Torsional Pendulum Analysis of the Influence of ... - ACS Publications

26 Torsional Pendulum Analysis of the Influence of Molecular Structure on the Cure and Transitions of Polyphthalocyanines

Downloaded by CORNELL UNIV on May 23, 2017 | http://pubs.acs.org Publication Date: August 28, 1980 | doi: 10.1021/bk-1980-0132.ch026

JOHN K. GILLHAM P o l y m e r M a t e r i a l s P r o g r a m , D e p a r t m e n t of C h e m i c a l E n g i n e e r i n g , P r i n c e t o n U n i v e r s i t y , P r i n c e t o n , NJ 08544

T h i s r e p o r t f o l l o w s up an earlier study (1) i n which an automated t o r s i o n pendulum was used t o i n v e s t i g a t e the t r a n s f o r mation (cure) o f a "C diamide phthalocyanine" r e s i n monomer t o thermoset polymer u s i n g supported specimens [ t o r s i o n a l b r a i d a n a l y s i s , TBA, (2,3). The o v e r a l l chemical r e a c t i o n f o r p o l y m e r i z a t i o n o f the C diamide monomer is shown in F i g u r e 1. The bis aromatic orthodinitrile monomer r e a c t s t o form a network o f C diamide segments l i n k e d by t e t r a f u n c t i o n a l phthalocyanine branching sites. In general thermosetting p o l y m e r i z a t i o n proceeds from liquid monomer (with a g l a s s t r a n s i t i o n temperature below the initial m e l t i n g temperature o f the pure monomer), through g e l a t i o n (as branched molecules o f infinite molecular weight form), through the rubbery s t a t e (as network molecules form), and finally (when the temperature o f r e a c t i o n is below the maximum a t t a i n a b l e g l a s s t r a n s i t i o n temperature) t o vitrification. F a b r i c a t i o n can i n v o l v e use o f t r a c t a b l e prepolymer ( i . e . n o n - g e l l e d oligomer) f o r molding in to i n t r a c t a b l e product. Cure was examined d i r e c t l y from isothermal p l o t s a t d i f f e r e n t temperatures, and a l s o from t r a n s i t i o n temperatures, which were obtained from thermomechanical p l o t s o f i n t e r m i t t e n t l y cooled specimens, versus time o f isothermal cure. In the p r e s e n t work the i n f l u e n c e o f molecular s t r u c t u r e on the t r a n s i t i o n s , p a r t i c u l a r l y the g l a s s t r a n s i t i o n (Tg) and a cryogenic t r a n s i t i o n ( T ) a s s o c i a t e d with the f l e x i b l e molecular segment o f the monomer and of the r e s u l t i n g network, has been i n v e s t i g a t e d using a n a l y t i c a l l y pure monomers designated Cg-methyl, C I Q , and C 2 2 diamide phthalocyanine r e s i n monomers. A p r e l i m i n a r y r e p o r t has been publ i s h e d (4) . 10

10

10

situ

s e c

0-8412-0567-l/80/47-132-349$05.00/0 © 1980 A m e r i c a n C h e m i c a l Society

May; Resins for Aerospace ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


RESINS FOR

MONOMERS

N

C

^ N H C O ( C H

POLYMERS

2

)

8

~ H0C^ R

1

C O N H - 0 -

C

HEAT

N

ιK D O " "

N

C

ΛΚ N

R

Ι

ft-cf P=N

~R~

Figure 1.

S

-fNHCOtCHgîeCONHf

Overall chemical reaction:

C

10


AEROSPACE

26.

GiLLHAM

Torsion

Pendulum

Analyses

351

Experimental Monomers. The monomers, which d i f f e r i n the l i n k a g e connecting the two aromatic ends, were obtained from the Naval Research Laboratory, Washington, D.C. The chemistry o f t h e i r s y n t h e s i s and p o l y m e r i z a t i o n has been reported (_5). The monomers and t h e i r designa t i o n s were: "C -methyl diamide" i . e . , Ν,Ν'-bis(3,4-dicyanophenyl) 3-methyIhexanediamide, mp 203-206°C. "C diamide" i . e . , Ν,Ν'-bis (3,4-dicyanophenyl) decanediamide, mp 185-189°C. "C diamide" i . e . , Ν,Ν'-bis(3,4-dicyanophenyl) tetradecanediamide, mp 163-165°C. " C 2 2 diamide" i . e . , Ν,Ν'-bis(3,4-dicyanophenyl) docosanediamide, mp 144-147°C.


6

1 0

li+

T o r s i o n Pendulum. An automated, i n t e r m i t t e n t l y a c t i v a t e d , f r e e l y v i b r a t i n g t o r s i o n pendulum o p e r a t i n g a t about 1 Hz (2^,_3) was used f o r a l l experiments. (A v e r s i o n o f the instrumental system i s a v a i l a b l e from P l a s t i c s A n a l y s i s Instruments, Inc., P.O. Box 408, P r i n c e t o n , NJ.) Each specimen was made by d i p p i n g a g l a s s b r a i d i n t o a s l u r r y o f monomer i n e t h y l a l c o h o l . A f t e r mounting a specimen i n the apparatus a t room temperature (RT) the temperature was r a i s e d to the isothermal cure temperature a t 5°C/min. Cure was monitored both continuously a t the i s o t h e r m a l temperature and, i n a separate experiment, by i n t e r m i t t e n t l y c o o l i n g and then h e a t i n g back (gen e r a l l y a t 1.5°C/minute) t o the isothermal cure temperature t o r e c o r d the thermomechanical s p e c t r a (which were used t o a s s i g n t r a n s i t i o n temperatures). A l l experiments were performed i n dry helium. Each specimen consumed about 20 mg o f monomer. The t o r s i o n pendulum p l o t s d i s p l a y the r e l a t i v e r i g i d i t y (1/P , where Ρ i s the p e r i o d i n seconds o f a f r e e l y damped wave) and l o g a r i t h m i c decrement Δ(= In A-j/Ai+i, where Αχ i s the ampli tude o f the ith o s c i l l a t i o n o f a wave) versus temperature (mV from an i r o n - c o n s t a n t a n thermocouple) o r time. These mechanical param e t e r s r e l a t e d i r e c t l y to dynamic mechanical t e s t i n g i n t h a t the r e l a t i v e r i g i d i t y i s d i r e c t l y p r o p o r t i o n a l t o the in-phase shear modulus (G ) and Δ - TTtanO, where δ i s the phase angle between c y c l i c s t r e s s and s t r a i n . T r a n s i t i o n temperatures were assigned using the peaks o f the l o g a r i t h m i c decrement; i n t e n s i t i e s o f t r a n s i t i o n s were assigned u s i n g values o f Δ. 2

1


352

RESINS FOR

Results and

AEROSPACE

Discussion

An isothermal temperature of 250°C was s e l e c t e d f o r studying 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 s i n c e higher temperatures l e a d to weak g l a s s t r a n s i t i o n s and t o degradation. The immediate d i s cussion emphasizes Tg which was i d e n t i f i e d as the most dominant l o s s peak a t high temperature i n a thermomechanical spectrum. Other t r a n s i t i o n s are considered more completely l a t e r . The g l a s s t r a n s i t i o n temperatures versus time of cure a t 250°C are i n c l u d e d i n Tables I - I V and i n Figures 2-5. The i n i t i a l Tg f o r a l l of the monomers was l e s s than 100°C. On heating, the g l a s s t r a n s i t i o n temperature i n c r e a s e d more r a p i d l y and, a f t e r about 5 hours, reached a higher l i m i t i n g temperature (designated 2 5Q g«>) the s h o r t e r the l e n g t h of the i n t e r - a r o m a t i c molecular l i n k a g e s . Values f o r 250 g°° (see Table V) were: C -methyl > 244°C, C I Q ^ 202°C, Cm * 185°C, and C 2 ^ 157°C. A p l o t o f 250 g*> versus the number of i n t e r - a r o m a t i c C atoms, which i s an index of segmental molecular f l e x i b i l i t y , i s shown i n F i g u r e 6. As the temperature of Tg i n c r e a s e d with extent o f cure, the i n t e n s i t y o f Tg decreased for a l l four m a t e r i a l s (Tables I to IV). T h i s could l e a d to an u n c e r t a i n t y i n d e s i g n a t i n g Tg (see below). P l o t s o f isothermal cure f o r 5 hours a t 250°C f o r the four monomers are shown i n F i g u r e s 7A, 7B, 7C, and 7D. The c o r r e s ponding subsequent thermomechanical p l o t s (250°C -* -190°C) are shown i n Figures 8A, 8B, 8C and 8D. Comparison o f each p a i r o f isothermal and thermomechanical p l o t s shows t h a t two l o s s p r o cesses (peaks or shoulders) occur i s o t h e r m a l l y n e i t h e r of which i s assigned as the g l a s s t r a n s i t i o n ( v i t r i f i c a t i o n ) , which i s revealed i n the corresponding thermomechanical p l o t s a t lower temperatures than the isothermal cure temperature. The f i r s t i s o thermal l o s s peak probably occurs a t an i s o v i s c o u s l e v e l and has been used t o measure g e l a t i o n times (1/2.* 3j ; the second isothermal "peak" presumably corresponds to the T££ (or Τ > Tg) r e l a x a t i o n (1,6) which occurs immediately above Tg i n temperature scans o f thermoplastic m a t e r i a l (see l a t e r ) . The procedure f o r a s s i g n i n g Tg i s more c o n v i n c i n g l y demon s t r a t e d than i n F i g u r e s 7A-7D and Figures 8A-8D by comparing the p l o t o f isothermal cure a t 220°C (Figure 9) and the subsequent thermomechanical p l o t (Figure 10) o f the Cji+ m a t e r i a l : there can be l i t t l e doubt i n t h i s case t h a t the intense r e l a x a t i o n below the temperature o f isothermal cure i s Tg. V i t r i f i c a t i o n was not observed as a t h i r d process on isothermal cure f o r the four mater i a l s s i n c e the temperatures (250°C, Figures 7A to 7D and 220°C, F i g u r e 9) were above the maximum Tg a t t a i n e d i n the time s c a l e of the experiments. In the absence o f thermal degradation f u l l cure would be expected t o l e a d t o a network o f short linkages ( i . e . high c r o s s l i n k density) which would give r i s e only to a weak g l a s s t r a n s i t i o n perhaps b e t t e r c h a r a c t e r i z e d as a secondary t r a n s i t i o n . I f i s o t h e r m a l cure occurs a t temperatures j u s t below the g l a s s t r a n s i t i o n temperature o f the f u l l y cured m a t e r i a l , the l o s s peak a s s o c i a t e d with the r i s i n g g l a s s t r a n s i t i o n temperature ( i . e .


T

T

6

T

2


26.

GiLLHAM

Torsion

TABLE I . C _ 6

C H 3

1 2 3 4 5 6 7 8 9 10 11 12 13 14

5 5 23 23 41 41 83 83 133 133 230 230 545

TABLE I I .

C

1 0

:

353

Analyses

Transitions

Plot No.

Time a t 250°C Min. Downloaded by CORNELL UNIV on May 23, 2017 | http://pubs.acs.org Publication Date: August 28, 1980 | doi: 10.1021/bk-1980-0132.ch026

:

Pendulum

(>RT) Versus Cure Time a t 250°C. TRANSITIONS Τ > Tg Tg (Δ) °C °C

ΔΤ/ât - or +

+

-+

92 92 138 139 186 185 212 213 226 222 233 231 244

+

-+ -+ + -+

Transitions

(0.964) (0.966) (0.274) (0.267) (0.147) (0.141) (0.105) (0.0986) (0.0829) (0.0786) (0.0646) (0.0605) (0.0441)

111 110 246 223 >250

(>RT) Versus Cure Time a t 250°C. TRANSITIONS

Time a t 250°C Min. 10 10 28 28 46 46 94 131 269 635

Plot No. 1 2 3 4 5 6 8 9 10 11

ΔΤ/ât - or + —

+ + + -/+ -/+ -/+ -/+

Tg (Δ) °C 60.5 60 71 71 99.5 99 165.5 187.5 199 202.5

(2.587) (2.648) (1.801) (1.782) (0.818) (0.804) (0.362) (0.283) (0.208) (0.139)

Τ > Tg 81.5 79.5 106 106.5 183.5 182


354

RESINS


TABLE I I I .

Cmz

Time a t 250°C Min. 0 5 5 5 5 5 23 23 33 33 66 99 99 465 465 1005 1005 1695 1695 2355

Transitions Plot No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

ΔΤ/At - or +

FOR

AEROSPACE

(> RT) Versus Cure Time a t 250°C. TRANSITIONS Tg (Δ) Τ > Tg (Τ· > Tg) °C °C

+

-+ -+ +

-+ + +

-+ -+ -+ -

(2.218) 49 (2.222) 49 (1.832) 50 50. 5(1.829) (2.499) 51 (1.414) 64 (1.404) 65 (0.551) 100 (0.534) 99 (0.334) 150 (0.257) 168 (0.250) 169 (0.137) 183 (0.132) 185 (0.100) 176 175 (0.0986) 163 (0.0840) (0.0830) 161 (0.0784) 152

70 * 75 * * 132 131 202 198

(^ 86) (VL02)

(^204) (^222)

Plots display multiple melting/crystallization transitions (e.g. see F i g u r e 11 f o r P l o t No. 5 ) . Adjacent p l o t s obtained on c o o l i n g ( i . e . 2,4,7) d i s p l a y amorphous behavior with Τ > Tg and T* > Tg r e l a x a t i o n s .


26.

GiLLHAM

Torsion

TABLE IV.

-22·

Transitions

355

Analyses

(> RT) Versus Cure Time a t 250°C. TRANSITIONS

Time a t 250°C Min.


Pendulum

Plot No.

ΔΤ/At - or + _

Tg (Δ) °C 87(?) 90 58 60 71 71 108 111 128 130 145 147 156 157 151.5 153 148

(0.243) (0.217) (0.538) (0.535) (0.388) (0.382) (0.256) (0.250) (0.202) (0.200) (0.143) (0.145) (0.101) (0.100) (0.0789) (0.0660) (0.0685)

Τ > Tg (T» > Tg)[Other] °C [T 93] [T 134] 124 (219) 129 [ 1 4 1 A 2 3 1 ] 184 (^254) 183 233 ^226

5 5 23 23 41 41

2 3 4 5 6 7

89 89 131 131 296 296 824 2432 2432 5048 5048

8 9 10 11 12 13 14 15 16 17 18

TABLE V.

2 5 0 g o o Versus E f f e c t i v e Number o f Inter-Aromatic Carbon Atoms.

+

-+ + + -+ -+ -+ +

I>50]

[52A88] [^48]

T

Polymer

C

c r y

m

6-CH

3

E f f e c t i v e Number of Carbon Atoms* 5.5

_ _ . T (°C) 250 g°° > 244

C

1 0

10

^ 202

C

1Î+

14

^ 185

C2

22

^ 157

2

E f f e c t i v e number o f carbon atoms/inter-aromatic segment i s taken as the number o f unbranched C atoms between the amide Ν atoms i n the monomer, except f o r C 6 - C H 3 which i s assigned 0.5 l e s s than 6 because o f the s t i f f e n i n g e f f e c t o f a branched C.


RESINS F O R A E R O S P A C E


356

Figure 2. C -CH : transitions (> RT) vs. cure time at 250°C s

6

Figure 3.

C : transitions (> RT) vs. cure time at 250°C

Figure 4.

C : transitions (> RT) vs. cure time at 250°C

10

u



GiLLHAM

Torsion

Pendulum

200

0

Analyses

400

600

800

1000

TIME,( MINUTES )

Figure 5.

0

C : transitions (> RT) vs. cure time at 22

4

8

12

16

20

250°C

24

EFFECTIVE NUMBER OF INTER-AROMATIC CARBON ATOMS

Figure 6.

i S 0

T v s . effective number of interaromatic carbon atoms



Ί

1

1

Γ

I

I

L


LOG-

I

1

J

L

I

TIME,(SEC.)

Figure 7A.

Isothermal cure (250°C/5 hr): C -CH 6

S

TEMPERATURE C O ure 8A.

Thermomechanical spectra (220°

-» —190°C)

after 250°C/5


hr cure:

GiLLHAM

Torsion Pendulum

Analyses τ


oh

ΙΟ

10*

1

ΙΟ

ΙΟ

3

ΙΟ

4

5

TIME,(SEC.)

Figure 7B.

-190

-136

-85

Isothermal cure (250°C/5

-41

0

39

77

hr): C-

114

150

186

TEMPERATURE ( C) e

Figure 8B.

Thermomechanical spectra (220° -> -190°C)

after 250°C/5

hr cure:


360


RESINS FOR AEROSPACE

Figure 7C.


hr): C-

TEMPERATURE (°C)

Figure 8C.

Thermomechanical spectra (220°

-> -190°C)

after 250°C/5

hr cure:


GiLLHAM

Torsion Pendulum

Analyses

τ

1

1

1

1

Γ


oh

ίο

1

Figure 7D.

to io TIME,(SEC.) 2

3


io

4

io

5

hr): C,

TEMPERATURE ( C) e

Figure 8D.

Thermomechanical spectra (220° CM

-> -190°C)

after 250°C/5

hr cure:




362

Figure 10. Thermomechanical spectra (220° -> 45°C, Δ Τ / A t < after 220°C/16.5 hr cure (same specimen as for Figure 9): C

1.5°C/min) u


26.

GiLLHAM

Torsion

Pendulum

Analyses

363

v i t r i f i c a t i o n ) would be observed i s o t h e r m a l l y as a prolonged (be cause the r a t e o f r e a c t i o n would be c o n t r o l l e d by the low concen t r a t i o n o f r e a c t i v e groups a t l a t e stages o f chemical conversion) and weak process. I t does appear t h a t o f the four m a t e r i a l s the maximum g l a s s t r a n s i t i o n temperature may be above 250°C only f o r the Cg-methyl m a t e r i a l ; comparison o f Figures 7A and 8A shows t h a t the maximum Tg a t t a i n e d ( a f t e r 5 hours a t 250°C) i s c l o s e t o 250°C. The thermomechanical p l o t s (Figures 8Ά, 8B, 8C and 8D) f o r the four m a t e r i a l s obtained a f t e r c u r i n g a t 250°C f o r 5 hours d i s p l a y two t r a n s i t i o n s below Tg. Numerical values a r e given i n Table V I . The cryogenic, more intense t r a n s i t i o n , designated T , i s a s c r i b e d (1^,4^,7) t o motion o f the f l e x i b l e i n t e r - a r o m a t i c seg ments. As a n t i c i p a t e d , the more f l e x i b l e the segment the more intense the cryogenic mechanical l o s s peak: the i n t e n s i t y there f o r e increases i n the order Cg-methyl < C ^ Q < C m < C22- The l e a s t f l e x i b l e segment, i n the Cg-methyl m a t e r i a l , i s a l s o respon s i b l e f o r i t s l o s s peak being a t a higher temperature (-98°C) than f o r i t s higher homologues (^ -140°C). The weaker T * transition between Tg and T a l s o occurs a t h i g h e r temperatures the lower the segmental f l e x i b i l i t y ; however i t s i n t e n s i t y increases r e l a t i v e t o the background and r e l a t i v e t o t h a t o f i t s T relaxation i n the order Cg-methyl > CIQ > C > C 2- The o r i g i n o f the T g ^ r e l a x a t i o n i s unknown. J u s t as two r e l a x a t i o n s occur p r i o r t o v i t r i f i c a t i o n i n i s o thermal cure, so two r e l a x a t i o n s occur above Tg (designated T > Tg and Τ > Tg) i n TBA thermomechanical p l o t s o f low molecular weight m a t e r i a l (1,6_). They move q u i c k l y t o higher temperatures with extent o f cure, as i n d i c a t e d i n F i g u r e s 2 t o 5 f o r Τ > Tg and Figures 4 and 5 f o r Τ > Tg, and r e v e a l e d i n the corresponding thermomechanical p l o t s (not shown here, but see reference JL f o r the CIQ diamide). They should be o f importance t o p r o c e s s i n g s i n c e they occur above Tg. In the course o f t h i s work high r e s o l u t i o n thermomechanical s p e c t r a o f low molecular weight m a t e r i a l were obtained, i n c l u d i n g the f o l l o w i n g example. M e l t i n g o f the C m monomer (RT -> 250°C, ΔΤ/At 5°C/min; 250°C/5 min) and subsequent c o o l i n g (ΔΤ/At 200°C, ΔΤ/At 0.5°C/min) o f which i s shown i n F i g u r e 11 (see a l s o footnote t o Table I I I ) . I n t e r p r e t a t i o n i n terms o f the sequence o f t r a n s i t i o n s (designated by the l o s s peaks) f o l l o w s : The r i g i d i t y o f the g l a s s decreases through Tg (50.5°C), increases as a consequence o f c r y s t a l l i z a t i o n (68°C) and decreases through a s e r i e s o f w e l l - d e f i n e d melting steps (132°C, 143°C, 152°C and 163°C). The reported melting range was 163-165°C (5). The thermomechanical s p e c t r a on h e a t i n g were r e p r o d u c i b l e f o r a f i x e d c o o l i n g rate from the melt. By changing the c o o l i n g condi t i o n s from the melt i n the p r e h i s t o r y , the r e l a t i v e i n t e n s i t i e s o f the t r a n s i t i o n s c o u l d be changed s y s t e m a t i c a l l y . M u l t i p l e melting peaks have been observed on phthalocyanine prepreg m a t e r i a l u s i n g DSC (8).


s e c

s e c

s e c

s e c

1

1Lf

2

1

1


364

RESINS

TABLE V I .


6-CH

C

T (A) 2

3

4

3

C

lk

C

2 2

Figure 11. 0.5°C/min)

T

g

1 0

AEROSPACE

Polyphthalocyanines: T r a n s i t i o n s (°C) A f t e r 5 Hour Cure a t 250°C.

Polymer C

FOR

(0.180)

19

f s e c

(Δ)

(0.0443)

T

g e c

(Δ)

-98 (0.0415)

194

(0.136)

3

(0.0342)

-145 (0.0858)

178

(0.160)

8

(0.0427)

-140 (0.155)

137

(0.234)

1

(0.0459)

-139 (0.229)

C monomer: thermomechanical spectra ( R T - » 200° C, Δ Τ / Δ ί < after melting (250°C/5 min) and subsequent cooling (ΔΤ/Δί < 0.5° C/min) n


26.

GiLLHAM

Torsion

Pendulum

Analyses

365

Summary An automated t o r s i o n pendulum has been used to study s t r u c ture/property r e l a t i o n s h i p s o f four phthalocyanine r e s i n s d e s i g nated Cg-CH , C | Q , Cm. and 0 2 · The d e s i g n a t i o n r e f l e c t s the d i f f e r e n t segments between the aromatic n u c l e i o f the monomers and of the r e s u l t i n g molecular networks. Cure a t 250°C r e s u l t e d i n l i m i t i n g g l a s s t r a n s i t i o n temperatures, 2 50 g°°' which decreased as the segmental length i n c r e a s e d : the values were Cg-methyl > 244°C, C ^ 202°C, C ^ 185°C and C 2 ^ 157°C. A f t e r a standard cure o f 250°C/5 h r . the thermomechanical s p e c t r a r e v e a l e d two t r a n s i t i o n s below Tg. That a t cryogenic temperatures (designated T ) was a t t r i b u t e d t o motions o f the i n t e r - a r o m a t i c molecular segments? the g r e a t e r the f l e x i b i l i t y o f the segments, the lower the temperature and the more i n t e n s e the T relaxation. The r e l a x a t i o n between Tg and T (designated T g ^ ) a l s o o c c u r r e d at lower temperature the g r e a t e r the segmental f l e x i b i l i t y but with d e c r e a s i n g i n t e n s i t y ( r e l a t i v e t o the background). Two other r e l a x a t i o n s o c c u r r i n g above Tg moved t o h i g h e r temperatures more r a p i d l y than Tg on cure: these bear on the p r o c e s s i b i l i t y of the m a t e r i a l s i n the e a r l y stages o f cure. 3

2

T


1 0

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2

s e c

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1

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Acknowledgment A p p r e c i a t i o n i s extended t o Dr. W. D. Bascom and Dr. J . R. G r i f f i t h o f the Naval Research Laboratory f o r p r o v i d i n g samples o f the f o u r monomers and f o r t h e i r t e c h n i c a l i n t e r a c t i o n s .

Literature Cited 1. 2. 3. 4. 5.

6. 7.

8.

Gillham, J. Κ., Polym. Eng. and S c i . , 19(4), 319 (1979). Gillham, J. Κ., A.I.Ch.E. J . , 20(6), 1066 (1974). G i l l h a m , J. Κ., Polym. Eng. and S c i . , 19 (10), 676 (1979). Gillham, J. Κ., Amer. Chem. Soc., P r e p r i n t s , Div. Organic Coatings and P l a s t i c s Chem., 40, 866 (1979). Griffith, J . R. and O'Rear, J . G., in High Performance Com p o s i t e s and Adhesives f o r V/STOL Aircraft, NRL Memorandum Report 3721, pp 15-20 (Ed. Bascom, W. D., and Lockhart, L. Β., Jr.), Naval Research Laboratory, Washington, D.C., Feb. 1978. Gillham, J . K., Benci, J. Α., and Boyer, R. F., Polym. Eng. and S c i . , 16(5), 357 (1976). Bascom, W. D., C o t t i n g t o n , R. L., B i t n e r , J . L., Hunston, D. L., and Oroshnik, J . , i n High Performance Composites and Adhesives f o r V/STOL Aircraft, NRL Memorandum Report 3721, pp 23-35 (Ed. Bascom, W. D., and Lockhart, L.B., J r . ) , Naval Research Laboratory, Washington, D.C., Feb. 1978. Griffith, J . R., p r i v a t e communication (1978).

RECEIVED February 15, 1980.


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