Modification of Polymers - American Chemical Society

30 Structure and Property Modification of m-Carborane

Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 24, 2018 | https://pubs.acs.org Publication Date: June 10, 1980 | doi: 10.1021/bk-1980-0121.ch030

Siloxanes EDWARD N. PETERS Union Carbide Corporation, One River Road, Bound Brook, NJ 08805

Carborane-siloxanes are a family of polymers which have the linear structure, I,

I where R and R' can be methyl or fluoroalkyl, and in addition R' can be phenyl. The interest in carborane-siloxanes centers around the need for new polymers having enhanced flame resistance, and greater thermal and oxidative stability (1). Indeed the incorporation of the m-carborane moiety into the siloxane backbone has resulted in significant enhancement of properties. Several approaches are available for modifying polymer properties in order to maximize the performance of a polymeric system for a particular end use. These methods include polymer backbone modification, polymer blends, grafting, and the use of additives such as reinforcements, cross-linking agents, stabilizers, plasticizers, etc. The properties of carborane-siloxane polymers can be modified and optimized through a combination of structural changes and the use of supplementary agents. The work from several laboratories including Olin Corporation, Princeton University, and Union Carbide Corporation will be reviewed in this chapter. Backbone Modification Different structures of carbone-siloxane polymers are obtainable via several synthetic routes which have been developed. 0-8412-0540-X/80/47-121-449$05.00/0 © 1980 American Chemical Society Carraher and Tsuda; Modification of Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

450

MODIFICATION OF POLYMERS

P o l y m e r s ( I ) where η i s 3 a n d 5 c a n b e p r e p a r e d b y h y d r o l y s i s - c o n d e n s a t i o n o f a c a r b o r a n e - b a s e d s i l o x a n e a s shown i n e q u a t i o n 1 (2)· R'

R

R

R'

ι

Υ Ί

1

Y YJ Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 24, 2018 | https://pubs.acs.org Publication Date: June 10, 1980 | doi: 10.1021/bk-1980-0121.ch030

CH

"T"CH

3

CH

3

H

?.°

- I

(1)

C H ~T~

3

3

P o l y m e r s (_I) where η i s 4, 5, a n d 6 a r e p r e p a r e d b y t h e c o h y d r o l y s i s - c o n d e n s a t i o n o f a b i s ( c h l o r o d i s i l o x y l ) c a r b o r a n e and a d i c h l o r o s i l i c o n c o m p o u n d w h i c h a p p e a r i n e q u a t i o n 2 (_2) · R'

R

1

R

1

1

R'

R'

1

R'

I

/

I

\

1

λ

Cl-Si-O-SiCB H CSi-O-Si-Cl + Cl-Si-fO-Si-4-Cl 1 0

I I CH

I I CH

3

HoO

1 0

CH

3

3

CH

CH

3

I_

(2)

I /n-4 CH

3

3

The p o l y m e r where η i s 2 c a n b e p r e p a r e d a c c o r d i n g t o e q u a t i o n 3 i n which a b i s ( h y d r o x y s i l y l ) c a r b o r a n e i s reacted w i t h a b i s u r e i d o s i l a n e where X i s a n N - p h e n y l - N ' - t e t r a m e t h y l e n e u r e i d o group (3^) · R

R

I

I

R'

I

1

HO-SiCB H CSi-OH + X-Si-X 1 0

1 0

I

I

CH

CH

3

CH

3

E q u a t i o n 4 shows t h e f e r r i c p o l y m e r where η i s 1 ( 4 ) . R

R

I

3

chloride

R

catalyzed

I

I

C l - S i C B H C S i - C l + CH O-SiCB H CSi-OCH

I CH

1 0

3

1 0

I

Transition

1 0

I CH

3

3

CH

synthesis of

R

I 1 0

(3)

I

3

FeCla_ — ^ - M »» 1 X

3

(4)

I CH

3

Temperatures

The two m a i n t r a n s i t i o n s i n p o l y m e r s a r e t h e g l a s s - r u b b e r t r a n s i t i o n (Tg) and t h e c r y s t a l l i n e m e l t i n g p o i n t (Tm). The Tg i s t h e most i m p o r t a n t b a s i c p a r a m e t e r o f a n amorphous p o l y m e r b e c a u s e i t d e t e r m i n e s w h e t h e r t h e m a t e r i a l w i l l be a h a r d s o l i d o r an e l a s t o m e r a t s p e c i f i c u s e t e m p e r a t u r e r a n g e s and a t what temperature i t s b e h a v i o r p a t t e r n changes.

Carraher and Tsuda; Modification of Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

m-Carborane

30. PETERS

Siloxanes

451

Physical t r a n s i t i o n s f o r a series of l i n e a r carboranes i l o x a n e p o l y m e r s , I_, h a v e b e e n examined and t h e d a t a a p p e a r i n Table I .

TABLE I T r a n s i t i o n s and S t a b i l i t y o f C a r b o r a n e - S i l o x a n e s


R 1 2 2

CH CH CH

2

CHo j

2

CH

R' —

3

CH C H /CH (33) I C H (67) f C H (67) I C H (33) CH CH CH

3

3

3

6

5

3

6

3

3

CH CH CH CH CH CH CH CH 3

3

3

3

2

CH CF 2

—

3

CH CH CF CH CH CH CF CH CH CF

3

2

2

2

CH CF CH CF CH CF 2

3

2

3

2

3

25 -42 -12

260 90 A

20% 32% -5%

-22

A

-5%

-27

A

-5%

-68 -75 -88 28 -29 -12 -3 -15

A A A A A A A A

45% 48% 60%

5

3

3

Wt. L o s s b y 700°C

Tm, °C

5

6

3 4 5 1 2 2 2 3

T g , °C

2

2

3

2

2

3

2

2

3

3

—

25% 59% 69% 78%

A = Absent For t h e homologous s e r i e s o f carborane-dimethylsiloxanes ( I , R = R'= C H , η = 1 t h r o u g h 5 ) , t h e g l a s s t r a n s i t i o n t e m p e r a t u r e d e c r e a s e s w i t h i n c r e a s i n g s i l o x a n e c o n t e n t ( i . e . , g r e a t e r n) (5) · When η i s 1 o r 2 t h e p o l y m e r s h a v e a c r y s t a l l i n e m e l t i n g point. T h i s c r y s t a l l i n e phase a d v e r s e l y affects elastomeric properties. I n t h e c a s e where η = 2, t h i s c r y s t a l l i n i t y c a n b e e l i m i n a t e d by t h e i n c o r p o r a t i o n o f p h e n y l groups on t h e polymer b a c k b o n e ( R ' = C5H5). Thus, p h e n y l m o d i f i c a t i o n r e s u l t s i n a c o m p l e t e l y amorphous s y s t e m ; h o w e v e r , t h e Tg h a s r i s e n f r o m -42° t o -12°C. P a r t i a l p h e n y l m o d i f i c a t i o n (R' - C H / C H [67/33]) p r o d u c e s a n amorphous p o l y m e r w i t h a l o w Tg (-37°C) ( 6 ) . P o l y m e r s where η = 3,4, and 5 a r e amorphous w i t h d e c r e a s i n g Tg's o f - 6 8 ° , -75°, and -88°C, r e s p e c t i v e l y . The t r i f l u o r o p r o p y l m o d i f i e d p o l y m e r s a r e amorphous and e x i b i t d e c r e a s i n g Tg w i t h i n c r e a s i n g η and i n c r e a s i n g Tg w i t h i n c r e a s i n g C H C H C F c o n t e n t (J7> 8.)· A l i n e a r r e l a t i o n s h i p was o b t a i n e d f o r t h e homologous s e r i e s of carborane-dimethylsiloxanes and carborane-methyltrifluorop r o p y l s i l o x a n e s b y c o n s i d e r i n g t h e i r s t r u c t u r e s t o be an a l t e r n a t i n g copolymer of -(0-SiR -^ and -£CBiQHi0CSiR }- l i n k a g e s and by p l o t t i n g w e i g h t f r a c t i o n o f -£CBiQHi0CSiR -)- v e r s u s 1/Tg a s shown i n F i g u r e 1 ( 1 , _5). 3

3

2

2

2

6

5

3

2

n

2



452


I

I

I

I

0

0.1

0.2

0.3

I

0.4

I

I

0.5

0.6

1

1

1

0./

0.8

0.9

1 1.0

WEIGHT FRACTION -SiR CB H C2

Figure 1.

10

10

Correlation of glass transition temperatures

Thermal S t a b i l i t y One of the unique p r o p e r t i e s of carborane-siloxane polymers i s t h e i r o u t s t a n d i n g thermal s t a b i l i t y . Thermogravimetric analyses i n an i n e r t atmosphere r e v e a l that r a p i d weight l o s s does not occur u n t i l above 400°C. For the homologous s e r i e s of carborane-dimethylsiloxanes the s t a b i l i t y of the polymers i n c r e a s e s with decreasing s i l o x a n e content per repeat u n i t (5, 9). The t o t a l weight l o s t by 700°C appear i n Table I. A corr e l a t i o n of weight l o s s as a f u n c t i o n of s i l o x a n e l i n k a g e s per repeat u n i t i s shown i n F i g u r e 2. The phenyl modified polymers show a s i g n i f i c a n t decrease i n weight l o s s compared to t h e i r a l l methyl analog (6)· In a study of the thermal breakdown of phenyl s u b s t i t u t e d carborane-siloxane polymers, i t has been reported that the presence of phenyl groups i n carborane-siloxanes leads to c r o s s - l i n k i n g and l e s s l o s s of weight 09)· The p r e s e n c e of t r i f l u o r o p r o p y l groups on the polymer backbone leads to an i n c r e a s e i n weight l o s s (7^, 8). Thus, by modifying the polymer backbone the s t a b i l i t y and lower use temperature can be v a r i e d .


30.

PETERS

m-Carborane

453

Siloxanes


ioh

1

2

3

4

5

6

7

NUMBER OF Si ( O + j ^ - O - LINK AGES /REPEAT UNIT

Figure 2.

Formulation

Correlation of weight loss at 700°C

Parameters

The phenyl modified polymers possess the optimum combination of high temperature and elastomeric p r o p e r t i e s and were used i n the study of f o r m u l a t i o n parameters. These v a r i a b l e s can have an important e f f e c t on the thermal s t a b i l i t y and property p r o f i l e o f v u l c a n i z e d systems. For example, the use of r e i n f o r c i n g s i l i c a s , peroxide content, and o x i d a t i v e s t a b i l i z e r s have been shown to be important Q , JJ), 11)· However, p o l y m e r - s i l i c a i n t e r a c t i o n s had the most pronounced e f f e c t on r e t a i n i n g p r o p e r t i e s during high temperature aging s t u d i e s . As shown i n F i g u r e 3, h e a t a g i n g a t 315°C i n a i r o f a sample r e i n f o r c e d with h y d r o p h i l i c s i l i c a (amorphous) leads t o a r a p i d l o s s o f e l o n g a t i o n a f t e r 150 hours. However, modifying the s i l i c a by t r i m e t h y l s i l o x a t i o n (hydrophobic s i l i c a ) results i n s u b s t a n t i a l i m p r o v e m e n t s — e v e n a f t e r 1000 h o u r s a t 315°C i n a i r , elastomeric p r o p e r t i e s were r e t a i n e d . The adverse e f f e c t of the h y d r o p h i l i c s i l i c a was a t t r i b u t e d to the condensation r e a c t i o n of s u r f a c e s i l a n o l groups on the s i l i c a and p h e n y l s i l a n e m o i e t i e s on the polymer backbone. This r e s u l t s i n increased c r o s s - l i n k i n g v i a formation of s i l o x a n e bonds between the polymer and s i l i c a .



Solvent

Resistance

R e s i s t a n c e t o s o l v e n t s i s i m p o r t a n t i n s e v e r a l end use situations. The d e g r e e o f s w e l l i n g i n v a r i o u s s o l v e n t s can be m o d i f i e d by c h a n g e s i n t h e p o l y m e r b a c k b o n e and the t y p e o f reinforcement. The e f f e c t o f h y d r o p h o b i c and h y d r o p h i l i c r e i n f o r c i n g s i l i c a s on t h e s w e l l i n g o f v u l c a n i z e d t r i f l u o r o p r o p y l modified carborane-siloxane p o l y m e r (I., η = 2 , R = C H 3 , R' = CH2CH2CF3) appears i n T a b l e I I . In acetone the s w e l l i n g i s s i g n i f i c a n t l y l e s s when h y d r o p h i l i c s i l i c a i s u s e d i n r e i n f o r c e ment. A s i m i l a r t r e n d was n o t e d i n t o l u e n e .

TABLE I I

E f f e c t o f Type o f R e i n f o r c i n g A g e n t on

Solvent Acetone Toluene

Swelling

S w e l l i n g , %* Hydrophobic S i l i c a Hydrophilic 2 89

71 130

*ASTM D-471; V u l c a n i z a t e s w i t h 30 p h r

Silica

silica.


30.

PETERS

m-Carhorane Siloxanes

455

Modification of the polymer backbone by the incorporation of trifluoropropyl groups leads to substantial decreases in swelling. In vulcanized systems reinforced with hydrophilic silica (30 phr) the swelling decreased with increasing CH2CH2CF3 content as shown in Table III.


TABLE III Swelling as a Function of Polymer Modification R' 3 CH3 CH2CH2CF3 CH2CH2CF3

2

CH

2 2 2

f c H 3 (67) l c 6 H 5 (33) CH2CH2CF3 CH3 CH2CH2CF3

Swelling, % Toluene Reference Fuel Β 1 6 0

98 63 23

1 1 3

80 43 20

Conclusions Properties of carborane-siloxanes can be readily modified through changes in the polymer backbone and by the use of supple mentary agents in order to optimize the property-performance profile for different use situations. Thus a strong technology base now exists for carboranesiloxane polymers which adds measureably to the arsenal of design engineers for advanced systems. The visionary support of the Office of Naval Research has been largely responsible for the important advancements in this area. Literature Cited 1. 2. 3. 4. 5.

Peters, Ε. N., J. Macromol. Sci., Rev. Macromol. Chem., in press. Knollmueller, K. O.; Scott, R. N.; Kwasnik, H . ; Sieckhaus, J. F.; J. Polym. Sci., A-1, 1971, 9, 1071. Peters, E. N.; Hedaya, E; Kawakami, J. H . ; Kwiatkowski, G. T.; McNeil, D. W.; Tulis, R. W.; Rubber Chem. Technol., 1975, 48, 14. Papetti, S; Schaeffer, Β. B.; Gray, A. P.; Heying, T. L . ; J. Polym. Sci., A-1, 1966, 4, 1623. Roller, M. B. and Gillham, J. Κ., Polym. Eng. Sci., 1974, 8, 567.


456


6.

Peters, E. N.; Kawakami, J. H.; Kwiatkowski, G. T.; McNeil, D. W.; Hedaya, E; J. Polym. Sci., Polym. Phys. Ed., 1977, 15, 723. Scott, R. N.; Knollmueller, K. O.; Hooks, Jr., H.; Sieckhaus, J. F.; J. Polym. Sci., A-1, 1972, 10, 2303. Peters, Ε. N.; Stewart, D. D.; Bohan, J. J. Moffitt, R.; Beard, C. D.; J. Polym. Sci., Polym. Chem. Ed., 1977, 15, 973. Andrianov, Κ. Α.; Pavlova, S.-S. Α.; Zhuravleva, I. V.; Tolchinskii, Yu. I.; Astapov, Β. Α.; Polym. Sci. U.S.S.R., 1977, 19, 1037. Peters, Ε. N.; Stewart, D. D.; Bohan, J. J.; Kwiatkowski, G. T.; Beard, C. D.; Moffitt, R.; Hedaya, E . ; J. Elastomers Plast., 1977, 9, 177. Peters, Ε. N.; Stewart, D. D.; Bohan, J. J.; McNeil, D. W.; J. Elastomers Plast., 1978, 10, 29.

7. 8.


9. 10. 11.

RECEIVED

July

12, 1979.


Modification of Polymers - American Chemical Society

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