Chapter 20
Structure—Performance Relationships of Urethane Acrylates JoAnn A. McConnell and F. Kurt Willard Radcure Specialties Inc., 9800 Bluegrass Parkway, Jeffersontown, KY 40299
Acrylated urethanes are an important class of commercial radiation-curable oligomers. Industrial applications of these materials cover a wide range, including binders for magnetic media, vehicles for inks, and coatings for vinyl floor tiles, optical fibers, and paper. The compositions, and therefore, the properties of the acrylated urethanes are varied in order to meet the performance criteria of the different end uses. Properties of various acrylated urethanes will be discussed as they relate to structure.
Radiation curing technology i s rapidly expanding into numerous, commercial applications. Due to t h e i r fast cure response, acrylate functional raw materials dominate the industry. A wide range of acrylated monomers and oligomers i s available i n order to meet the various application requirements. Acrylated oligomers can be divided into three main classes: polyester acrylates, epoxy acrylates, and urethane acrylates. Urethane acrylates are an e s p e c i a l l y important commercial class of oligomers. Applications include binders for magnetic media, vehicles for inks, and coatings for v i n y l f l o o r t i l e s , o p t i c a l f i b e r s , and paper. Each application has certain performance requirements that must be met by the urethane oligomer. This paper w i l l discuss the effect of urethane acrylate composition on end properties. URETHANE ACRYLATES A generic urethane acrylate i s shown i n Figure 1. I t i s formed by the reaction of a diisocyanate with a polyol and a hydroxy a l k y l acrylate. Two types of substructures are found i n urethanes, hard and soft segments. The hard segment i s derived from the diisocyanate and urethane linkages. The soft segment imparts 0097-6156/90/0417-0272$06.00/0 © 1990 American Chemical Society
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f l e x i b i l i t y t o the u r e t h a n e a c r y l a t e , and i s d e r i v e d from the polyol. By v a r y i n g R, D, and Ρ i n F i g u r e 1, a m u l t i t u d e o f composi t i o n s , and t h e r e f o r e p r o p e r t i e s , can be o b t a i n e d . In t h i s study R was l i m i t e d t o h y d r o x y e t h y l a c r y l a t e (HEA) and h y d r o x y p r o p y l a c r y l a t e (ΗΡΑ), and no d i f f e r e n t i a t i o n was made between the two. Three d i i s o c y a n a t e s (D) were s t u d i e d : toluene diisocyanate (TDI), i s o p h o r o n e d i i s o c y a n a t e ( I P D I ) , and d i c y l c o h e x y l m e t h a n e 4,4'-diisocyanate (HMDI). W e a t h e r a b i l i t y i s one c o n s i d e r a t i o n i n the c h o i c e o f a d i i s o c y a n a t e . O l i g o m e r s based on a l i p h a t i c d i i s o c y a n a t e s form c o a t i n g s t h a t weather w e l l , whereas c o a t i n g s based on a r o m a t i c d i i s o c y a n a t e s y e l l o w on exposure.^ The p o s s i b i l i t i e s f o r P, the p o l y o l , a r e v i r t u a l l y u n l i m i t e d . B e s i d e s v a r y i n g the f u n c t i o n a l i t y ( d i - , t r i - , o r t e t r a - o l ) , a number of d i f f e r e n t backbones c a n be employed: polyether, polyester, poly caprolactone, or polycarbonate. The s u b s t r u c t u r e and m o l e c u l a r weight can a l s o be changed. Only d i - and t r i - h y d r o x y p o l y e t h e r s and p o l y e s t e r s were used i n t h i s s t u d y . B e s i d e s v a r y i n g the n a t u r e o f R, D, and P, the r e l a t i v e r a t i o s of t h e s e t h r e e components c a n a l s o be changed. These changes i n s t o i c h i o m e t r y a l l o w m o l e c u l a r w e i g h t , degree o f u n s a t u r a t i o n , and u r e t h a n e c o n t e n t t o be v a r i e d . One o t h e r c o m p o s i t i o n a l v a r i a b l e t h a t must be c o n s i d e r e d i n u r e t h a n e d e s i g n i s i l l u s t r a t e d i n F i g u r e s 1 and 2. The u r e t h a n e a c r y l a t e shown i n F i g u r e 1 i s the t h e o r e t i c a l r e a c t i o n p r o d u c t o f 4 eq. o f d i i s o c y a n a t e w i t h 2 eq. o f HEA/HPA and 2 eq. o f p o l y o l . I n p r a c t i c e , t h r e e d i f f e r e n t t y p e s o f u r e t h a n e s a r e always o b t a i n e d from t h i s r e a c t i o n ^ (see F i g u r e 2 ) . The d i s t r i b u t i o n o f t h e s e t h r e e p r o d u c t s i s dependent on s t o i c h i o m e t r y . To summarize, T a b l e I l i s t s t h e ways t h a t t h e c o m p o s i t i o n o f u r e t h a n e a c r y l a t e s can be a l t e r e d , and the p r o p e r t i e s t h a t may be a f f e c t e d by t h e s e changes. Each o f t h e s e p r o p e r t i e s w i l l be d i s c u s s e d as they r e l a t e t o c o m p o s i t i o n .
TABLE I COMPOSITIONAL VARIABLES AND END PROPERTIES OF URETHANE ACRYLATES
Compositional
Variables
p o l y o l type d i i s o c y a n a t e type functionality m o l e c u l a r weight & distribution urethane content
End
Properties
viscosity cure speed tensile strength t e n s i l e modulus elongation hardness adhesion flexibility solvent resistance
274
RADIATION CURING OF POLYMERIC MATERIALS
0
0
0
0
II
II
II
II
CH -CH-R-0-C-NH-D-NH-C-0-P-0-C-NH-D-NH-C-0-R-CH=CH L i l . soft I segment hard segment 2
Figure 1. Generic urethane acrylate i n which R = hydroxy a l k y l acrylate backbone, D = diisocyanate backbone, and Ρ = polyol backbone.
0
0
II
II
CH =CH-R-0-C-NH-D-NH-C-0-R-CH=CH 2
2
capped
diisocyanate
0
0
0
0
II
II
II
II
CH =CH-R-0-C-NH-D-NH-C-0-P-0-C-NH-D-NH-C-0-R"CH=CH 2
2
urethane acrylate
0
0
0
II
II
II
CH =CH-R-0-C-NH-D-NH-C-0-P-0-C-NH 2
0
0
II
II
o
D
II
CH =CH-R-0-C-NH-D-NH-C-0-P-0-C-NH extended urethane acrylate 2
Figure 2. Experimental reaction products of urethane formation i n which R = hydroxy a l k y l acrylate backbone, D = diisocyanate backbone, and Ρ = polyol backbone.
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EXPERIMENTAL The a c r y l a t e d u r e t h a n e s were s y n t h e s i z e d by a d d i n g HEA o r ΗΡΑ to a d i i s o c y a n a t e i n the p r e s e n c e o f a c a t a l y s t and p o l y m e r i z a t i o n inhibitor. A f t e r a s u i t a b l e h o l d t i m e , p o l y o l was added, and the r e a c t i o n h e l d f o r c o m p l e t i o n (200 5
Ν
L i n e a r P o l y e t h e r 1800 1900 Branched P o l y ether
HB 2H
0 0
5 75
40 >200
Within
each c o m p o s i t i o n ,
R, D, and t h e s t o i c h i o m e t r y a r e i d e n t i c a l ;
Ρ i s difunctional.
TABLE X I I EFFECT OF ACRYLATE FUNCTIONALITY ON COATING PROPERTIES Composition^(th. func.)
Mol Wt Wt/Double (th) Bond ( t h )
Adhesion S o l . R e s i s t . Conical Pencil (MEK D.R.) Hardness B e n d ( i n ) (%)
F (2.0) (2.4) (2.6)
1800 2300 1700
900 965 650
HB Β F
1/4 0 0
0 10 10
90 >200 >200
Ε
1600 1500
777 652
3H 2H
1/4 0
0 0
10 50
(2.06) (2.3)
J-Within each c o m p o s i t i o n , R, D, and t h e s t o i c h i o m e t r y a r e i d e n t i c a l ; Ρ i s c h e m i c a l l y t h e same, and i s a m i x t u r e o f d i o l and t r i o l , o n l y the r a t i o o f d i o l t o t r i o l changes.
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Structure-Performance Relationships
TABLE X I I I EFFECT OF MOLECULAR WEIGHT AND/OR URETHANE CONTENT ON COATING PROPERTIES Comp
1
1
Mol Wt (th)
Adhesion Conical Wt/Urethane Pencil L i n k a g e ( t h ) Hardness B e n d ( i n ) (%)
Sol. Resist. (MEK D.R.)
10 2
>200 >200
1/4 1/4
0 0
10 5
HB 2B 4B
1/2 1/4 1/4
25 50 95
4 2 2
300 317 325
2H 2H H
3 0 0
75 75 40
>200 >200 180
2600 7000
650 875
HB 2B
3/4 1/4
50 5
5 3
1500 2300
375 380
H HB
0 0
2 0
100 145
D
1400 1500
350 375
2H 2H
0 0
Ε
1600 2500
400 625
3H HB
Ρ
3000 5000 7000
750 830 875
Η
1200 1900 2600
I
J
C o m p o s i t i o n . W i t h i n those c o m p o s i t i o n s w i t h t h e same s t o i c h i o m e t r y , R and D a r e i d e n t i c a l , and Ρ has t h e same c h e m i c a l s t r u c t u r e and f u n c t i o n a l i t y , but with d i f f e r e n t molecular weights. Only the s t o i c h i o m e t r y changes f o r t h e o t h e r c o m p o s i t i o n s : R, D, and Ρ a r e the same.
CONCLUSION The c o m p o s i t i o n o f u r e t h a n e a c r y l a t e s can be v a r i e d i n o r d e r t o a c h i e v e c e r t a i n end p r o p e r t i e s r e q u i r e d by t h e i n t e n d e d a p p l i c a t i o n . The s t r u c t u r e - p r o p e r t y r e l a t i o n s h i p s d i s c u s s e d i n t h i s paper can p r o v i d e guidance i n t h e i n t e l l i g e n t d e s i g n o f t h i s c l a s s o f r a d i a t i o n cure oligomer. LITERATURE 1. 2.
CITED
H. C. Miller, Rad. Curing, 11(2), B. Martin, Rad. Curing, 13(3), 5
RECEIVED
September 13, 1989
4 (1984). (1986).
