The Effects of Radiation on High-Technology Polymers - American

Chapter 15

Radiation-Resistant, Amorphous, All-Aromatic Poly(arylene ether sulfones) Synthesis, Physical Behavior, and Degradation Characteristics 1,3

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2,4

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Downloaded by UNIV OF BATH on July 1, 2016 | http://pubs.acs.org Publication Date: December 13, 1989 | doi: 10.1021/bk-1989-0381.ch015

D. A. Lewis , James H. O'Donnell , J. L. Hedrick , T. C. Ward , and J . E. McGrath 2,5

1

Polymer and Radiation Group, Department of Chemistry, University of Queensland, St. Lucia, Brisbane 4067, Australia Polymer Materials and Interfaces Laboratory, Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 2

An aromatic polysulfone based on 4,4'-biphenol and 4,4'-dichlorodiphenyl sulfone (Bp PSF) was shown to be the most resistant of a systematic series of poly (arylene ether sulfones) to Co gamma irradiation. Sulfur dioxide was the major volatile product and was used as a probe to correlate the radiation resistance with polymer structure. The use of biphenol in the polymer reduced G(SO ) by 60% compared with bisphenol A based systems (Bis-A PSF). Surprisingly, the isopropylidene group was shown to be remarkably radiation resistant. The ultimate tensile strain decreased with dose for all polysulfones investigated and the rate of decrease correlated well with the order of radiation resistance determined from volatile product measurements. The fracture toughness (K ) of Bis-A PSF also decreased with irradiation dose, but the biphenol based system maintained its original ductility. 60

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IC

There is an increasing need for the production of light, very strong polymeric based matrix resins, adhesives and composite structures which can withstand harsh environments such as UV and ionizing radiation. High performance engineering thermoplastics such as aromatic polysulfones and polyether ketones are strong candidates for this application since they are easy to process, have high maximum service temperature, good modulus and fracture toughness characteristics. An extended service life is required to render such structures economically viable, thus it is necessary 3

Current address: Watson Research Center, IBM Corporation, Yorktown Heights, NY 10598 Current address: Almaden Research Center, IBM Corporation, San Jose, CA 95120-6099 Address correspondence to this author.

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0097-6156/89/0381-0252$06.00/0 1989 American Chemical Society ©

Reichmanis and O'Donnell; The Effects of Radiation on High-Technology Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


15.

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Poly(arylene ether sulfones)

253

to o p t i m i z e r a d i a t i o n r e s i s t a n c e while s t i l l m a i n t a i n i n g the r e q u i r e d mechanical p r o p e r t i e s . Two a r o m a t i c p o l y s u l f o n e s which a r e c u r r e n t l y a v a i l a b l e c o m m e r c i a l l y have been shown (1,2) t o be r e s i s t a n t t o i o n i z i n g r a d i a t i o n , making t h i s c l a s s o f polymers s u i t a b l e f o r e n g i n e e r i n g a p p l i c a t i o n s i n these harsh environments. There have been r e l a t i v e l y few s y s t e m a t i c s t u d i e s o f t h e r e l a t i o n s h i p between polymer s t r u c t u r e and r a d i a t i o n r e s i s t a n c e f o r polymers w i t h a r o m a t i c backbones. Such i n v e s t i g a t i o n s a r e n e c e s s a r y t o d e t e r m i n e which l i n k a g e s a r e t h e most s u s c e p t i b l e t o r a d i a t i o n d e g r a d a t i o n . The p a u c i t y of d a t a i s due, i n p a r t , t o t h e d i f f i c u l t i e s i n s y n t h e s i z i n g a s e r i e s of polymers w i t h c o n t r o l l e d s t r u c t u r e and m o l e c u l a r w e i g h t . Thus, t h e s y n t h e s i s of t h e new polymers was an i m p o r t a n t p a r t of t h i s work. A l l of t h e polymers a r e l i n e a r w i t h no l o n g c h a i n b r a n c h i n g and are a l l p a r a substituted. These v a r i a b l e s have been shown t o have i m p o r t a n t e f f e c t s on the r a d i a t i o n r e s i s t a n c e . F u r t h e r m o r e , the polymers have s i m i l a r m o l e c u l a r weights and m o l e c u l a r weight d i s t r i b u t i o n s , which a l l o w the comparison of t h e change i n m e c h a n i c a l p r o p e r t i e s w i t h r a d i a t i o n and polymer s t r u c t u r e t o be a more d e f i n e d structure/property investigation. The p r o d u c t i o n of v o l a t i l e p r o d u c t s upon i r r a d i a t i o n can r e s u l t i n the u n d e s i r a b l e f o r m a t i o n of b u b b l e s . T h i s can l e a d t o t h e premature f a i l u r e of s t r e s s e d components, t h u s l i m i t i n g s e r v i c e life. The y i e l d of v o l a t i l e p r o d u c t s a f t e r i r r a d i a t i o n has been demonstrated t o be a s e n s i t i v e probe of t h e r e l a t i v e r a d i a t i o n r e s i s t a n c e f o r model compounds such as c y c l o h e x a n e and benzene, w i t h G ( H ) = 5.6 (3) and 0.038 ( 4 ) , respectively. The m e c h a n i c a l p r o p e r t i e s e x h i b i t e d by a polymer a f t e r i r r a d i a t i o n a r e a complex f u n c t i o n of m o l e c u l a r weight and m o l e c u l a r weight d i s t r i b u t i o n and the number and t y p e of new s t r u c t u r e s formed. Thus, i t i s d i f f i c u l t t o draw s t r u c t u r e / r a d i a t i o n r e s i s t a n c e c o n c l u s i o n s from t h e change i n t h e m e c h a n i c a l p r o p e r t i e s a l o n e . However, t h e changes i n m e c h a n i c a l p r o p e r t i e s a r e d i r e c t i n d i c a t i o n s o f t h e u l t i m a t e u s e f u l n e s s of t h e polymer i n a r a d i a t i o n environment. In t h i s paper, we examine t h e r e l a t i o n s h i p between r a d i a t i o n r e s i s t a n c e and polymer s t r u c t u r e u s i n g v o l a t i l e p r o d u c t and m e c h a n i c a l p r o p e r t y measurements. 2

Experimental The polymers used i n t h i s s t u d y were p r e p a r e d by a n u c l e o p h i l i c a c t i v a t e d a r o m a t i c s u b s t i t u t i o n r e a c t i o n of a b i s p h e n a t e and d i h a l o d i p h e n y l s u l f o n e (j>). The r e a c t i o n was c a r r i e d out i n an a p r o t i c d i p o l a r s o l v e n t (NMP) a t 170°C i n t h e p r e s e n c e o f p o t a s s i u m c a r b o n a t e (Scheme 1) ( 5 , 6 ) . The polymers were p u r i f i e d by r e p e a t e d p r e c i p i t a t i o n i n t o methanol/water, f o l l o w e d by d r y i n g t o c o n s t a n t weight. The b i s p h e n o l s used were b i s p h e n o l - A ( B i s - A ) , hydroquinone (Hq) and b i p h e n o l ( B p ) . Thus, the a l i p h a t i c c h a r a c t e r o f B i s - A c o u l d be removed w h i l e r e t a i n i n g a s i m i l a r a r o m a t i c c o n t e n t and structure. The use o f b i p h e n o l a l l o w s an i n v e s t i g a t i o n of t h e p o s s i b l e e f f e c t of extended c o n j u g a t i o n on t h e r a d i a t i o n degradation.


254

EFFECTS OF RADIATION ON HIGH-TECHNOLOGY POLYMERS

Scheme 1 HO—X-OH

NMP/Toluene K C0 ,


2

3

170°C

The p o l y ( a r y l e n e e t h e r s u l f o n e s ) comprise s t r i c t l y a l t e r n a t i n g b i s p h e n o l and d i p h e n y l s u l f o n e u n i t s . S i m i l a r l y , "copolymers" were p r e p a r e d u s i n g two d i f f e r e n t b i s p h e n o l s , which produced a s t a t i s t i c a l sequence w i t h t h e a l t e r n a t i n g d i p h e n y l s u l f o n e u n i t s . The c o m p o s i t i o n a n d ^ t r u c t u r e s o f t h e s e polymers were c h a r a c t e r i z e d by H and C ΝMR and i n f r a r e d s p e c t r o s c o p y t o c o n f i r m t h a t l i n e a r , a l l p a r a s u b s t i t u t e d polymers were formed. GPC measurements were used t o demonstrate t h a t a monomodal m o l e c u l a r weight d i s t r i b u t i o n w i t h a p o l y d i s p e r s i t y o f a p p r o x i m a t e l y 2 was o b t a i n e d . The g l a s s t r a n s i t i o n temperature was d e t e r m i n e d on a P e r k i n - E l m e r DSC-2 u s i n g a h e a t i n g r a t e o f 10 C/min and t h e i n t r i n s i c v i s c o s i t y was determined i n NMP a t 25°C. These d a t a a r e summarized i n T a b l e I . The t e c h n i q u e used f o r v o l a t i l e p r o d u c t a n a l y s i s was based on the q u a n t i t a t i v e t r a n s f e r o f v o l a t i l e s m a l l m o l e c u l e s which a r e produced by r a d i o l y s i s o f the polymer onto a GC column where t h e y a r e s e p a r a t e d , i d e n t i f i e d and d e t e r m i n e d q u a n t i t a t i v e l y , as d e s c r i b e d i n d e t a i l e a r l i e r ( 7 ) . A weighed sample ( c a . 40 mg) o f polymer was e v a c u a t e d and s e a l e d i n a t h i n w a l l e d g l a s s ampoule (approx. 20mm χ 2mm diam) a f t e r s l o w l y h e a t i n g under vacuum t o 200°C o v e r 24 hours t o remove adsorbed water. A f t e r i r r a d i a t i o n , t h e ampoule was heated i n t h e s p e c i a l l y d e s i g n e d i n j e c t i o n p o r t (8) of a H e w l e t t P a c k a r d 5730 A gas chromatograph a t 150°C f o r 15 min p r i o r t o b e i n g c r u s h e d by a p l u n g e r . The gases were c a r r i e d from the i n j e c t i o n p o r t onto a Chromosorb 102 column (3m x3mm) u s i n g h e l i u m c a r r i e r gas and then t o a t h e r m a l c o n d u c t i v i t y d e t e c t o r and e


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Table I Polysulfone Characterization r

Polymer

[Tll


B i s - A PSF Hq PSF Bp PSF Hq/Bp(50) PSF

i25°C NMP

0.50 1.40 1.00 0.71

Tg/°C 190 217 232 217

flame i o n i z a t i o n d e t e c t o r c o n n e c t e d i n s e r i e s . The GC c o n d i t i o n s were o p t i m i z e d t o g i v e b a s e l i n e r e s o l u t i o n between s u c c e s s i v e peaks, e n a b l i n g i d e n t i f i c a t i o n of low m o l e c u l a r weight gases and a c c u r a t e peak a r e a d e t e r m i n a t i o n . C a l i b r a t i o n p l o t s o f peak a r e a v e r s u s gas volume were e s t a b l i s h e d u s i n g pure g a s e s . Dogbone samples were c u t from compression molded t h i n s h e e t s . They were b u n d l e d t o g e t h e r i n groups of f o u r between g l a s s m i c r o s c o p e s l i d e s (1 mm t h i c k ) t o e l i m i n a t e t h e e f f e c t o f non u n i f o r m d i s t r i b u t i o n of secondary e l e c t r o n s ( 9 ) . Samples f o r f r a c t u r e toughness measurements and t h e dogbone b u n d l e s were then s e a l e d i n Pyrex tubes £ j i 9 under h i g h vacuum t o 150°C t o remove a i r and water. Co gamma i r r a d i a t i o n was conducted w i t h dose r a t e s of a p p r o x i m a t e l y lOkGyh as d e t e r m i n e d by extended F r i c k e Dosimetry. Ampoules f o r v o l a t i l e p r o d u c t s t u d i e s were i r r a d i a t e d a t 150±1°C i n an aluminum b l o c k h e a t e r which was c o n t r o l l e d by a Eurotherm temperature c o n t r o l l e r . T h i s temperature was s e l e c t e d s i n c e i t was near t h e maximum s e r v i c e t e m p e r a t u r e f o r these polymers. I n a d d i t i o n , r e l a t i v e l y s m a l l doses of i r r a d i a t i o n (100-600 kGy) were r e q u i r e d t o o b t a i n e a s i l y q u a n t i f i e d volumes o f g a s e s . F r a c t u r e toughness, Κ , measurements were performed a c c o r d i n g t o ASTM s t a n d a r d E399 on specimens 6.3 mm t h i c k a t a s t r a i n r a t e o f 0.5 mm/min. S t r e s s - s t r a i n measurements were made on an I n s t r o n t e n s i l e t e s t e r a t a s t r a i n r a t e o f 10 mm/min. a

e

r

n

e

a

t

n

Results The major v o l a t i l e p r o d u c t from t h e i r r a d i a t i o n o f B i s - A PSF a t 150°C was s u l f u r d i o x i d e , which was produced w i t h GiSO^) 0.146. T h i s i s c o n s i s t e n t w i t h p r e v i o u s measurements a t 30°C, 125°C and 220°C ( 1 , 2 ) . O t h e r v o l a t i l e p r o d u c t s o b s e r v e d were hydrogen, methane, and c a r b o n d i o x i d e . The G v a l u e s f o r t h e v a r i o u s gaseous p r o d u c t s a r e compared w i t h l i t e r a t u r e r e s u l t s f o r i r r a d i a t i o n a t 30°C i n T a b l e I I . The a p p a r e n t r e d u c t i o n i n GiH^) a t t h e h i g h e r i r r a d i a t i o n temperature used i n t h i s work i s b e l i e v e d t o be an a r t i f a c t due t o a r e d u c t i o n i n t h e h y r o c a r b o n i m p u r i t i e s i n t h e samples used i n t h i s s t u d y compared w i t h t h e work o f Brown and O ' D o n n e l l ( 1 , 2 ) . T h i s i s s u p p o r t e d by t h e absence o f hydrocarbons i n the v o l a t i l e p r o d u c t s a f t e r i r r a d i a t i o n a t 150°C. S i m i l a r l y , t h e water o b s e r v e d i n t h e v o l a t i l e p r o d u c t s a f t e r i r r a d i a t i o n a t ambient t e m p e r a t u r e β


256


Table II G(gas) for Bis-A PSF, Irradiated i n Vacuum 30°C

so

0.02 0.009 0.008

H

2

0.002 0.002 0.0002


CO C

hydrocarbons

3

Totals k

150°C

a

Product

b

0.146

± 0.014

0.0033 0.0050 0.0070 0.0066

± ± ± ±

0.0009 0.0012 0.0019 0.0012

0.163

0.041

from Brown and O'Donnell, réf. 1. errors are estimated at the 95% confidence l e v e l

i s believed to be due to a less rigorous drying procedure employed in that study. It i s unlikely that carbon dioxide would be produced from the degrading polymer since multiple bond fragmentation and reformation would be required. After repeated p r e c i p i t a t i o n of the polymer, G ( C 0 ) decreased markedly while the y i e l d of other products was not affected. I t i s proposed that potassium carbonate, used to generate reactive phenolate during the step growth polymerization, was occluded i n the precipitated polymer and was the primary source of the observed carbon dioxide. Elimination of a methyl r a d i c a l from the isopropylidene group of Bis-A PSF, followed by hydrogen abstraction to form methane might be expected to be an important process, since this i s the only a l i p h a t i c part of t h i s polymer. However, G(CH ) was very small compared with G ( S 0 ) and i t appears that C'CH^ s c i s s i o n i s a r e l a t i v e l y low y i e l d process. This implies that the isopropylidene group i s a r e l a t i v e l y radiation resistant group i n a structure such as bisphenol-A. This conclusion i s supported by ESR and NMR studies (1Ό) which demonstrate that main chain s c i s s i o n also does not occur at this group, at least at neutral pH. The results are contrary to the conclusions of Sasuga (11) (high dose rate electron beam i r r a d i a t i o n i n a i r ) where the radiation resistance of the isopropylidene group was only s l i g h t l y greater than the sulfone linkage. Perhaps the actual i r r a d i a t i o n temperature was quite d i f f e r e n t i n their experiments due to the high dose rates employed. The dependence of the v o l a t i l e product y i e l d with structure can be a very sensitive probe of radiation resistance and the protective e f f e c t of aromatic rings. < ^ observed to decrease from 5.6 to 0.038 for cyclohexane (3) and benzene (4) after gamma i r r a d i a t i o n at ambient temperature. Since a l l polymers under investigation contained the sulfone moiety, G(SO^) (Table III) i s an ideal probe for radiation resistance f o r this s e r i e s . 2

4

2

G

H

w

a

s

2


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Table I I I G(S0 ) f o r Several Poly(Arylene Ether S u l f o n e s ) A f t e r Vacuum I r r a d i a t i o n a t 150°C 2

Polymer


B i s - A PSF Hq PSF Hq/Bp(50) Bp PSF

G(SO

e r r o r s correspond

t o 95%

a

± ± ± ±

0.014 0.011 0.004 0.010

confidence

level

0.146 0.136 0.097 0.063

PSF

)

The r e l a t i v e l y minor r o l e of the i s o p r o p y l i d e n e group i n the r a d i a t i o n d e g r a d a t i o n o f B i s - A PSF was f u r t h e r d e m o n s t r a t e d by the s m a l l d i f f e r e n c e i n G(SO^) f o r B i s - A PSF (0.146) and Hq PSF (0.136), a w h o l l y a r o m a t i c polymer. The s m a l l r e d u c t i o n i n G ( S 0 ) may be due t o a s l i g h t l y h i g h e r a r o m a t i c c o n t e n t i n Hq PSF compared w i t h B i s - A PSF. The most r a d i a t i o n r e s i s t a n t p o l y s u l f o n e i n v e s t i g a t e d was Bp PSF, G(SO ) of 0.063. A l t h o u g h the s u l f o n e group i s n o t d i r e c t l y a t t a c h e d t o the b i p h e n y l group, t h e r e i s e v i d e n t l y a l a r g e p r o t e c t i v e e f f e c t e i t h e r through space or a l o n g the c h a i n . T h i s i s i n a c c o r d a n c e w i t h the s u b s t a n t i a l l y g r e a t e r r a d i a t i o n r e s i s t a n c e of b i p h e n y l , compared w i t h benzene as shown by G ( r a d i c a l ) v a l u e s of 0.045 and 0.2(12) r e s p e c t i v e l y . The t o t a l " a r o m a t i c " c o n t e n t of Bp PSF i s o n l y s l i g h t l y h i g h e r than f o r B i s - A PSF and t h u s does n o t a c c o u n t f o r the l a r g e i n c r e a s e i n r a d i a t i o n r e s i s t a n c e o b s e r v e d . One p o s s i b i l i t y i s t h a t the r a d i c a l c a t i o n s and a n i o n s formed immediately a f t e r i r r a d i a t i o n a r e s t a b i l i z e d t o a g r e a t e r e x t e n t i n the b i p h e n y l case than f o r a s i n g l e p h e n y l r i n g . The a r o m a t i c r i n g s i n the b i p h e n y l group a r e n e a r l y 90° o u t of the p l a n e of t h e m o l e c u l e , which s u g g e s t s t h a t t h e r e i s l i t t l e i n t e r a c t i o n between t h e s e r i n g s , f o r the n e u t r a l group. A f t e r i o n i z a t i o n o r e l e c t r o n c a p t u r e ( t o form the r a d i c a l c a t i o n and r a d i c a l a n i o n r e s p e c t i v e l y ) , the o r i e n t a t i o n of the r i n g s c o u l d be a l t e r e d , which would a l l o w g r e a t e r i n t e r a c t i o n and thus c h a r g e d e r e a l i z a t i o n . T h i s p r o p o s e d r e o r i e n t a t i o n c l e a r l y i s one e x p l a n a t i o n f o r the enhanced s t a b i l i t y , compared w i t h r a d i c a l c a t i o n s o r a n i o n s d e r i v e d from a r o m a t i c r i n g s such as found i n B i s - A PSF o r Hq PSF. G ( S 0 ) f o r Hq/Bp (50) PSF i s i n t e r m e d i a t e between G ( S 0 ) f o r the homopolymers. Thus, t h e r e i s no a d d i t i o n a l p r o t e c t i v e e f f e c t a n a l o g o u s t o the n o n - l i n e a r r e s p o n s e o f G(H ) as t h e mole f r a c t i o n of benzene i n c y c l o h e x a n e i s i n c r e a s e d (3,4;. This indicates that the s p a t i a l range of enhanced r a d i a t i o n p r o t e c t i o n a f f o r d e d by t h e b i p h e n y l group i s l i m i t e d . u l t i m a t e l y , i t i s the r e t e n t i o n of m e c h a n i c a l p r o p e r t i e s a f t e r i r r a d i a t i o n which w i l l d e t e r m i n e the s u i t a b i l i t y of a polymer f o r use i n a r a d i a t i o n e n v i r o n m e n t . S i n c e the p o t e n t i a l a p p l i c a t i o n s f o r t h i s c l a s s o f polymer r e q u i r e h i g h modulus and toughness o v e r 2

2

2


258


an extended dose range, the properties of most interest are Youngs modulus, ultimate s t r a i n and the fracture toughness. Youngs modulus increased s i g n i f i c a n t l y after a dose of 500 kGy, but increased only s l i g h t l y more at higher doses, as can be seen in Table IV. The increase i s attributed to the radiation

Table IV Influence of Irradiation on Mechanical Behavior Hq/BP(50) PSF


Bis-A PSF

Dose/kGy 0 500 1000 2000 4000

a

Modulus/MPa 1200 1660 1750 1600 1880

ultimate Elongation/% 110 80 33 20 8

Modulus/MPa

ultimate Elongation/% 74 100 70 60 51

1163 1650 1650 1750 1700

I r r a d i a t i o n conducted at 30°C under vacuum

induced network formation and i s consistent with observations with other systems (6,11). The modulus for Hq/Bp (50) PSF increases i n a similar manner, suggesting s i m i l a r i t y in the c r o s s l i n k i n g reactions of these two polymers. The mechanical property which i s most sensitive to r a d i a t i o n degradation i s the elongation at f a i l u r e . This invariably decreases regardless of whether chain s c i s s i o n or c r o s s l i n k i n g i s predominant. For Bis-A PSF, the elongation at f a i l u r e decreases rapidly from 110% i n i t i a l l y to 8% after a dose of 4000 kGy at ambient temperature as shown i n Table IV. This result i s i n remarkable agreement with the electron beam i r r a d i a t i o n of Bis-A PSF i n vacuum (6), which showed a reduction in the elongation at f a i l u r e from 110% i n i t i a l l y to 12% after a radiation dose of 3600 kGy. This i s evidence for l i t t l e dose rate dependency in the radiaJion degradation of Bis-A PSF, for dose rates up to 3600 kGyh for the f i l m thickness and cooling used in that study. For Hq/Bp(50) PSF, the decrease i n the elongation at f a i l u r e with i r r a d i a t i o n dose i s s i g n i f i c a n t l y less than for Bis-A PSF. This can be attributed to the increased radiation resistance afforded by the biphenyl moiety, as demonstrated from G(S0 ) measurements· The decrease i n the elongation at f a i l u r e suggested that the fracture toughness might also decrease after i r r a d i a t i o n . This was confirmed from the Κ measurements which showed a decrease from an i n i t i a l value of 2.0x10 Nm" ' to 1.7x10 Nm a f t e r 1000 kGy. The decrease i n Κ correlated with the decrease^ i n j e g s i l e elongation at f a i l u r e . A f i n a l value of 1.4x10 Nm a f t e r 4000 kGy was observed. 2

/



15.

LEWIS ET AL.

I

Figure 1.

Radiation-Resistant Poly (arylene ether sulfones)

I -100

I -90

259

I I I I I I -80 -70 -60 -50 -40 Temperature, °C Influence of Irradiation on $-Relaxation of Poly(Arylene Ether Sulfones) Bis-A polysulfone (Θ) unirradiated, (O) after 930 kGy and (·) after 4000 kGy.


260


Fracture toughness may correlate with the 3 relaxation temperature for the polymer. After irradiation, the 3 relaxation temperature increases with a corresponding broadening and decrease in intensity which can be seen in Figure 1. This result is consistent with the results of Hinkley et. al. (13^) who observed the same phenomenon for polyether sulfone irradiated with electron beam irradiation above Tg.


Conclusions This research demonstrates the utility of a well-defined set of polymers with carefully controlled structure for relating structure to radiation resistance. The presence of the isopropylidene group in the polymer apparently had little effect on the radiation resistance of the polymer, as determined from volatile product yields, contrary to initial expectations. G(CH^) was extremely small, indicating that isopropylidene bond scission is of a low probability. This was further confirmed from G(S02> measurements. Bp PSF was the most radiation resistant polysulfone studied. This is attributed to a stabilization of the radical cations and anions formed immediately after absorption of energy by the biphenyl group. The protective effect of this group apparently acts either intramolecularly or through space, since the principal radiation induced volatile product, sulfur dioxide, is derived from the sulfone group which is not adjacent to the biphenyl group. The overall aromatic content of Bp PSF is similar to Bis-A PSF and this difference is not significant enough to explain the enhanced radiation resistance of Bp PSF observed. The increase in the modulus for Bis A PSF and Hq/Bp PSF with irradiation indicated that crosslinking predominated for both polymers and that the crosslink structures were probably basically similar. Hq/Bp(50) PSF was considerably more radiation resistant than Bis-A PSF, as shown by the rate of decrease in the elongation at failure. For both polymers, there was an initial rapid decrease in the elongation at failure followed by a slower decrease. This effect was also demonstrated by the variation in the fracture toughness (KIC) with irradiation for Bis-A PSF. This work with cobalt-60 gamma radiation complements earlier studies of these materials using high dose rate electron beam irradiation (6). Acknowledgment The authors appreciate the support of the NASA Langley Research Center for portions of this research. Literature Cited 1. 2. 3. 4.

Brown, J. R.; O'Donnell, J. H., J. Polym. Sci., Polym Lett., 1970, 8, 121. Brown, J. R.; O'Donnell, J. H., J. Appl. Poly. Sci., 1975, 19, 405. Ho, S. K.; Freeman, G. R., J. Phys. Chem., 1964, 68, 2189. Gordon, S.; Van Dyken, A. R.; Doumani, T. F., J. Phys. Chem., 1958, 62, 20.


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Radiation-Resistant Poly (arylene ether sulfones) 261


5.

Viswanathan, R.; Johnson, B. C.; and McGrath, J. E.; Polymer, 1984, 25, 1827. 6. Hedrick, J. L.; Mohanty, D. K.; Johnson, B. C.; Viswanathan, R.; Hinkley, J. A.; McGrath, J. E., J. Polym. Sci.; Chem. Ed., 1986, 23, 287. 7. Bowmer, T. N.; O'Donnell, J. H., Polymer, 1977, 18, 1032. 8. Bowmer, T. N. Ph.D. Thesis, University of Queensland, Australia, 1979. 9. O'Donnell, J. H.; Sangster, D. F., Principles of Radiation Chemistry, 1970 Edward Arnold, London. 10. Lewis, D. A. Ph.D. Thesis, University of Queensland, Australia, 1988. 11. Sasuga, T.; Hayakawa, N.; Yoshida, K.; Hagiwara, Μ., Polymer, 1985, 26, 1039. 12. Ayscough, P. Β., Electron Spin Resonance in Chemistry, 1967 Butler and Tanner, London, 343. 13. Hinkley, J. A.; J. Polym. Sci.; Polym. Lett. Ed., 1984, 22, 497. RECEIVED July 29, 1988


The Effects of Radiation on High-Technology Polymers - American

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