33 Novel Masked Aliphatic Diisocyanates HENRI ULRICH
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Donald S. Gilmore Research Laboratories, The Upjohn Company, North Haven, CT 06473
Blocked aliphatic diisocyanates are used in light stable one-component polyurethane systems. Typical examples include baking enamels, wire coatings and powder coatings. A variety of active hydrogen containing compounds have been used as blocking agents, notably oximes and phenol.(1) Heating of the blocked isocyanates generates the free isocyanates with release of the blocking agent. Attempts have been made over the years to develop blocking agents which are incorporated into the polymer backbone upon thermal release, thereby eliminating the need for well-ventilated working areas. A l l these efforts have met with failure. We selected a novel approach to design a masked or blocked aliphatic diisocyanate based on the fact that 1,3-disubstituted ureas undergo facile thermal dissociation to produce an isocyanate and an amine derivative.(2) In the dissociation of mono acyl and aroyl ureas an isocyanate and a carboxylic acid amide is simultaneously produced. If the urea group is part of a cyclic system both fragments are parts of the same molecule. The required novel bifunctional monomers are synthesized by reacting cyclic ureas with aliphatic or aromatic dicarboxylic acid chlorides in the presence of triethylamine as hydrogen chloride scavenger. This r e a c t i o n i s b e s t conducted i n an i n e r t o r g a n i c s o l v e n t u s i n g an excess o f the c y c l i c urea t o prevent polymer f o r m a t i o n (Scheme I ) . The c y c l i c ureas are s y n t h e s i z e d from the corresponding diamines and carbon d i o x i d e o r c a r b o n y l s u l f i d e . ( 3 ) The eiethtmembered r i n g c y c l i c urea can be obtained from caprolactam.^2) The s t a b i l i t y o f the d i f u n c t i o n a l monomers i n a l c o h o l s o r p o l y o l s was demonstrated by the f a c t t h a t no r i n g opening was observed upon r e f l u x i n g i n lower b o i l i n g a l c o h o l s . Heating of the d i f u n c t i o n a l monomers i n o-dichlorobenzene produces the corresponding a l i p h a t i c d i i s o c y a n a t e s as evidenced by i n f r a r e d spectroscopy and t r a p p i n g w i t h methanol t o g i v e biscarbamates.(3)
0097-6156/81/0172-0519$05.00/0 © 1 9 8 1 American Chemical Society
Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
520
URETHANE
CHEMISTRY AND APPLICATIONS
R e c y c l i z a t i o n does n o t o c c u r b e c a u s e t h e r e a c t i o n o f a l i p h a t i c i s o c y a n a t e s w i t h c a r b o x y l i c a c i d amide g r o u p s o c c u r s o n l y u n d e r very severe c o n d i t i o n s . SCHEME Synthesis of
I
Difunctional Macrocyclic
Ureas
^ M>)r^ n ^
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W
l
i
EtoN Cl
R
CI
+
2 HN
NH
Nt^ Y 0
V 0
0 ^
œ
2 )
n
^
^
ΗΝ
Ρ
Nr^ 0
R=lvJJ
Y 0
C
H
2)n^
Ν
NH
Y 0
0
n=3,4,5
-( C H ) 2
?
The r a t e o f r i n g o p e n i n g o f t h e b i s c y c l i c u r e a s was s t u d i e d i n a m o d e l s y s t e m u s i n g n i t r o b e n z e n e as s o l v e n t t o s i m u l a t e a p o l a r environment and to a c h i e v e the n e c e s s a r y h i g h d i s s o c i a t i o n temperatures. B e n z y l a l c o h o l was u s e d as t h e trapping reagent. H e a t i n g t h e m a c r o c y c l i c b i s u r e a based on i s o p h t h a l o y l c h l o r i d e and l , 3 - d i a z e p i n - 2 - o n e w i t h o u t a c a t a l y s t a t 170°C e f f e c t e d a c o n v e r s i o n to the carbamate w i t h i n t e n minutes. C o m p l e t e r e a c t i o n was a c h i e v e d w i t h i n f i v e m i n u t e s i n t h e p r e s e n c e o f t r i e t h y l e n e d i a m i n e (DABC0) and t h e t e m p e r a t u r e c o u l d be l o w e r e d t o 155° i f 0 . 5 mole % ( b a s e d o n t h e b i s c y c l i c u r e a ) o f d i b u t y l t i n d i l a u r a t e ( T - 1 2 ) were u s e d a s c a t a l y s t . The e x t e n t o f r e a c t i o n was m o n i t o r e d b y measurement o f t h e s i g n a l due t o b e n z y l i c p r o t o n s , i n t h e f o r m e d c a r b a m a t e , i n t h e ^H-NMRspectrum.
Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
33.
ULRICH
Masked Aliphatic Diisocyanates
521
SCHEME I I R i n g O p e n i n g Of D i f u n c t i o n a l M a c r o c y c l i c U r e a s
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ΗΝ
Ν
R
Ν
V" V V 0
0
o
Ϊ
0
C H C H 0 ^ H ( CH ) 6
5
2
2
0
Δ
NH(CH ) NCO 9
0
1
n
V
0
Λ
0 C N ( C H ) NH
N H ^ R ^ N H ( 0
NH
C H ) NH 2
n
0CH C H 2
6
5
0
The u t i l i t y o f t h e b i s c y c l i c u r e a s f o r c u r i n g o f c o a t i n g s was d e m o n s t r a t e d b y d i s p e r s i n g them i n a f u n c t i o n a l a c r y l i c p o l y m e r f o r m u l a t e d f o r powder c o a t i n g a p p l i c a t i o n , o r b y u s i n g them a s a d d i t i v e i n s o l v e n t b a s e d c o a t i n g s o r i n aqueous p o l y m e r emulsions f o r e l e c t r o c o a t i n g . To a c h i e v e good c o m p a t i b i l i t y w i t h f u n c t i o n a l ! z e d a c r y l i c a n d e p o x y r e s i n s a b i s c y c l i c u r e a w i t h n=3, a n d R = - ( C H 2 )η( see Scheme I ) was s y n t h e s i z e d . A c r y l i c - a n d e p o x y p o l y m e r s o l u t i o n s were p r e p a r e d u s i n g \ % b y w e i g h t o f t h e b i s c y c l i c urea (based on t h e d r y polymer) and methyl e t h y l ketone as solvent. F i l m s c a s t f r o m t h e s e s o l u t i o n s o n s t e e l s h e e t s were c l e a r , and had a t h i c k n e s s o f ^ 0 . 4 m i l . I n d i c a t e d below a r e the b a k i n g temperatures f o r t h e f i l m s t o become i n s o l u b l e i n m e t h y l e t h y l k e t o n e u s i n g a 30 m i n u t e baking cycle. The r e q u i r e d t e m p e r a t u r e s w e r e l o w e r b y a d d i n g a c a t a l y s t (15% b y w e i g h t b a s e d o n t h e b i s c y c l i c u r e a o f dibutyltin dilaurate). a c r y l i c polymer epoxy polymer
with catalyst 175°C 160°C
without catalyst 195°C 175°C
Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
Downloaded by UNIV OF TEXAS AT DALLAS on March 16, 2017 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch033
522
URETHANE CHEMISTRY AND APPLICATIONS
The g i v e n t e m p e r a t u r e s s e r v e a s a g u i d e l i n e s i n c e t h e y may v a r y w i t h f i l m t h i c k n e s s , c r o s s l i n k e r and c a t a l y s t c o n c e n t r a t i o n s and s o l v e n t . I n t h i s p r o c e s s t h e a l i p h a t i c d i i s o c y a n a t e s a r e formed a n d r e a c t i o n w i t h h y d r o x y l groups a t t a c h e d t o t h e polymer backbone occurs. The r e s u l t i n g c a r b a m a t e l i n k a g e s l e a d t o c r o s s l i n k i n g of the polymer m a t r i x , thus c r e a t i n g tough and s o l v e n t r e s i s t a n t films. The p o l y m e r d e r i v e d f r o m t h e r e a c t i o n o f b i s a c y l a m i d o a l k y l i s o c y a n a t e s w i t h m a c r o g l y c o l s c o n t a i n u r e t h a n e a n d amide groups as w e l l . F u r t h e r work i s i n p r o g r e s s t o o p t i m i z e s o l v e n t f r e e one component s y s t e m s b a s e d o n m a c r o g l y c o l s a n d t h e n o v e l d i f u n c t i o n a l c y c l i c u r e a monomers.
Literature Cited 1.
Wicks, Z. W., Jr., "Blocked Isocyanates", Progress in Organic Coatings, 3, 73 (1975), Elsevier (Neth.).
2.
Ulrich, H., and Sayigh, A.A.R., Angew. Chem., Int. Ed. Engl., 5, 704, 724 (1966).
3.
Ulrich, H., Tucker, Β. and Richter, R., J. Org. Chem. 43, 1544 (1978).
RECEIVED April 30,
1981.
Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
