Characterization of the Cure of Diether-Linked Phthalonitrile Resins

26 Characterization of the Cure of Diether-Linked Phthalonitrile Resins

Downloaded by STANFORD UNIV GREEN LIBR on October 1, 2012 | http://pubs.acs.org Publication Date: August 12, 1982 | doi: 10.1021/bk-1982-0195.ch026

R. Y. TING Naval Research Laboratory, Orlando, FL 32856 T. M. KELLER, T. R. PRICE, and C. F. PORANSKI, JR. Naval Research Laboratory, Washington, DC 20375 New organic resin systems are in constant demand because of the increasing use of fiber-reinforced organic matrix composites to replace metallic components in weight-critical aerospace and advanced marine applications. High temperature capability, low moisture absorption, and improved storage and processing properties are emphasized for new composite matrix materials. Diether-linked phthalonitrile resins recently developed at NRL promise to meet these requirements and are being evaluated as potential candidates for such applications. The linking structure R in the monomers include bisphenol-A, bisphenol-S, bisphenol-A6F, resorcinol, hydroquinone and dihydroxybiphenol. The results of the characterization of cured phthalonitrile resins are presented. This includes their thermal properties from thermal gravimetric analysis and differential scanning calorimetry, spectroscopic properties from the infra-red and nuclear magnetic resonance techniques, and mechanical properties from torsional pendulum analysis and fracture mechanics evaluation. Compared to conventional m e t a l l i c s t r u c t u r a l m a t e r i a l s , f i b e r - r e i n f o r c e d organic matrix composites have a very high s p e c i f i c modulus and t e n s i l e s t r e n g t h . For t h i s reason, they are being used i n many aerospace and marine systems i n which weight r e d u c t i o n i s an important c o n s i d e r a t i o n . This r e d u c t i o n i s e s p e c i a l l y c r i t i c a l f o r the s u c c e s s f u l development of new v e r t i c a l and short take-off and landing (V/STOL) a i r c r a f t i n order to compensate f o r the large engines r e q u i r e d f o r v e r t i c a l l i f t . Composite m a t e r i a l s have been used s u c c e s s f u l l y , and convent i o n a l matrix m a t e r i a l s such as epoxies are being considered f o r a p p l i c a t i o n i n V/STOL systems. Epoxy polymers, however, s u f f e r many shortcomings. They a r e extremely s e n s i t i v e to moisture absorption, which causes a l a r g e r e d u c t i o n i n t h e i r g l a s s This chapter not subject to U.S. copyright. Published, 1982, American Chemical Society

In Cyclopolymerization and Polymers with Chain-Ring Structures; Butler, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

POLYMERS


338

WITH

CHAIN-RING

STRUCTURES

t r a n s i t i o n temperature, thus l i m i t i n g t h e i r maximum use to temperatures l e s s than approximately 135°C i n a wet environment. Furthermore, epoxy prepregs r e q u i r e c o l d storage a t a l l times and are t h e r e f o r e d i f f i c u l t to handle, c o s t l y to s t o r e , and suscept i b l e to chemical degradation. Because of the complex chemistry and v a r i a t i o n s i n formulation of epoxy r e s i n s , p r o v i d i n g q u a l i t y a n a l y s i s and c o n t r o l f o r these r e s i n s presents a s e r i o u s problem f o r l a r g e q u a n t i t y , m u l t i - b a t c h procurements, e s p e c i a l l y those i n v o l v i n g s e v e r a l manufacturers. As a r e s u l t of these problems, new organic r e s i n s are being sought to meet o p e r a t i o n a l r e q u i r e ments at higher temperatures, to be r e l a t i v e l y i n s e n s i t i v e to moisture, and to provide improved room-temperature storage prop e r t i e s and p r o c e s s a b i l i t y equivalent to the s t a t e - o f - t h e - a r t expoxies. In recent years, research e f f o r t s at the Naval Research Laboratory have l e d to the development of a new c l a s s of r e s i n s c a l l e d p h t h a l o n i t r i l e s (1), which seem to provide the d e s i r e d p r o p e r t i e s f o r advanced composite a p p l i c a t i o n s . The r e s i n that has a diamide s t r u c t u r e w i t h an eight-carbon a l i p h a t i c chain l i n k a g e , c a l l e d the C-10 monomer, has been s t u d i e d e x t e n s i v e l y and s u c c e s s f u l l y demonstrated to be a p o t e n t i a l m a t r i x m a t e r i a l (2). The C-10 polymer e x h i b i t e d long-term s t a b i l i t y at temperatures up to 245°C (_3), and i t s moisture uptake i s l e s s than that of epoxies or polyimides ( 4 ) . The r e s i n monomer a l s o represents a chemically simple and pure system f o r easy q u a l i t y c o n t r o l (5), and i s v i r t u a l l y i n e r t at room temperature f o r easy storage and handling (2). U n f o r t u n a t e l y , the s y n t h e t i c procedure f o r the C-10 p h t h a l o n i t r i l e r e s i n i n v o l v e s a r e a c t i o n that has r e l a t i v e l y low y i e l d , and r e q u i r e s expensive s t a r t i n g m a t e r i a l s . Continued e f f o r t s to overcome these d i f f i c u l t i e s have been s u c c e s s f u l , however, and a s e r i e s of second-generation p h t h a l o n i t r i l e r e s i n s with d i e t h e r - l i n k i n g s t r u c t u r e have been developed (6). In t h i s r e p o r t , the r e s u l t s of the c h a r a c t e r i z a t i o n and the cure of these new m a t e r i a l s w i l l be presented. Experimental Material. The d e t a i l of the synthesis of d i e t h e r - l i n k e d p h t h a l o n i t r i l e r e s i n s has been given i n an e a r l i e r report (6). B r i e f l y , a mixture of b i s p h e n o l , 4 - n i t r o p h t h a l o n i t r i l e and an excess amount of anhydrous potassium carbonate s t i r r e d i n dry dimethyl s u l f o x i d e r e s u l t e d i n p h t h a l o n i t r i l e monomers:

H0R0H + 2 0 N 2

CN

K C0

CN

DMSO

2

CN

NC 3

CN

NC

HEAT POLYMER


26.

TING ET A L .

Cure of Diether-Linked Phthalonitrile Resins

339


The HOROH component may be bisphenol-A, bisphenol-S, dihydroxyb i p h e n y l , r e s o r c i n o l , hydroquinone or bisphenol-A6F:

These r e s i n s have been shown to e x h i b i t even b e t t e r p r o p e r t i e s than the f i r s t - g e n e r a t i o n p h t h a l o n i t r i l e s i n terms of thermal and o x i d a t i v e s t a b i l i t y and moisture s e n s i t i v i t y . But, most important of a l l , t h i s new r e a c t i o n pathway i s s h o r t and simple, and takes advantage of inexpensive s t a r t i n g m a t e r i a l s . Thus, i t seems to have opened up p o s s i b i l i t i e s f o r designing polymers with a wide v a r i e t y of s t r u c t u r a l v a r i a t i o n s , and f o r lowering the m a t e r i a l cost to make the r e s i n s competitive w i t h other e x i s t i n g composite matrix systems. Thermal A n a l y s i s . D i f f e r e n t i a l scanning c a l o r i m e t r y (DSC) was c a r r i e d out f o r a l l r e s i n s u s i n g a Perkin-Elmer DSC-2 system. The scanning was performed over the temperature range of 27°C to 267 C at a h e a t i n g r a t e of 20°C/min under a dry n i t r o g e n atmosphere. Thermogravimetric a n a l y s i s (TGA) was a l s o c a r r i e d out f o r cured r e s i n s by using a DuPont 900 S e r i e s u n i t . Samples were analyzed over the temperature i n t e r v a l of 20°C to 700°C by determining sample weight l o s s as a f u n c t i o n of temperature a t a heating r a t e of 10°C/min w h i l e continuously purged with dry nitrogen. e

T o r s i o n a l Pendulum A n a l y s i s (TPA). A f r e e l y o s c i l l a t i n g t o r s i o n a l pendulum (7) operating at ca. 1 Hz was used f o r the determination of dynamic shear modulus of a l l cured samples as a f u n c t i o n of temperature. The procedure recommended i n ASTM-D-2236-70 was f o l l o w e d . F r a c t u r e Energy. The f r a c t u r e energy of cured p h t h a l o n i t r i l e samples was measured by u s i n g standard compact t e n s i o n specimens (8). A precrack was always introduced at the end of the saw-cut with a r a z o r blade. Specimens were f r a c t u r e d i n an INSTRON a t a crosshead speed of 0.125 cm/min. The c r i t i c a l f a i l u r e l o a d was


POLYMERS WITH CHAIN-RING

340

STRUCTURES

measured and polymer f r a c t u r e energy determined by using the equation of Schultz ( 9 ) .


R e s u l t s and D i s c u s s i o n DSC r e s u l t s of uncured d i e t h e r - l i n k e d p h t h a l o n i t r i l e r e s i n s , shown i n Figure 1A, i n d i c a t e d a s i n g l e melting peak f o r an i n i t i a l scan. The melting temperatures so determined ranged from 199°C f o r the bisphenol-A l i n k e d r e s i n to 234°C f o r the bisphenol-A6F r e s i n . Each repeated DSC scan always showed an exotherm at about 127°C (see F i g u r e IB) or a lower temperature, i n d i c a t i v e of the formation of a meta-stable c r y s t a l l i n e phase upon h e a t i n g and c o o l i n g . Furthermore, m u l t i p l e , broadened melting was evident during the second scan, a s i t u a t i o n s i m i l a r to that observed i n a l i p h a t i c - l i n k e d p h t h a l o n i t r i l e r e s i n s that was "B"-staged i n prepregging operations ( 2 ) . T h i s thermal behavior may be used to develop proper degree of B-staging f o r prepregs of these r e s i n s . The B"-staged prepolymer i s nonr e a c t i n g a t room temperature, an appealing f e a t u r e of these m a t e r i a l s f o r the p r e p a r a t i o n of prepregs. Neat p h t h a l o n i t r i l e monomers normally were polymerized by m e l t i n g the r e s i n and then continuously h e a t i n g them i n a i r a t 280°C f o r 6 days. The r e l a t i v e thermal s t a b i l i t i e s i n a i r of the cured r e s i n s were s t u d i e d by h e a t i n g the sample i s o t h e r m a l l y and observing the weight l o s s . No observable weight l o s s was found a f t e r heating a t 250 C f o r 1000 hours. At 280°C, the b i p h e n y l l i n k e d polymer e x h i b i t e d only 1.6% weight l o s s a f t e r 3200 hours. The next most s t a b l e polymer was that formed from r e s o r c i n o l , followed by bisphenol-S, bisphenol-A and b i s p h e n o l A6F i n that order. TGA r e s u l t s , shown i n F i g u r e 2, a l s o i n d i c a t e d that no weight l o s s could be detected f o r any polymer up to 300°C. As the temperature was f u r t h e r i n c r e a s e d , r e s p e c t i v e weight l o s s data showed that the b i p h e n y l - l i n k e d polymer was again the most s t a b l e m a t e r i a l , whereas the bisphenol-S l i n k e d polymer was the l e a s t s t a b l e of the four systems s t u d i e d . The water a b s o r p t i v i t y of cured r e s i n s was found to depend g r e a t l y on the l i n k i n g s t r u c t u r e R. P o l a r groups i n the l i n k i n g s t r u c t u r e are expected to a t t r a c t water. The r e s u l t s of g r a v i m e t r i c measurements, shown i n F i g u r e 3, i n d i c a t e d that the bisphenol-A and bisphenol-A6F l i n k e d polymers had v e r y low a f f i n i t y f o r water, absorbing l e s s than 1.5% water on immersion. On the other hand, the bisphenol-S l i n k e d polymer absorbed more water (up to 3.5%), which may be a t t r i b u t e d to the presence of the p o l a r s u l f o n e group. F i g u r e 4 shows the TPA r e s u l t s f o r the bisphenol-A and the bisphenol-S l i n k e d polymers cured at 280°C f o r s i x days. Both the dynamic shear modulus and the mechanical l o s s f a c t o r are g i v e n as a f u n c t i o n of temperature from -150 C to about +300°C. During a TPA run, a temperature scan covering the complete g l a s s - t o rubber t r a n s i t i o n could not be achieved because the sample softened as the g l a s s t r a n s i t i o n temperature, Tg, was approached. M

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Differential scanning calorimetry of a bisphenol-A phthalonitrile resin.




342

Figure 2.

Thermogravimetric analysis results of various diether-linked phthalo nitrile resins cured for 6 days at 280°C.

OL

Figure 3.

STRUCTURES

I 400

I 800

I I I 1200 1600 2000 TIME (HOURS)

I 2400

I 2800

Water absorption of various phthalonitrile polymers. Key: Π» bisphenol S; Δ , bisphenol A; and O , bisphenol A6F.


26.

TING

E T AL.


343

Therefore, i n t h i s study T was taken as the temperature a t which the modulus decreased r a p i d l y with a corresponding i n c r e a s e i n the v a l u e of the l o s s f a c t o r . This was u s u a l l y the p o i n t where the TPA experiment had t o be terminated due to sample s o f t e n i n g . In a d d i t i o n t o the g l a s s t r a n s i t i o n process, two secondary r e l a x a t i o n processes i n the g l a s s y s t a t e were observed a t approximately -50 C and +150 C, r e s p e c t i v e l y . The peak a t -50°C may be a t t r i b u t e d t o the e f f e c t of absorbed water (10). The peak i n t e n s i t y i s only 0.04, as opposed to 0.1 f o r the cured C-10 p h t h a l o n i t r i l e (11). T h i s i s another i n d i c a t i o n that the d i e t h e r - l i n k e d p h t h a l o n i t r i l e r e s i n s are l e s s s e n s i t i v e to moisture than the diamide-linked systems. The dynamic l o s s curve f o r the C-10 polymer (11) a l s o showed a t r a n s i t i o n a t -130°C, r e l a t e d to the molecular motions of the amide l i n k a g e s and the a l k y l c h a i n between them. T h i s peak was not observed i n the d i e t h e r - l i n k e d polymers, presumably because the aromatic l i n k a g e s are more r i g i d and would not a l l o w i n t r a - c h a i n segmental motions to take p l a c e a t such a low temperature. The r e l a x a t i o n peak a t 150°C i s s i m i l a r t o that found i n the C-10 polymer cured a t 240°C f o r f i v e days (11). The o r i g i n of t h i s peak i s s t i l l unknown a t the present time. The mechanical p r o p e r t i e s i n c l u d i n g the f r a c t u r e energy, bending modulus, shear modulus and the g l a s s t r a n s i t i o n temperature of the polymers a r e shown i n Table I . The p r o p e r t i e s of a t e t r a f u n c t i o n a l epoxy (Narmco 5208), cured according to a manufacturer's suggested procedure, a r e a l s o i n c l u d e d i n Table I f o r comparison. Although the cured phthalon i t r i l e r e s i n s a r e only m a r g i n a l l y tougher than the epoxy and comparable i n s t i f f n e s s , they o f f e r h i g h e r use temperature ( o r Tg). The e x c e p t i o n a l case was the bisphenol-A6F l i n k e d r e s i n , which i s extemely b r i t t l e and has a very low g l a s s t r a n s i t i o n temperature. g


e

e

Based on these r e s u l t s , some p h t h a l o n i t r i l e r e s i n s were e l i m i n a t e d from f u r t h e r study. The bisphenol-S p h t h a l o n i t r i l e r e s i n was not considered because of i t s high water a b s o r p t i v i t y . The m e l t i n g p o i n t of hydroquinone-linked monomers was higher than that of the other r e s i n s . The t e x t u r e , c o l o r and s o l u b i l i t y of t h i s compound a l s o v a r i e d from batch to batch although the m e l t i n g temperature and IR and proton nmr s p e c t r a were n e a r l y i d e n t i c a l . The bisphenol-A6F compound was q u i t e a t t r a c t i v e based on i t s thermal s t a b i l i t y and water up-take. However, the precursor m a t e r i a l f o r the s y n t h e s i s of t h i s monomer i s no longer a v a i l a b l e . The mechanical p r o p e r t i e s of dihydroxybiphenyl p h t h a l o n i t r i l e d i d not represent any improvement over those of the bisphenol-A polymer. The TGA r e s u l t showed that the b i p h e n y l polymer was more s t a b l e , as expected from i t s l i n k i n g s t r u c t u r e , but the precursor was much more expensive than bisphenol-A. Based on the c o n s i d e r a t i o n s of modulus, g l a s s t r a n s i t i o n temperature, thermal s t a b i l i t y , water a b s o r p t i v i t y as w e l l as m a t e r i a l c o s t , i t was decided to examine f u r t h e r the p r o p e r t i e s of bisphenol-A l i n k e d phthalonitrile resin.



344

POLYMERS

Table I .

Linking Structure

WITH CHAIN-RING STRUCTURES

Room Temperature Mechanical P r o p e r t i e s o f Cured P h t h a l o n i t r i l e Resins Fracture Energy (J/m ) 2

Bending Modulus (GN/m ) 2

Shear Modulus (GN/m ) 2

T

g

.(C)

Bis-A

99

3.92

1.20

320

Bis-S

202

2.25

1.32

300

Bi-phenyl

140

4.35

1.22

300

Bis-A6F

53

4.02

1.25

225

5208 Epoxy

76

3.89

1.25

260

90:10 mixture*

60

5.18

1.74

246

*90% bisphenol-A p h t h a l o n i t r i l e and 10% bisphenol-A.



26.

TING E T A L .


345

The p o l y m e r i z a t i o n of any p h t h a l o n i t r i l e r e s i n could be i n i t i a t e d by simply heating the r e s i n monomer a t a temperature higher than i t s melting temperature. However, as was i n d i c a t e d e a r l i e r , the neat p o l y m e r i z a t i o n of bisphenol-A l i n k e d phthalon i t r i l e r e s i n r e q u i r e d s e v e r a l days of continuous heating a t 260-290°C before a v i s c o s i t y i n c r e a s e became d e t e c t a b l e i n the melt. Extended post-cure was a l s o necessary f o r the development of adequate mechanical s t r e n g t h , because extremely pure phthalon i t r i l e r e s i n was stubbornly r e s i s t a n t t o p o l y m e r i z a t i o n . In order to reduce the cure time, b i s p h e n o l compounds were used as coreactants i n the p o l y m e r i z a t i o n r e a c t i o n s . The r e s u l t s i n d i cated that as long as the i n i t i a t i n g agent and the monomer were compatible, both the temperature and the time f o r g e l a t i o n could be g r e a t l y diminished. The mechanisms i n v o l v e d i n t h i s a c c e l erated cure were discussed i n a recent r e p o r t (12). It is b e l i e v e d that bisphenol probably attacks the n i t r i l e groups of the p h t h a l o n i t r i l e monomer to a f f o r d i n i t i a l l y an 1 - a r y l o x y i s o i n d o l e n i n e u n i t , which r e a c t s with other n i t r i l e groups to form polymeric m a t e r i a l s . OR ROH +

Mixtures of the bisphenol-A l i n k e d r e s i n monomer and bisphenol-A coreactant i n v a r i o u s molar r a t i o s were prepared and DSC analyses c a r r i e d out. The r e s u l t s suggested that a 90:10 mixture sample was most acceptable, and the DSC scan f o r such a sample i s shown i n F i g u r e 5. A weak endotherm a t 137°C i n d i c a t e s the presence of bisphenol-A c o r e a c t a n t , whereas the p o s i t i o n of the melting peak of the monomer i s p r a c t i c a l l y unchanged from that of the neat r e s i n (Figure 1A). A f t e r staging the sample a t 277°C f o r 30 minutes, an isothermal time-scan on DSC showed the appearance of an exotherm, i n d i c a t i n g the i n i t i a t i o n of p o l y m e r i z a t i o n a f t e r an i n d u c t i o n p e r i o d of about 15 minutes. T h i s mixture sample was heated a t 210°C f o r 48 hours with g e l a t i o n o c c u r r i n g i n l e s s than 24 hours ( i . e . o v e r n i g h t ) . TGA r e s u l t s i n d i c a t e d that a post-cure of the sample a t 250°C f o r 46 hours produced a polymer which had a lower r a t e of decomposition than that from the neat p o l y m e r i z a t i o n of 6 days a t 280°C. An i n f r a - r e d s p e c t r o s c o p i c technique, developed by M a r u l l o and Snow (13), was used to monitor the time r e q u i r e d f o r the disappearance of the C=N group as an


346

POLYMERS WITH CHAIN-RING STRUCTURES

i n d i c a t i o n of the advancement of the cure. T h i s r e s u l t i s given i n Table I I , where the e f f e c t of added bisphenol-A i n a c c e l e r a t i n g the cure of bisphenol-A p h t h a l o n i t r i l e i s e v i d e n t . Carbon-13 nmr s p e c t r a were a l s o obtained f o r t h i s mixture i n perdeutero-dimethyl s u l f o x i d e (DMSO-dfc). Samples of the mixture were heated f o r 3.5 and 7 hours at 200 C, cooled and ground to a f i n e powder form. 200-mg p o r t i o n s of the powder samples were then d i s s o l v e d i n 2 ml of DMSO-d£. The r e s i n mixture was then heated a t 200°C f o r 3, 5 and 7 hours w h i l e s t i r r e d i n 2 ml of DMSO-d^. Not a l l of the r e a c t e d m a t e r i a l d i s s o l v e d , however. The aromatic carbon r e g i o n of the carbon-13 nmr spectrum of an unheated sample i s shown i n F i g u r e 6. The four l i n e s marked w i t h arrows are from the bisphenol-A r e s i n . The r e l a t i v e i n t e n s i t i e s do not n e c e s s a r i l y r e f l e c t the r e l a t i v e c o n c e n t r a t i o n of the two components. But the i n t e n s i t i e s of these f o u r l i n e s d i d decrease with the heating time of the mixture u n t i l a f t e r 7 hours they were b a r e l y observable. The DMS0-d£ s o l u t i o n s of the heated mixtures were i n t e n s e l y green, i n d i c a t i v e of the presence of some type of r e a c t i o n product. However, no new l i n e s were evident i n the s p e c t r a of the heated samples. T h i s f a c t was a t t r i b u t e d to very low c o n c e n t r a t i o n s of s o l u b l e r e a c t i o n products, below the l e v e l r e q u i r e d f o r carbon-13 nmr d e t e c t i o n .


e

Mechanical t e s t data f o r the 90:10 mixture sample cured a t 210°C f o r 48 hours f o l l o w e d by a two day post cure a t 250°C were i n c l u d e d i n Table I. Although the TGA r e s u l t seemed to i n d i c a t e t h i s to be a d e s i r a b l e cure schedule, the r e s u l t i n g polymer was d e f i n i t e l y too b r i t t l e . Post-cure at 250°C was a l s o i n s u f f i c i e n t i n p r o v i d i n g a g l a s s t r a n s i t i o n temperature higher than that of the epoxy sample. Furthermore, bisphenol-A was proven to be too v o l a t i l e a t the r e q u i r e d cure temperatures of higher than 200 C. To a l l e v i a t e these problems, new polyphenols have been synthesized and are p r e s e n t l y being evaluated as p o t e n t i a l c u r i n g agents: e

HO

where n=3 or 9. TGA r e s u l t s of samples of bisphenol-A phthalo n i t r i l e cured w i t h the polyphenols at 250 C f o r 21-48 hours, followed by approximately one day post c u r i n g at 280°C, are shown i n F i g u r e 7 (curves Β and C). Compared to neat bisphenol-A p h t h a l o n i t r i l e cured f o r 7 days at 280°C (curve A), they v o l a t i l i z e d a t a g r e a t e r r a t e a t lower temperatures. However, the r a t e decreased as temperature i n c r e a s e d and a t 700 C there was about 12% more weight r e s i d u e . Furthermore, i t should a l s o be noted that h i g h molecular weight e l a s t o m e r i c polymeric m a t e r i a l s c o n t a i n i n g p o l y s u l f o n e - e t h e r l i n k a g e s and terminated by ether u n i t s are commercially a v a i l a b l e . The approach e

e



26.

TING

ET

347


AL.

I

1

1

1

1

1

1

1

1

1

350

370

390

410

430

450

470

490

510

530

1

550

TEMPERATURE (°K) Figure 5.

Differential scanning calorimetry of a 90/10 sample mixture of bis phenol-A phthalonitrile and bisphenol-A.

Table I I .

IR Monitoring of the Cure of Bisphenol-A P h t h a l o n i t r i l e Resins Time (hours) r e q u i r e d f o r 50% l o s s of C=N

Sample

75% l o s s of C=N

Neat r e s i n cured at 300 C

27

43

Neat r e s i n cured at 280°C

62

240

7

12

e

90:10 mixture* sample cured at 210°C

*90% bisphenol-A p h t h a l o n i t r i l e and 10% bisphenol-A.

American Chemical Society Library 1155 16th St.Chain-Ring N . «r. Structures; Butler, G., et al.; In Cyclopolymerization and Polymers with ACS Symposium Series; American Chemical Washington, DC, 1982. Washington. 0. Π Society: ΜΜΜΑ


348


STRUCTURES

»• ' 150

Figure 6.

1

' ι 100

125

Aromatic portion of the NMR spectrum of an unheated mixture sample.

lOOr-S r90 80 UJ 3 o

ο 70 Lu

or Lu Ο ο: Lu CL

60 50 h 40h H r

NITROGEN ATMOSPHERE HEATING RATE = I0 C/MIN. J

300

ι

I

ι

L

400 500 TEMPERATURE (°C)

600

700

Figure 7. Thermogravimetric analysis results of bisphenol-A phthalonitrile resins cured for 7 days at 280°C (A), 22 h at 250°C and 22 h at 280°C with 15% poly phenol (B), and 48 h at 250°C and 24 h at 280°C with 20% polyphenol (C).



26.

TING ET A L .


349

presented here t h e r e f o r e suggests that i t would be p o s s i b l e to economically produce a corresponding rubbery, h i g h temperature s t a b l e polyphenol. Such a polyphenol, i n a d d i t i o n to e x p e d i t i n g the cure of bisphenol-A l i n k e d p h t h a l o n i t r i l e monomers, could a l s o generate small e l a s t o m e r i c domains f o r the toughening of the base r e s i n . S i m i l a r approaches i n v o l v i n g the r e a c t i o n of e i t h e r CTBN or ATBN rubbers w i t h epoxy r e s i n s have been used to toughen epoxy polymers (14). When used as composite matrix m a t e r i a l s , the rubber-modified r e s i n s a l s o show d i s t i n c t advan tages i n improving the p r o c e s s a b i l i t y and b o n d a b i l i t y and i n i n c r e a s i n g the f a t i g u e design l i m i t of the composite (15). Acknowledgement This work was sponsored by the Naval A i r Systems Command. The authors g r a t e f u l l y acknowledge the a s s i s t a n c e of Paul Peyser, Robert L. C o t t i n g t o n and Harry C. Nash i n p o r t i o n s of the experimental work.

Literature Cited 1. Griffith, J. R., O'Rear, J. G., and Walton, T. R. in "Copolymers, Polyblends. and Composites", ed. N. A. Platzer, Advances in Chem. Ser. of ACS, 1975, 142, 458. 2. Ting, R. Y. and Nash, H. C., Polym. Eng. Sci., 1981, 21, 441. 3. Walton, T. R., Griffith, J. R. and O'Rear, J. G. in "Adhesion Science and Technology", Polym. Sci. Tech., ed. L. H. Lee, Plenum Press, Ν. Y., 1975, Vol. 9, p. 655. 4. Bascom, W. D., Bitner, J. L., and Cottington, R. L. in "High Performance Composites and Adhesives for V/STOL Aircraft", ed. L. B. Lockhart, Jr., NRL Memo Rept. 4005, Washington, DC (May 1979). 5. Poranski, C. F. and Moniz, W. B., in "Resins for Aerospace," ed. C. A. May, Am. Chem. Soc. Symp. Ser., 1980, 132, 337. 6. Keller, T. M. and Griffith, J. R., ACS Organic Coat. Plast. Chem. Preprint, 1979, 40, 781. 7. Nelson, L. E., Mechanical Properties of Polymers and Compo sites, Dekker, Ν. Y., 1974. 8. Knott, J. F., Fundamentals of Fracture Mechanics, Butter worths, England, 1973. 9. Schultz, W., in Fracture Mechanics of Aircraft Structures, ed. H. Liebowitz, AGARDograph, AGARD Rept. AG-176, NTIS, Springfield, VA, 1974. 10. Gillham, J. Κ., ACS Organic Coat-Plast. Chem. Preprint, 1978, 38, 598. 11. Bascom, W. D., Cottington, R. L., and Ting, R. Y., J. Materials Sci., 1980, 15, 2097. 12. Keller, Τ. Μ., Price, T. R., and Griffith, J. R., ACS Org. Coat. Plast. Chem. Preprint, 1980, 43, 804.


POLYMERS WITH CHAIN-RING STRUCTURES

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13. Marullo, N. P. and Snow, Α., ACS Polymer Preprint, 1981, 22, 46. 14. Riew, C. K., Rowe, Ε. Η., and Siebert, A. R., in Toughness and Brittleness of Plastics, ed. Dennin and Crugnola, ACS Advances in Chemistry Series, 1976, 154, 326. 15. Moulton, R. J. and Ting, R. Y., to appear in the Proc. Int'l Conf. Composite Structutes, Sept. 16-18, 1981, Paisley, Scotland. December 15, 1981.


RECEIVED


Characterization of the Cure of Diether-Linked Phthalonitrile Resins

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