i c a n h y d r i d e ( S M A - I ) as a n e l e c t r o c o a t i n g v e h i c l e w h i c h y i e l d s films e x h i b i t i n g excellent c o r r o s i o n a n d detergent resistance.
A t t e n t i o n was c e n t e r e d o n this t y p e of r e s i n because p r e v i o u s
w o r k (4)
d e m o n s t r a t e d these characteristics w i t h solvent-based b a k i n g 80
Brewer; Electrodeposition of Coatings Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
5.
MOTiER
enamels
81
Sty rene-M oleic Anhydride
A N D MARION
d e r i v e d f r o m a s i m i l a r resin.
[These copolymers
a n d their
p a r t i a l esters are a v a i l a b l e f r o m A R C O C h e m i c a l C o . u n d e r t h e trade name S M A . ] T h e synthesis of this t y p e o f p o l y m e r is o u t l i n e d i n F i g u r e 1 ( 5 ) a n d is b a s e d o n free r a d i c a l c h a i n p o l y m e r i z a t i o n f o l l o w e d b y esterification.
A s a result of the p o l y m e r i z a t i o n process the resins are a v a i l a b l e
as solids. A b r o a d r a n g e of r e s i n properties is m a d e p o s s i b l e b y v a r y i n g the ratio o f the m o n o m e r s p o l y m e r i z e d as w e l l as the c h e m i c a l c o m p o s i t i o n of t h e e s t e r i f y i n g a l c o h o l ( s )
a n d the extent of esterification.
Thus
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the b a l a n c e of styrene a n d m a l e i c a n h y d r i d e units i n c o n j u n c t i o n w i t h the e s t e r i f y i n g a l c o h o l ( s ) establishes the c a r b o x y l f u n c t i o n a l i t y a v a i l a b l e f o r r e a c t i o n w i t h c r o s s l i n k i n g resins.
CH=CH
CH = CH
?
+nl
CH-
I Catalyst
CH-
I
0
0
OJ
ROH
^CH -CH^
\
/m
/
ÇH—(pH ι
2
dVS>
\
l-x
CH—CH
\o o v
\ H X
