13 Curing Kinetics of Unsaturated Polyester and Vinyl Ester Resins Downloaded by UNIV OF CINCINNATI on February 18, 2015 | http://pubs.acs.org Publication Date: August 29, 1982 | doi: 10.1021/bk-1982-0227.ch013
CHANG DAE HAN and KWOK-WAI LEM Department of Chemical Engineering, Polytechnic Institute of New York, Brooklyn, NY 11201 Unsaturated polyester r e s i n s are one of the most important thermosetting r e s i n s used f o r preparing molding compounds f o r hot-press matched molding, cold molding, and contact molding. Polyester r e s i n s o f commercial i n t e r e s t , containing carbon-to-carbon double bonds, are generally c l a s s i f i e d i n t o three types: Alkyds, p o l y a l l y l esters, and l i n e a r unsaturated polyesters. Alkyd r e s i n s , which are prepared from polyhydric alcohols and d i b a s i c acids o r t h e i r corresponding anhydrides, together with modifying oils o r t h e i r corresponding acids, f i n d extensive use in surface coatings. Both p o l y a l l y l e s t e r s and l i n e a r unsaturated polyester r e s i n s are used p r i m a r i l y i n moldings and c a s t i n g s . P o l y a l l y l e s t e r s are prepared from the monomers der i v e d from the reactions o f allyl e s t e r s o f d i b a s i c acids or t h e i r corresponding anhydrides, the most important monomers being diallyl phthalates and diallyl isophthalates. The molded a r t i c l e s produced with diallyl phthalates are generally expensive and therefore f i n d use in s p e c i a l a p p l i c a t i o n s , such as i n manufacturing e l e c t r i c a l components r e q u i r i n g good e l e c t r i c i n s u l a t i o n and dimensional s t a b i l i t y (1). On the other hand, the l i n e a r unsaturated polyester r e s i n s f i n d use in many commercial a p p l i c a t i o n s , such as in producing solventless lacquers, and thermos e t t i n g molding compounds. The r e s i n is normally prepared by the reaction o f a saturated diol with a mixture o f an unsaturated d i b a s i c a c i d and a 'modifying' d i b a s i c a c i d or its corresponding anhydride. I t is commonly r e f e r r e d to as 0097-6156/83/0227-0201$06.25/0 © 1983 American Chemical Society In Chemorheology of Thermosetting Polymers; May, C.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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POLYMERS
' c o n v e n t i o n a l u n s a t u r a t e d p o l y e s t e r , and t y p i c a l examples a r e b i s p h e n o l A - f u m a r i c a c i d p o l y e s t e r and isophthalic polyester* C o m m e r c i a l l y , the r e s i n i s a v a i l a b l e i n t h e form o f s o l u t i o n s c o n t a i n i n g 60-70 w t . % o f a prepolymer d i s s o l v e d i n a r e a c t i v e s o l v e n t (e.g., styrene). The c o n v e n t i o n a l p o l y e s t e r r e s i n s r e i n f o r c e d w i t h g l a s s f i b e r s a r e u s e d i n r o o f i n g and b u i l d i n g i n s u l a t i o n , automobiles, paneling for l o r r i e s , and b o a t h u l l s (.2). As i l l u s t r a t e d i n T a b l e I , i n c o n v e n t i o n a l p o l y e s t e r r e s i n s , t h e e s t e r groups and c a r b o n - t o - c a r b o n d o u b l e bond l i n k a g e s a r e l o c a t e d a l o n g t h e polymer c h a i n s , t h u s r e f e r r e d t o as s t r u c t o p e n d a n t (3), and t h e y a r e d i s t r i b u t e d randomly i n t h e p o l y m e r network a f t e r t h e p o l y m e r has been c r o s s l i n k e d w i t h s t y r e n e . The c u r e d r e s i n s a r e r i g i d , h e a t s t a b l e , and have good c h e m i c a l r e s i s t a n c e t o most i n o r g a n i c and o r g a n i c a c i d s and, a l s o , t o a wide range o f o r g a n i c solvents. However, t h e e s t e r g r o u p s and t h e u n r e a c t e d c a r b o n - t o - c a r b o n d o u b l e bonds i n t h e n e t work p r o v i d e s i t e s f o r h y d r o l y t i c a t t a c k , o x i d a t i o n , and/or halogenation. T h i s makes t h e c u r e d r e s i n u n s u i t a b l e f o r use i n a g g r e s s i v e e n v i r o n m e n t s (1,2) . To overcome t h e s e d r a w b a c k s , i n r e c e n t y e a r s much a t t e n t i o n h a s been p a i d t o t h e development o f r e s i n s w h i c h c a n be f a b r i c a t e d w i t h t h e same p r o c e s s e s as t h o s e f o r c o n v e n t i o n a l p o l y e s t e r r e s i n s , but having superior p r o p e r t i e s . Vinyl ester resins a r e t h e r e s u l t o f s u c h development e f f o r t s ( 4 - 6 ) . V i n y l e s t e r r e s i n s are a d d i t i o n products o f v a r i o u s e p o x i d e r e s i n s and e t h y l e n i c a l l y u n s a t u r a t e d monocarboxylic acids (5). I t combines t h e e x c e l l e n t m e c h a n i c a l , c h e m i c a l and s o l v e n t r e s i s t a n c e o f epoxy r e s i n s w i t h t h e p r o p e r t i e s found i n t h e u n s a t u r a t e d polyester resins. In g e n e r a l , the cured v i n y l e s t e r r e s i n has p h y s i c a l p r o p e r t i e s s u p e r i o r to the cured conventional ester r e s i n , p a r t i c u l a r l y corrosion resistance. T h i s a r i s e s from t h e d i f f e r e n c e s i n t h e number and arrangement o f p o l a r groups s u c h as e s t e r and h y d r o x y l g r o u p s and c a r b o n - t o - c a r b o n d o u b l e bonds p r e s e n t i n the polymer c h a i n s . As i l l u s t r a t e d i n T a b l e I , i n t h e v i n y l e s t e r r e s i n s , t h e e s t e r g r o u p s and c a r b o n - t o - c a r b o n d o u b l e bond l i n k a g e s a r e l o c a t e d a t t h e end o f t h e p o l y m e r
In Chemorheology of Thermosetting Polymers; May, C.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
In Chemorheology of Thermosetting Polymers; May, C.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
Resin
Vinyl Ester
Unsaturated Polyester Resin
Resin
C-C-C-0
Js
1 H
η «3-6
0 C-OH
Structopendant group for thickening
t
OH
1
p^v^-wU—o-c-c = c c=o
Γ «
