Reactive Oligomers - American Chemical Society

10 Chain Extendable Oligomers for High-Solids Coatings J. W. H O L U B K A

Downloaded by AUBURN UNIV on November 15, 2016 | http://pubs.acs.org Publication Date: July 9, 1985 | doi: 10.1021/bk-1985-0282.ch010

Research Staff, Ford Motor Company, Dearborn,MI48121

High solids coating systems usually employ low molecular weight multifunctional adducts or polymers in combination with multifunctional crosslinking agents. The networks that result upon curing differ substantially in structure and morphology from networks generated from conventional coating formulations that incorporate relatively high molecular weight polymers and crosslinkers. This paper describes three reactive oligourethane oligomers that incorporate chemical functionality that allows chain extension to occur during cure. The chain extension occurs preferably as a reaction independent of crosslinking and generates, in situ, during cure, a conventional high molecular weight polymer. One reactive oligomer incorporates blocked isocyanate-polyol chemistry that undergoes chain extension, during cure, to form hydroxy functional polyurethanes that are subsequently crosslinked, in situ, with conventional aminoplast crosslinkers. The remaining two reactive oligomers use blocked isocyanate-epoxy and t-butyl carbamate-epoxy chemistry for chain extension and subsequent self-crosslinking through formation of the corresponding oxazolidone and epoxy-amine linkages respectively. H i g h s o l i d s c o a t i n g systems u s u a l l y employ l o w m o l e c u l a r w e i g h t m u l t i f u n c t i o n a l adducts or copolymers i n combination w i t h m u l t i f u n c t i o n a l c r o s s l i n k i n g agents. T y p i c a l l y , these f o r m u l a t i o n s y i e l d networks t h a t d i f f e r g r e a t l y from those formed i n c o n v e n t i o n a l c o a t i n g systems that i n c o r p o r a t e r e l a t i v e l y high molecular weight hydroxy f u n c t i o n a l polymers. I n t h i s paper, the s y n t h e s i s and chemistry of t h r e e r e a c t i v e urethane o l i g o m e r s t h a t c a n undergo c h a i n e x t e n s i o n during cure are reported. These o l i g o m e r s r e f e r r e d to as urethane m o d i f i e d e p o x y - d i o l o l i g o m e r , Type I u r e a - u r e t h a n e o l i g o m e r and Type II urea-urethane oligomer, are also described i n high s o l i d coating formulations.

0097-6156/85/0282-0117$06.00/0 © 1985 American Chemical Society

Harris and Spinelli; Reactive Oligomers ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

REACTIVE OLIGOMERS

118 Experimental


E p o x y - d l o l Adduct. The e p o x y - d i o l a d d u c t s were p r e p a r e d u s i n g s t a n d a r d t e c h n i q u e s (1_) b y h e a t i n g a m i x t u r e o f two m o l e s o f d i o l w i t h o n e m o l e o f e p o x y r e s i n a t 1 3 0 - 1 4 0 ° C f o r 8 h o u r s u s i n g 1% Ν,Ν-dimethylethanolamine as c a t a l y s t . E p o x y - d i o l adducts prepared i n t h i s manner showed t h e a b s e n c e o f epoxy a b s o r p t i o n i n t h e i n f r a r e d spectrum. Half-blocked Diisocyanates. The h a l f - b l o c k e d d i i s o c y a n a t e s were p r e p a r e d u s i n g c o n v e n t i o n a l methods (2) by a d d i n g d r o p w i s e , o v e r a p e r i o d o f one h o u r , 1 m o l e o f a l c o h o l t o 1 m o l e o f d i i s o c y a n a t e a n d 100 mg d i b u t y l t i n d i l a u r a t e i n m e t h y l a m y l k e t o n e u n d e r a n i n e r t atmosphere. A f t e r t h e a d d i t i o n o f t h e a l c o h o l , t h e r e a c t i o n was heated a t 60-80°C f o r 2 hours. For half-blocked diisocyanates pre p a r e d f r o m t e r t i a r y a l c o h o l s , t h e h e a t i n g p e r i o d was r e p l a c e d w i t h room t e m p e r a t u r e s t i r r i n g f o r 24-36 h o u r s to p r e v e n t u n d e s i r a b l e s i d e reactions. C h a i n E x t e n d a b l e U r e t h a n e M o d i f i e d Epoxy O l i g o m e r . The c h a i n e x t e n d a b l e u r e t h a n e m o d i f i e d o l i g o m e r s w e r e p r e p a r e d by c o m b i n i n g e q u i m o l a r amounts of e p o x y - d i o l a d d u c t and h a l f - b l o c k e d d i i s o c y a n a t e s , and h e a t i n g the r e s u l t i n g m i x t u r e a t 80°C f o r 4-6 h o u r s u n t i l the i s o c y a n a t e i n f r a r e d band d i s a p p e a r e d . Type I Urea-Urethane O l i g o m e r s . To 30g (0.5 m o l e ) e t h y l e n e d i a m i n e a n d 10g d i m e t h o x y e t h a n e i n a t h r e e - n e c k f l a s k e q u i p p e d w i t h a n o v e r h e a d s t i r r e r was a d d e d o v e r a o n e - h o u r p e r i o d , 1 8 5 g ( 0 . 5 m o l e ) o f butanol half-blocked diisocyanate. A f t e r the a d d i t i o n , the r e a c t i o n w a s s t i r r e d o v e r n i g h t a t room t e m p e r a t u r e . Type II Urea-Urethane Oligomers. To 11.6g (0.1 mole) o f m e l t e d 1 , 6 - h e x a n e d i a m i n e was a d d e d 7 6 . 9 g o f t - b u t a n o l h a l f - b l o c k e d isophorone diisocyanate. D u r i n g about a 30-minute a d d i t i o n , the tem p e r a t u r e r o s e to 5 0 - 6 0 ° C . A f t e r a n a d d i t i o n a l one h o u r o f h e a t i n g a t 5 0 - 6 0 ° C , t h e o l i g o m e r s o l u t i o n was t h i n n e d w i t h 4 0 g o f 2 - h e x o x y ethanol. Primer Formulations. C o a t i n g s were f o r m u l a t e d u s i n g s t a n d a r d t e c h niques. M i l l b a s e s w e r e p r e p a r e d by d i s p e r s i n g t h e o l i g o m e r s o l u t i o n w i t h pigments ( s i l i c a , c a r b o n b l a c k , t i t a n i u m d i o x i d e and b a r i u m s u l f a t e i n a 1:1:1:10 r a t i o ) . T h e v i s c o s i t y o f t h e f o r m u l a t i o n was r e d u c e d to s p r a y v i s c o s i t y by a d d i t i o n o f s o l v e n t . Corrosion Test Procedures. T e s t c o a t i n g samples were a p p l i e d to c o l d r o l l e d , u n p o l i s h e d b a r e s t e e l p a n e l s and b a k e d . S a l t spray tests w e r e c o n d u c t e d a c c o r d i n g t o ASTM m e t h o d B117 u s i n g a S i n g l e t o n c o r r o s i o n t e s t c a b i n e t operated a t 35°C. C o n d e n s i n g h u m i d i t y t e s t s (ASTM D 2 2 4 6 a n d D 2 2 4 7 ) w e r e c o n d u c t e d u s i n g a C l e v e l a n d H u m i d i t y c a b i n e t (Q P a n e l Company). T h e c a t h o d i c p o l a r i z a t i o n t e s t was u s e d t o e v a l u a t e the r e s i s t a n c e of the c o a t i n g s to c o r r o s i o n g e n e r a t e d h y d r o x i d e . A d e t a i l e d d e s c r i p t i o n of t h i s e x p e r i m e n t has been g i v e n e l s e w h e r e ( 3 ) .


10.

HOLUBKA


Results

and

Chain Extendable Oligomers

119

Discussion

Urethane Modified Epoxy-diol Oligomers. Urethane modified e p o x y - d i o l o l i g o m e r s a r e e a s i l y p r e p a r e d by r e a c t i n g t h e f r e e i s o c y a n a t e f u n c t i o n a l group of a h a l f - b l o c k e d d i i s o c y a n a t e w i t h the e p o x y - d i o l adduct. A l t h o u g h the o l i g o m e r formed i n t h i s r e a c t i o n i s u n d o u b t e d l y a m i x t u r e , s i n c e the i s o c y a n a t e c o u l d r e a c t w i t h any o f the h y d r o x y g r o u p s on t h e e p o x y - d i o l a d d u c t , i t i s e x p e c t e d t h a t t h e p r e d o m i n a t e r e a c t i o n w o u l d o c u r a t the most a c c e s s i b l e l o c a t i o n ο the e p o x y - d i o l a d d u c t , namely the t e r m i n a l h y d r o x y f u n c t i o n a l i t y . The r e a c t i v e o l i g o m e r f o r m e d i n t h i s r e a c t i o n w o u l d t h u s be e n d - c a p p e d w i t h a b l o c k e d - i s o c y a n a t e and a h y d r o x y g r o u p . D u r i n g the c u r e , d e b l o c k i n g o f the b l o c k e d - i s o c y a n a t e g e n e r a t e s a f r e e i s o c y a n a t e t h a t s u b s e q u e n t l y r e a c t s w i t h hydroxy f u n c t i o n a l i t y to c h a i n extend the o l i gomer and f o r m a h i g h e r m o l e c u l a r p o l y u r e t h a n e p o l y m e r h a v i n g p e n d a n t hydroxy f u n c t i o n a l i t y . I n f r a r e d s p e c t r o s c o p y was u s e d t o s t u d y t h e mechanism of c h a i n e x t e n s i o n f o r a t o l u e n e d i i s o c y a n a t e m o d i f i e d hyantoin epoxy/2-ethyl-l,3-hexanediol oligomer. S p e c t r a were o b t a i n e d f o r s a m p l e s b a k e d 30 m i n u t e s a t t e m p e r a t u r e s o f 5 0 - 1 8 0 ° C . T h e m e c h a n i s m o f c h a i n e x t e n s i o n was s t u d i e d by o b s e r v i n g t h e OH a n d NH a b s o r p t i o n s a t 3 4 6 0 cm-1 a n d 3 3 4 0 cm-1 r e s p e c t i v e l y . S i n c e one h y d r o x y m o i e t y i s c o n s u m e d f o r e a c h c h a i n e x t e n s i o n w h i l e one u r e t h a n e NH i s f o r m e d , t h e r a t i o o f OH/NH i n f r a r e d a b s o r p t i o n s will d e c r e a s e as c h a i n e x t e n s i o n o c c u r s . The r e s u l t s of t h i s s t u d y a r e s h o w n i n T a b l e I a n d F i g u r e 1. F i g u r e s l a a n d l b show t h e OH a n d NH i n f r a r e d b a n d s o f t h e o l i gomer as a f u n c t i o n of t e m p e r a t u r e i n u n c a t a l y z e d and c a t a l y z e d formulations. T h e u n c a t a l y z e d u r e t h a n e m o d i f i e d e p o x y o l i g o m e r shows o n l y s m a l l c h a n g e s i n t h e OH/NH a b s o r b a n c e r a t i o a t t e m p e r a t u r e s b e l o w 1 6 5 ° C ; o n l y a b o u t a 60% c o n v e r s i o n o f t h e b l o c k e d i s o c y a n a t e was o b s e r v e d . I n c o n t r a s t , sample of the o l i g o m e r c a t a l y z e d w i t h 0 . 5 % d i b u t y l t i n d i l a u r a t e shows n e a r l y c o m p l e t e c h a i n e x t e n s i o n a t t e m p e r a t u r e s as low as 130°C. Two t y p e s o f u r e - u r e t h a n e o l i g o m e r s w e r e p r e p a r e d . The a l c o h o l u s e d t o b l o c k t h e d i i s o c y a n a t e d i s t i n g u i s h e s t h e two t y p e s o f u r e a urethane oligomers. Type I oligomers were prepared u s i n g a d i i s o c y a n a t e h a l f - b l o c k e d w i t h primary or secondary a l c o h o l s ; Type II o l i g o m e r s were prepared u s i n g d i i s o c y a n a t e s h a l f - b l o c k e d w i t h t e r tiary alcohols. W e l l c u r e d f i l m s ( h a v i n g good s o l v e n t r e s i s t a n c e ) a r e o b t a i n e d when u r e a - u r e t h a n e o l i g o m e r s a r e combined w i t h epoxy r e s i n s and baked w i t h o u t e x t e r n a l c r o s s l i n k i n g a g e n t s ( e . g . melamine crosslinker). C u r r e n t e v i d e n c e i n d i c a t e s t h a t the cure c h e m i s t r y i s c o m p l e x and d i f f e r s w i t h changes i n u r e a - u r e t h a n e s t r u c t u r e . Type I Oligomers. Model s t u d i e s i n d i c a t e t h a t the c u r e mechanism of Type I oligomers i n v o l v e an i n i t i a l c h a i n e x t e n s i o n r e s u l t i n g from the r e a c t i o n of an o x i r a n e f u n c t i o n a l i t y of the epoxy r e s i n w i t h i s o c y a n a t e f u n c t i o n a l i t y ( g e n e r a t e d as a r e s u l t of t h e r m a l d e b l o c k i n g of the urethane m o i e t y i n the u r e a - u r e t h a n e o l i g o m e r ) to form a p o l y o x a zolidone. The p o l y o x a z o l i d o n e formed as a r e s u l t of o l i g o m e r c h a i n e x t e n s i o n h a s b e e n f o u n d t o c r o s s l i n k t h r o u g h t h e r e a c t i o n o f N-H f u n c t i o n a l i t y on the backbone of the f o r m i n g p o l y m e r w i t h e x c e s s deblocked urea-urethane oligomer to form b i u r e t c r o s s l i n k s . Figures 2 a a n d 2b show t h e i n f r a r e d s p e c t r a o f b a k e d a n d u n b a k e d T y p e I


120

REACTIVE OLIGOMERS Table I .

Percent Catalyst

Temperature °C

AOH^NH

A

0

50

0.651

Β

0

130

0.589

C

0

150

0.536

D

0

165

0.519

Ε

0

180

0.385

F

0.5

50

0.702

G

0.5

130

0.438

H

0.5

180

0.440

Experiment


Infrared Study of the Chain Extension Reaction

Fig. 1A

Fig. 1B

Figure 1. Infrared spectra for a toluene diisocyanate modified hydantoin epoxy/2-ethy1-1,3-hexanediol oligomer showing the OH and NH bands of the oligomer as a function of temperature in uncatalyzed and catalyzed formulations.


10.

HOLUBKA

121



urea-urethane/epoxy formulations r e s p e c t i v e l y . The p r i n c i p a l d i f f e r e n c e s i n the s p e c t r a i n v o l v e a s i g n i f i c a n t b r o a d e n i n g and s h i f t i n g o f the c a r b o n y l a b s o r p t i o n to h i g h e r f r e q u e n c y ( i n f r a r e d a b s o r p t i o n s a t 1830-1840 cm-1, c o n s i s t e n t w i t h the f o r m a t i o n of o x a z o l i d o n e and biuret moieties). Also consistent with oxazolidone formation is a d i s a p p e a r a n c e o f t h e e p o x y a b s o r p t i o n a t 910 c m - 1 . Type II Oligomers. The c u r e mechanism o f T y p e I I o l i g o m e r s r e l i e s on the thermal decomposition of t e r t i a r y carbamates ( r e a c t i o n products of t e r t i a r y alcohols w i t h isocyanates) that affords carbon d i o x i d e , a l k e n e and f r e e amine. In c o a t i n g f o r m u l a t i o n s Type II oligomers are a l s o f o r m u l a t e d w i t h epoxy r e s i n s . Gas c h r o m a t o g r a p h i c e v i d e n c e i n d i c a t e s t h a t amine i s l i b e r a t e d from the t e r t i a r y carbamate d u r i n g the c u r e and c r o s s l i n k s the c o a t i n g t h r o u g h an epoxy amine r e a c t i o n . T h e c u r e c h e m i s t r y o f a T y p e I I u r e a - u r e t h a n e / e p o x y f o r m u l a t i o n was a l s o s t u d i e d by i n f r a r e d s p e c t r o s c o p y . The r e s u l t s ( F i g u r e 3 and Table II) show d e c r e a s e s i n t h e i n t e n s i t y o f t h e u r e t h a n e a b s o r p t i o n a t 1700 cm-1 a n d t h e d i s a p p e a r a n c e i n t h e e p o x y b a n d a t 910 cm-1 a s the temperature of the cure r e a c t i o n i s i n c r e a s e d from 50-180°C. T h e s e r e s u l t s a r e c o n s i s t e n t w i t h t h e gas c h r o m a t o g r a p h i c d a t a . Also n o t e d i n the i n f r a r e d s p e c t r a i s an i n c r e a s e i n the urea a b s o r p t i o n a t 1630 cm-1 a s t h e t e m p e r a t u r e i s i n c r e a s e d . In t h i s l a t t e r case, t h e f r e e a m i n e r e a c t s w i t h i s o c y a n a t e ( l i b e r a t e d by n o r m a l d e b l o c k i n g of a blocked isocyanate) to generate urea l i n k a g e s ) .

Table II.

I n f r a r e d A b s o r p t i o n D a t a on t h e C u r e o f ( t - B u t y l Carbamate) Terminated Urea-Urethane C o a t i n g a

Absorption

Temperature

A1700/ A1365

A1630/ A1365

Ration

A910/ A1365

A910/ A830

A1630/ A830

50

.95

1.6

.45

.68

1.43

150

.91

2.0

.38

.63

1.52

180

.83

2.6

0

0

3.26

aCoating t-Butyl

c o m p o s i t i o n c o n s i s t s o f 80 w e i g h t p e r c e n t 1 , 6 - h e x a n e d i a m i n e b l o c k e d isophorone d i i s o c y a n a t e based urea urethane r e s i n .

'Absorbance r a t i o s s tandards.

used peaks a t

1365

cm"*

1

a n d 830

cm"

1

as

internal


REACTIVE OLIGOMERS

MICRONS


6.0

1800

7.0

1600

8.0

1400

9.0

1200

IΟ

1000

12

14

800

cm"'

F i g u r e 2. Infrared urea-urethane/epoxy

s p e c t r a of baked and unbaked Type formulations respectively.

'630

c m

I

-l

F i g u r e 3. I n f r a r e d s p e c t r a f o r Type II urea-urethane/epoxy f o r m u l a t i o n s , r e s p e c t i v e l y , showing d e c r e a s e s i n the i n t e n s i t y of t h e u r e t h a n e a b s o r p t i o n as the* t e m p e r a t u r e o f the c u r e r e a c t i o n i s increased from 50-180°C.


10.

HOLUBKA


123


Conclusion An a l t e r n a t e a p p r o a c h t o h i g h s o l i d s c o a t i n g f o r m u l a t i o n s has been presented. The synthesis of three r e a c t i v e oligourethanes incorpora t i n g chemical f u n c t i o n a l i t y that allows chain extension to occur d u r i n g c u r e i n a r e a c t i o n i n d e p e n d e n t o f c r o s s l i n k i n g has been described. The proposed c h a i n e x t e n s i o n r e a c t i o n o c c u r i n g t o generate, i n s i t u , during cure, a conventional high molecular weight polymer that i s subsequently c r o s s l i n k e d w i t h usual c r o s s l i n k i n g agents. One r e a c t i v e o l i g o m e r i n c o r p o r a t e s b l o c k e d i s o c y a n a t e - p o l y o l c h e m i s t r y t h a t undergoes c h a i n e x t e n s i o n , d u r i n g c u r e , t o form hydroxy f u n c t i o n a l polyurethanes that a r e subsequently c r o s s l i n k e d , i n s i t u , with conventional aminoplast crosslinkers. T h e r e m a i n i n g two r e a c t i v e oligomers use blocked isocyanage-epoxy and t - b u t y l carbamateepoxy c h e m i s t r y f o r c h a i n e x t e n s i o n and subsequent s e l f - c r o s s l i n k i n g through f o r m a t i o n o f the corresponding o x a z o l i d o n e and epoxy-amine linkages respectively.

Literature Cited 1. 2. 3.

Lee, E. "Epoxy Resins," American Chemical Society, Washington D.C., 1970. Wicks, Z. W. Progress in Organic Coatings, 3, pp. 73-99 (1975). Wiggle, R. R.; Smith, A. G . ; and Petrocelli, J . V. Paint Tech., 40, 174 (1968).

RECEIVED February 19, 1985


Reactive Oligomers - American Chemical Society

Recommend Documents