Organically Modified Silicates as InorganicâOrganic Polymers - ACS

Chapter 27

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 11, 2015 | http://pubs.acs.org Publication Date: January 7, 1988 | doi: 10.1021/bk-1988-0360.ch027

Organically Modified Silicates as Inorganic-Organic Polymers H. K. Schmidt Fraunhofer-Institut für Silicatforschung, Neunerplatz 2, D-8700 Würzburg, Federal Republic of Germany The combination between inorganic and organic polymeric materials on an atomic scale depends strongly on methods for synthesizing inorganic polymeric networks suitable to the thermal stability of organic materials. The sol-gel process as a "soft-chemistry" method has been proved to be a proper tool for building up inorganic network incorporating organic components. A review over examples for material developments and possibilities of tailoring by chemistry using sol-gel techniques in combination with organic components (organically modified silicates) is given.

N o v e l m a t e r i a l s have always p l a y e d a n i m p o r t a n t r o l e f o r t h e devel o p m e n t o f new t e c h n o l o g i e s . S i n c e t h e r e q u i r e m e n t o f m o d e r n t e c h n o l o g i e s w i t h r e s p e c t t o m a t e r i a l p r o p e r t i e s became more a n d more s p e c i f i c i t was n e c e s s a r y t o d e v e l o p c o m p o s i t e s : P r o p e r t i e s o f d i f f e r e n t types o f b a s i c m a t e r i a l s have t o be combined i n o r d e r t o f u l f i l these s p e c i f i c requirements. Moreover, n a t u r a l raw m a t e r i a l s , e s p e c i a l l y i n t h e f i e l d o f c e r a m i c s , c o u l d n o t meet t h e r e q u i r e m e n t s f o r a l o t o f d e s i r e d purposes (e.g. p u r i t y , homogeneity, r e a c t i v i t y ) , so n o v e l r a w m a t e r i a l s were d e v e l o p e d b y c h e m i c a l s y n t h e s i s . One o f t h e m o s t i m p o r t a n t c h e m i c a l r o u t e s t o c e r a m i c s i s t h e s o l - g e l p r o c e s s (1-5) w h i c h w a s p r o v e d t o o p e n u n i q u e n e w p o s s i b i l i t i e s t o improve m a t e r i a l o r p r o c e s s i n g p r o p e r t i e s (e.g. c o a t i n g s , p o w d e r s , f i b e r s a n d e v e n m o n o l i t h i c m a t e r i a l s ) . One o f t h e k e y s t e p s o n t h e w a y f r o m t h e (mono- o r o l i g o m e r i c ) p r e c u r s o r t o t h e s o l i d i s the polycondensation step, which defines t o a great deal t h e s t r u c t u r e o f a p r e p o l y m e r o r p o l y m e r t o be formed a n d t h u s i n f l u e n c e s p r o c e s s i n g a n d f i n a l m a t e r i a l p r o p e r t i e s e s s e n t i a l l y . One o f t h e m a j o r advantages o f s o l - g e l techniques i s t h e f a c t t h a t t h e network forming step o f t h e i n o r g a n i c polymer i s c a r r i e d o u t a tr a t h e r low temperat u r e s i n o r g a n i c o r aqueous s o l u t i o n s (compared t o c l a s s i c a l g l a s s melting o rceramic f i r i n g temperatures). This leads t o t h e p o s s i b i l i t y o f i n c o r p o r a t i n g o r g a n i c components i n t o i n o r g a n i c p o l y m e r s . The f o r m a t i o n o f p u r e i n o r g a n i c m a t e r i a l s b y t h e s o l - g e l r o u t e r e q u i r e s h e a t i n g : dense g l a s s e s can be p r e p a r e d around Tg; ceramic

0097-6156/88/0360-0333506.00/0 © 1988 American Chemical Society In Inorganic and Organometallic Polymers; Zeldin, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.


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INORGANIC AND ORGANOMETALLIC POLYMERS

m a t e r i a l s h a v e t o be s i n t e r e d a t h i g h t e m p e r a t u r e s , even i f i n most c a s e s s u b s t a n t i a l l y l o w e r f i r i n g t e m p e r a t u r e s c a n be a p p l i e d when s o l - g e l d e r i v e d r e a c t i v e p o w d e r s a r e u s e d . The p u r e i n o r g a n i c ma t e r i a l s a r e b r i t t l e due t o t h e i r h i g h ( t h r e e - d i m e n s i o n a l ) n e t w o r k c o n n e c t i v i t y . T h e r e f o r e , s u f f i c i e n t r e l a x a t i o n and c o n s e q u e n t d e n s i f i c a t i o n o n l y c a n o c c u r a t h i g h e r t e m p e r a t u r e . The i n t r o d u c t i o n o f o r g a n i c g r o u p i n g s c a n r e d u c e t h e o v e r a l l n e t w o r k c o n n e c t i v i t y and r e d u c e Tg and r e l a x a t i o n t o s u b s t a n t i a l l y l o w e r t e m p e r a t u r e s . Thus, d e n s e m a t e r i a l s c a n be p r e p a r e d a t t e m p e r a t u r e s a t w h i c h o r g a n i c com ponents are s t a b l e . D i f f e r e n t m a t e r i a l s have been d e v e l o p e d d u r i n g t h e l a s t d e c a d e u s i n g t h i s b a s i c r e a c t i o n p r i n c i p l e s (6-43). T h e y b e c a m e known a s o r m o s i l s ( o r g a n i c a l l y m o d i f i e d s i l i c a t e s o r ceramers). A b e t t e r e x p r e s s i o n , therefore, i s ormocer ( o r g a n i c a l l y m o d i f i e d ce ramics) , since the [siO^] tetrahedron i s not a non-dispensable com ponent . Structures I n o r g a n i c n e t w o r k s , e s p e c i a l l y g l a s s l i k e ones c a n be c h a r a c t e r i z e d by t h e r a t i o o f network f o r m i n g ( e . g . [ s ^ ^ ] ) network modifying ( e . g . ^ s i - o ~ N a ) u n i t s . N e t w o r k f o r m e r s ( e . g . S i O , Β Oy Al^O^, Ti0 ) are ( i n o p p o s i t i o n to the m a j o r i t y of organic units) three-dimensional crosslinking units. O r g a n i c g r o u p i n g s i n c o r p o r a t e d i n t o t h i s n e t w o r k (e.g. by ^ s i - R ) a c t as n e t w o r k m o d i f i e r s as shown i n F i g u r e l a . A c o n v e n i e n t method t o i n t r o d u c e o r g a n i c f u n c t i o n s i n t o i n o r g a n i c n e t w o r k s i s t h e use o f s u b s t i t u t e d s i l i c e o u s a c i d e s t e r s and t h e s o l g e l r o u t e . The b a s i c r e a c t i o n s , t h e r e f o r e , a r e g i v e n i n E q u a t i o n s 1 a n d 2. E q u a t i o n 1 d e s c r i b e s t h e s o l - g e l r e a c t i o n t o a b o r o s i l i c a t e glass, 0

t o

2

+ NaOR + B ( O R )

3

+ Si(OR)

4

H Q R

- H0

HO » NaOH + B ( O H )

+

3

Si(OH)

4

- HO

2

>

(1)

(Na O.B 0 -Si0 ).H 0 2

2

3

2

N a ^ c y S i C ^

2

gel

glass

R e.g.

methyl,

and E q u a t i o n 2 shows a g e n e r a l i z e d s o l - g e l r e a c t i o n i n c l u d i n g d i f ferent organic groupings u Me(OR) .. + v ( H X ) Si(OR)„ 4 η 4-n +

H0

-

HOR

2

I 0 -O-HMe0 ι

XH -Si-O ι XH

+ w(YX)

Si(OR)„ m

4-m

XY

(2)

i-0-4

X e . g . -CH -, -CH. *2 ' 6"4 Y e . g . -NH , -CHO, -COOH, v i n y l ,

Me m, epoxy,

= network forming η = 2

metal

methacrylate

F i g u r e l b g i v e s t h e scheme o f a n o t h e r t y p e o f s t r u c t u r e : O r g a n i c p o l y m e r i c c h a i n s a r e i n t r o d u c e d i n t o an i n o r g a n i c n e t w o r k by p o l y m e r i z a t i o n . N u m e r o u s t y p e s o f r e a c t i o n s c a n be u s e d f o r s y n t h e s i s l i k e v i n y l

In Inorganic and Organometallic Polymers; Zeldin, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

27.

SCHMIDT

Organically Modified Silicates

335

p o l y m e r i z a t i o n (30-34), epoxide p o l y m e r i s a t i o n (23), o r m e t h y l methacrylate polymerization (21). F i g u r e l c shows a t y p i c a l s t r u c t u r e o f two i n d e p e n d e n t ( i n t e r p e netrating) networks. A combination o f a l l types o f structures i s pos s i b l e , o f course. M a t e r i a l Development and P r o p e r t i e s I n t r o d u c t i o n o f Organic Network M o d i f i e r s . The i n t r o d u c t i o n o f o r ganic network m o d i f i e r s i n t o S i 0 g l a s s e s leads t o d r a s t i c changes o f p r o p e r t i e s . S i O g l a s s , f o rexample, has a thermal expansion coef f i c i e n t o f a b o u t O.5·10~" ·Κ~ , monômethy1-SiO g l a s s (|cH S i O . J ) a b o u t 100-10 ·Κ (40). ' In our i n v e s t i g a t i o n s t h e adsorption behaviour of C 0 as a func t i o n o f o r g a n i c m o d i f i c a t i o n i n p o r o u s S i O ^ s y s t e m s was m e a s u r e d . F i g u r e 2 shows t h e c o m p a r i s o n o f t h r e e a d s o r b e n t s , s y n t h e s i z e d u n d e r equal r e a c t i o n c o n d i t i o n s ( h y d r o l y s i s and condensation o f S i ( 0 C H ) ^ , CH - S i ( O C H ) a n d N H (CH ) - S i ( O C H^) (am) i n 50 v o l . % O ^ O H w i t h O.1 Ν HC1 a n d s t o i c h i o m e t r i c a m o u n t o f w a t e r ) . The i n f l u e n c e o f t h e m o d i f i c a t i o n o n a d s o r p t i o n b e h a v i o r i s o b v i o u s . The extreme h i g h l o a d a t l o w p C 0 v a l u e s c a n be a t t r i b u t e d t o a weak d i p o l e - d i p o l e i n t e r a c t i o n b e t w e e n t h e a m i n o g r o u p a n d C 0 , t h e h i g h l o a d o f CH^ g r o u p c o n t a i n i n g a d s o r b e n t s t o a h y d r o p h b i c i n t e r a c t i o n . The example d e m o n s t r a t e s t h e i n f l u e n c e o f s t r u c t u r a l changes o f i n o r g a n i c polymers by o r g a n i c m o d i f i c a t i o n on s e l e c t e d p r o p e r t i e s . A c h e m i c a l h e a t pump w a s d e v e l o p e d b y u s e o f t w o d i f f e r e n t t y p e s o f adsorbents w i t h C 0 (41). Another example f o r m a t e r i a l development i s t h e s y n t h e s i s o f a m i l d a b r a s i v e p o w d e r f o r s m o o t h i n g t h e human s k i n (acne p a t i e n t s ) (11,16,42).


2

2

2

2

5

3

2

2

2

2

2

O r g a n i c Network Formers. As i n d i c a t e d above, an a d d i t i o n a l o r g a n i c n e t w o r k c a n be b u i l t up b y o r g a n i c p o l y m e r s y n t h e s i s w i t h i n a n i n o r g a n i c n e t w o r k . T h e b a s i c p r i n c i p l e s a r e shown i n E q u a t i o n s 3 t o 5 w i t h a v i n y l , methyl methacrylate and epoxide p o l y m e r i z a t i o n :

-Zr-Si-0-Si- = 1

1

= -- S S ii -- 00 -- _S. i - 0 - Z r I polymerization ( T, r a d i c a l )

I (3)


INORGANIC AND ORGANOMETALLIC POLYMERS

336


> - ο Γ

î

Figure l a . groupinas • S i ο Ο.

Scheme o f a g l a s s l i k e

χ

y

structure, modified

by

F i g u r e l b . Scheme o f a g l a s s l i k e s t r u c t u r e , m o d i f i e d t i o n a l , c o v a l e n t l y bonded o r g a n i c polymer c h a i n s .

F i g u r e l c . Scheme o f a g l a s s l i k e s t r u c t u r e , m o d i f i e d t i o n a l , polymeric network ( i n t e r p e n e t r a t i n g ) .

organic

by a d d i

by an a d d i


27.

SCHMIDT

337

Organically Modified Silicates


(4)

R = glycol group containing organic radical R'rC^jCjfyOH

I -Ti-

I

ι

ι

r — / \ Z W Si - 0 - T i 7

polymerization

I I CH -Ti-0-Si—

Organically Modified Silicates as InorganicâOrganic Polymers - ACS

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