Silicone and Fluorosilicone Elastomers - ACS Publications - American

8 Silicone and Fluorosilicone Elastomers Structure and Properties

Downloaded by MICHIGAN STATE UNIV on February 19, 2015 | http://pubs.acs.org Publication Date: August 29, 1984 | doi: 10.1021/bk-1984-0260.ch008

K. E. POLMANTEER and J. R. FALENDER Dow Corning Corporation, Midland, MI 48640

Silicones and fluorosilicones have traditionally been classified as high performance materials due to their suitability for use under extreme conditions and their processability has been particularly interesting as a result of the very flexible siloxane chain. The present paper discusses selected examples where more recent advances in science and technology have broadened the understanding and uses. Emphasis is given to relating the molecular chemistry and physics to the characteristics of the bulk materials. Stability is discussed from the viewpoint of what can be done to broaden the performance limits. Aqueous dispersions are pre sented as an important method of enhancing processability even beyond that inherent in the siloxane chain. Foams involve an example where very interesting crosslinking and foaming chemistry is combined with rheological understanding to fulfill performance needs beyond that of the traditional compounds. Electrical features are finding use in many "high technology" applications and it is becoming more obvious that there is a need to be able to relate the properties to molecular structure. Finally, the optical properties of silicone composites are becoming more critical and the controlling physics is taking on new importance. Polydiorganosiloxanes such as polydimethylsiloxanes, have estab lished a very respectable position as high performance polymers. They have been successfully utilized in a variety of forms including low and intermediate molecular weight fluid polymers and matrix polymers for silicone elastomers. This paper focuses particularly on a few interesting high performance and processing aspects of

0097-6156/84/0260-0117$07.50/0 © 1984 A m e r i c a n C h e m i c a l Society

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

118

POLYMERS FOR FIBERS A N D

ELASTOMERS

s i l i c o n e and f l u o r o s i l i c o n e elastomers. A description w i l l be provided of some recent elastomer developments resulting from research at the Dow Corning Laboratories in Midland, Michigan, as well as. other researchers' work pertaining to structure-property e f f e c t s . In 1979, a review paper (I) included over 1000 l i t e r a t u r e c i t a tions describing elastomer developments for the period 1967-1977, and i t also l i s t e d e a r l i e r reviews. In 1981 a paper (2), "Current Perspectives On S i l i c o n e Rubber Technology" was published. These references (1-2) provide suitable background leading to the present paper.


Discussion Influence of Structure of S i l i c o n Containing Polymers on S t a b i l i t y . Certain appTications require s t a b i l i t y even beyond that found in polydimethylsiloxane. It has been recognized for many years that an approach to improve the s t a b i l i t y of polydiorganosiloxanes would be to reduce the ionic character by replacement of some of the backbone oxygen atoms with oxidatively stable spacers such as arylene groups ( e . g . , p-phenylene) (3-13). These references describe much of the early synthesis development effort resulting in improved methods (12) (reported by Merker from Dow Coming's fellowship at Mellon Institute) giving 60-70% y i e l d s using the following in s i t u Grignard reaction for the preparation of p-(bisdimethylhydrogensilyl)benzene:

Br©Br

+ 2 Mg + 2 (CH ) HSiCl 3

2 MgClBr

+

:

2

(CH ) HSi®SiH(CH ) (I) 3

2

3

2

The hydrolysis of the dihydride (I) and condensation to form c y c l i c structures for subsequent polymerization s i m i l a r to the p o l y merization methods used for the polydiorganosiloxanes resulted in poor y i e l d s as did alkaline thermal cracking methods. However, (12-13) hydrolysis of (I) to the corresponding dihydroxy compound fol 1 owed by condensation using e s s e n t i a l l y non-equilibrating type catalysts such as tetramethylguanidine di-2-ethylhexoate e a s i l y provided high molecular weight homopolymers, C ( C H ) S i © S i (CH ) -01n, (TMPS, tetramethyl-parasilphenylene), or block copolymers containing blocks of (CH3) Si0 (PDMS, polydimethylsi 1oxane). Both of these polymers are c r y s t a l l i n e at ambient temperature. The homopolymer melts at about 148°C, while the block copolymers melt at temperatures dependent on the block size of the c r y s t a l l i n e TMPS segments, with a high temperature approaching 140 °C. Thermal s t a b i l i t y of the above homopolymer was shown (12) to be superior to a polydimethylsiloxane (catalysts carefully removed from each) by the reduced generation of v o l a t i l e s and reduced levels of crosslinking resulting from oxidation. Weight loss for the catalyst free homopolymers was as follows: 3

2

2


3

2

8.

POLMANTEER A N D FALENDER

Silicone & Fluorosilicone

Elastomers

119

Homopolymer S t a b i l i t y In A i r Time Hours


200 255 305

% Weight Loss rPPMSJn" TTMPSIn

200 128 24

0.8 24.1 26.9

0.4 6.6 9.7

Although better s t a b i l i t y was found in the absence of c a t a l y s t s , Merker (13) noted that e q u i l i b r a t i n g catalysts such as potassium s i l a n o l a t e would rearrange a tough e l a s t i c block copolymer to an amorphous, clear gum while not reducing the molecular weight. Merker, e t . a l . (13) reported that block copolymers of TMPS-DMS segments exhibited elastomeric properties and considerable toughness because of the c r y s t a l l i n e TMPS blocks. The t e n s i l e strengths increased with molar concentration and block lengths of TMPS. Examples of some mechanical property data are as follows: Effect of TMPS (B units) Content in Block Copolymers with DMS (A units)

TMPS Mole% 1ft. % 18 25 33 44

40 50 60 70

Min.Avg. Arrangement (A-B)

Cn] dl/g.

Tensile MPa

Elong.

%

Shore A Duro.

18-4 18-6 18-9 18-14

1.91 2.11 2.00 1.53

7.8 12.7 14.4 18.8

962 750 643 490

50 72 86 93

Kojima and Magill (14-15) have done extensive morphological characterization of TMPS-DMS block copolymers. Another type of group studied as a relacement for some of the oxygen backbone atoms is the carborane cage structure [ e . g . , meta-CBioHifjC-]. Papitti (16) e t . a l . reported the synthesis of meta SiB2 polymers: [-(CH3)2Si-CB H C-Si(CH3)20Si(CH3)20] 10

10

n

The behavior of these polymers was studied and reported by Tobolsky and coworkers (17-18). They concluded that SiB2 had better high temperature properties than a polydimethylsiloxane based elastomer. Thermal s t a b i l i t y decreased as the distance between c a r boranyl units was increased with dimethylsiloxane (DMS) u n i t s . In


P O L Y M E R S FOR FIBERS A N D E L A S T O M E R S

120

1973 Roller and Gillham reported on the thermomechanical behavior in nitrogen (!19) and in a i r (20) of a systematic series of l i n e a r poly(carborane-siloxane)'s containing icosahedral ( - C B ^ H ^ C - ) cages in place of some of the chain oxygen atoms: A-0[R(CH )Si-Z-(Si(CH )R0) ] A 3

3

n

where x=l,3,4,5, ; A=endgroups (reactive and i n e r t ) ; Z=meta-, para-carborane (for x=3); R=CH , R=C2H4CF (for x=3), one in five R's=C6 5» remainder - C H (for x=4); molecular weight= ^10,000, ^50,000 (for x=3). The results in nitrogen indicated the phenyl pendant groups improved s t a b i l i t y . A l l of the meta-carborane polymer was more stable by about 50°C. The influence of the meta and para-carborane chain units on Tg, and Tm compared with p o l y d i methyl siloxane (DMS) was as follows: 3

H


x

W

l

t

n

t

n

e

3

3

Key Chain Segment

Tm

°C Tc[

meta-carborane para-carborane DMS

40 110 -40

-68 -35 -125

It was interesting that s t a b i l i t y i n a i r (20) indicated that for the a l l methylated polymers, PDMS was more oxidatively stable than the carboranes (e.g. about 350°C vs 280° to 300°C). The work reported thus far has focussed on the substitution of either aryl groups or carborane cage structures for some of the backbone oxygen atoms. It w i l l be shown next that fluorohydrocarbon alkyl spacers that possess greater thermal s t a b i l i t y than t h e i r normal alkyl counterparts may also be substituted for some of the backbone oxygen atoms to provide polymers of not only improved s t a b i l i t y , but good solvent resistant properties. This work was done at Dow Corning Corporation with Dr. Ogden R. Pierce as the Principal Investigator under the sponsorship of the A i r Force Materials Laboratory, Wright-Patterson A i r Force Base, Ohio. There are several publications (21-25) that describe the work in d e t a i l . The work led (25) to polymers of the following type, (R'RSiCH CH ZCH CH2Si R'R0) 2

2

2

n

where R=R'=CH , CF CH CH , and Z=perfluoroalkylene. The f l u o r o hydrocarbon monomers were prepared by the following reaction sequence: X(CF ) X 3

3

2

2

2

init.

n

CH =CH 2

2

XCH2CH2(CF2) CH2CH X n

2

base H C= CH (cF ) CH= CH 2

2

n

2

Br or I, n = 1-10


8.

121

Silicone & Fluorosilicone Elastomers

POLMANTEER AND FALENDER

Thermal i n i t i a t i o n of ethylene addition to the diiodo p e r f l u oroalkanes, n greater than 2, was the best high y i e l d procedure. For n equal 1, the method of Henne and DeWitt (26) was used. The next step in the synthesis involved the hydrosiTane addition to the above diene, for example:

H C=CH(CF2) CH=CH2 2

n

CF CH2CH2(CH )SiHCl 3

3

CH w CH ClSiCH2CH2fCF2) CH CH2SiCl CH CH CH CH CF CF


3

3

n

2

2

2

2

2

3

3

This p a r t i c u l a r hydrosilane addition catalyzed with free radicals from d i - t - b u t y l peroxide gave high y i e l d s without complications. Homopolymers were prepared by f i r s t hydrolyzing the dichloride monomer using aqueous sodium bicarbonate in ether as solvent. Bulk condensation of the resulting monomer diol was catalyzed by tetramethyl-guanidine t r i f l u o r o a c e t i c acid y i e l d i n g high consistency elastomeric gum. This may be shown schematically as follows (25):

R*

R'

Cls'iCH CH2(CF2)xCH CH2s!iCl 2

'

2

I

H0 2

Diols

-H20_ R'

'R

i

iiCH2CH2(CF2) CH CH2s!iO x

2

Il(a-f) II-

a, b, c, d, e, f,

x x x x x x

= = = = = =

1 2 4 6 8 10

R' = C H , R=CF CH CH 3

3

2

2

It is interesting that i t was reported that no evidence of c y c l i z a t i o n of the diols was observed during polymerization. The marked influence on the h e t e r o l y t i c s t a b i l i t y by the fluorohydrocarbon alkyl spacers i s amply pointed out by the following e x p e r i ment. A sample of polymer IId for (x=6) formed no appreciable amount of v o l a t i l e reversion products when heated at 270°C under high vacuum i n the presence of potassium hydroxide. Under these conditions, both polydimethylsiloxane and p o l y m e t h y l ( 3 , 3 , 3 - t r i f l u oropropyl)siloxane generate and lose v o l a t i l e reversion products almost q u a n t i t a t i v e l y .


POLYMERS FOR FIBERS A N D E L A S T O M E R S

122


Polymers II a - f were found by X-ray d i f f r a c t i o n to be nonc r y s t a l l i n e amorphous materials. Similar structured polymers were prepared for free radical vulcanization by the introduction of vinyl crosslinking s i t e s . The polymers were formulated into high consistency elastomers reinforced with s i l i c a and were free radical vulcanized. The properties for only l i b and IId are shown in Table I with a commercial elastomer prepared from p o l y m e t h y l ( 3 , 3 , 3 - t r i f l u oropropyl)siloxane (LS) shown for comparison. Also included i s an elastomer prepared from the following copolymer ( I I I ) ,

TrT

3

I

SiO

SiCH

1

JH

CH

2

"2

CH

2

2

|_£ 3

A

F

2

. 1 J

(III)

which was prepared to evaluate t h i s as an approach to reducing Tg. The data in Table I indicate that the fluorohydrocarbon substitution for some of the oxygen atoms in polydisubstitutedsiloxanes does indeed improve the retention of physical properties both in a i r and under confinement at 250°C while maintaining solvent swell propert i e s comparable with a t y p i c a l f l u o r o s i l i c o n e (LS) elastomer. However, low temperature f l e x i b i l i t y as judged by Tg does suffer. The preparation of copolymers with methyltrifluoropropylsiloxane units such as in above copolymer III does reduce Tg by about 5°C. A more effective method of lowering Tg can be achieved by replacing the perfluoroalkyl chain units with perfluoroether units (27). The influence of a variety of perfluoroether spacers and C F C F on Tg i s shown i n Table II. Tg values of the perfluoroether containing polymer were lower than the C F C F containing polymer ( V i l a ) . The lower glass t r a n s i t i o n temperatures were exhibited by the polymers containing the more unsymmetrical fluoroether segments ( e . g . , V i l e in Table II), even though the difluoromethylene to oxygen r a t i o i s comparatively high in these molecules. Thermogravimetric analysis provides a comparison of the oxidative and thermal s t a b i l i t y of the raw polymers (Table III) with that of the C F C F (Vila) polymer. In general, the differences are quite small, i n d i cating that i t i s possible to substitute a fluoro-ether segment for the fluorocarbon segment within the hybrid fluorocarbon-fluoros i l i c o n e polymer with r e l a t i v e l y l i t t l e loss of thermal and oxidat i v e performance, while s i g n i f i c a n t l y extending low temperature capabilities. 2

2

2

2

2


2


8.

Table I,

IIB


M.W.a Sp. G. g

(°C)

b

Ori gi n a l , post cured at 200°C/ 8 hr

Durometer Tensile Strength, MPa Elongation, %

% Volume Swell

Methylisobutyl Ketone Toluene Heptane

After 24 hr at 250°C in Air

Durometer Tensile Strength, MPa Elongation, % %Wt. Loss

After 24 h r at 250°C in sealed gl ass container

Durometer Tensile Strength, MPa Elongation, %

c

d

123

High Consistency Elastomers

Polymer

T


LSe

Illf

IID

70,000

800,000

13,000

100,000

1.45

1.59

-27

-24

-29

-71

62

58

53

45

12.3 300

17.6 300

11.1 230

10.3 350

1.40

254 77 16

285 31 13

255 28 4

290 17 10

62

65

60

42

10.0 220 1.6

3.2 260 1.1

7.0 200 2.7

16.1 260 2.2

46

54

5.8 300

9.3 300

62 3.4 140

20 0.3 100

M.W. was d i f f i c u l t to obtain because of the i n s o l u b i l i t y of the polymer in common organic solvent. M.W. was determined either by vapor pressure or membrane osmometry. •Determined by d i f f e r e n t i a l scanning calorimetry. Seventy-two hours immersion at room temperature dTest for reversion resistance. P o l y ( 3 , 3 , 3 - t r i f1uoropropyl)methylsi 1oxane Copolymer used was CC(CF3CH2CH2)(CH3)siCH CH2(CF2)6CH2CH Si(CH )(CH2CH CF3)0]2[(CF CH2CH2)(CH3)Si0]L[ „ (*")•

a

c

e

2

2

3


2

3

124

P O L Y M E R S F O R FIBERS A N D E L A S T O M E R S

Table I K Glass Transition Temperature (DSC Scan at 10°C/MIN) CH3

CH

Si(CH2)

2

CH

CH2 3

POLYMER

2

CH

2

CF

3

N

Z

Vila


(VII)

2

CH2 CF

3

Z (CH ) SiO

2

-CF2CF

,

2

-[CF )30(CF2)

c d e

-(CF£) 0(CF ) 0(CF ) -(CF ) 0(CF ) 0(CF ) mixture of - C F 0 ( C F ) 0 C F -

2

2

2

-39°

2

2

2

2

5

2

2

2

2

5

5/1

-40° -52° -47°

2

3/1 4.5/1 4.5/1

JF3

C'F3

and

-(CF H0CFCF 0CF2

2

Table I I I . Thermal Gravimetric Analysis (10°C/MIN) Temperature at 50% wt. l o s s , °C

Temperature at 10% Wt. l o s s , °C

m

POLYMER*

m

IHg

310°

IVg

330°

412°

375°

497°

Vg

330°

450°

380°

502°

Vila

324°

474°

442°

504°

NITROGEN

NITROGEN

355°

CH3 UH CHf 0Si(CH ) (CF )jt[0(CF ) ] 0(CF ) (CH ) Si CH CH _ CH CH CF CF 2

2

2

2

-26°

%

b

2

CF

Tg (DSC), °C

2

m

n

2

2

2

2

2

2

2

3

3

Illg,* ~T7g,£ "Tg,£

=3, n =0 = 2, m = 2, n = 1 = 2, m = 5, n = 1


/JT

8.



125


Siloxane Elastomer Processing From Aqueous Dispersion The i n t r i g u i n g s c i e n t i f i c (28) and engineering features (29) (such as processing ease) associated with polymer-in-water emulsTons have led to a s i g n i f i c a n t amount of effort aimed at s i l i c o n e elastomers. Ingredients incorporated during and after polymerization have included dimethylsiloxane oligomers, i o n i c surfactants and c a t a l y s t s , organotin compounds, c o l l o i d a l s i l i c a , and water. In one sense, the c o l l o i d a l s i l i c a serves the same function as fumed s i l i c a does in more conventional s i l i c o n e rubber technology. That i s , the c o l l o i d a l s i l i c a increases modulus, ultimate strength and swell resistance as seen in Figure 1 and Table IV. The hypothesized chemistry i s i l l u s t r a t e d in Figures 2 and 3. S i l i c a t e s graft to s i l a n o l groups on the polymer chain at the s u r face of emulsion p a r t i c l e s . While s t i l l suspended in water, low molecular weight s i l i c a t e s (depolymerized from c o l l o i d a l s i l i c a in the alkaline environment) could migrate into the p a r t i c l e s and multiple graft s i t e s would lead to c r o s s l i n k i n g . Higher molecular weight s i l i c a t e s would remain at the oil-water interface and provide s t a b i l i z a t i o n of the emulsion. Organotin compounds render the s i l i cates hydrophobic and promote the transfer of these species to the oil-water i n t e r f a c e . At the i n t e r f a c e , the t i n compound catalyzes reactions between s i l a n o l s on the polymer and s i l i c a t e . The result would be p a r t i c l e s crosslinked before water removal. After water removal, the p a r t i c l e s adhere to one another both through hydrogen bonding and siloxane bonds which would be expected to form under the a l k a l i n e condition of the composition. The above chemistry i s believed to lead to an inverted s t r u c t u r e . Crosslinked polymer spheres are separated by a s i l i c a or s i l i c a t e rich phase with siloxane bonds grafting the two phases together. This would lead to some of the unusual properties which have been observed including a high stress at low extension and high water transmission through a hydrophilic continuum. (28) From a practical standpoint, the water based s i l i c o n e p r o v i des material of lower v i s c o s i t y than pure s i l i c o n e elastomers and free of hazards associated with handling solvent d i s p e r s i o n . Because of processing advantages as well as the easy clean-up features (commonly associated with latex p a i n t s ) , the materials are being considered for commercialization for applications such as construction coatings, water containment and several other areas. (28) Siloxane Elastomer Foams ^ Structure and Properties The high performance properties of s i l i c o n e foams depend not only on the siloxane polymer i t s e l f , but on some very interesting chemistry required following polymer synthesis (30-32). To achieve the desired mechanical properties and foam density, the kinetics of crosslinking and foaming reactions must be carefully balanced. = SiH + HOSie

Pt

= Si H + CH =CHSi = 2

-SiH + H 0 2

Pt

sSiOSi=+H Pt

2

^ =r Si CH CH Si

^^SiOH + H

2

2

s

2


POLYMERS FOR FIBERS AND ELASTOMERS


126

Strain ( A Length/Initial Length)

Fig. 1

Effect of s i l i c a on t e n s i l e properties of films cast from s i l i c o n e latexes. The curve marked 0 pph was obtained from a film containing 2 pph of sodium s i l i c a t e instead of collodal s i l i c a (pph = parts per hundred). Reproduced with permission from Ref. 28. Copyright 1981.

Table IV. Swelling Of Dried Films From Silicone Latexes Made With Sodium S i l i c a t e Amount of sodium s i l i c a t e phr 0.10 0.50 1.00 2.80 3.50 4.50

Gel fraction in cyclohexane, %

Swell in cyclohexane, %

46 73 77 83 84 83

Reproduced with permission from Ref. 28.

12,000 3,200 2,700 1,800 1,700 1,800

Swell in water, % 180 210 290 260 280 349

Copyright 1981.



8. POLMANTEER AND FALENDER

127

Oil-Water Interface

R SnOH 2

+ Si(OH)

\ S Water S PDMS Phase ^ Phase

4

O-CR

S


\

s (HO) SiOSnR 3

S

2

RjSnOSKOHJj

O-CR'

K

o Cross-Linked Polymer in Oil Phase

CH

CH

3

SiOH + R2SnOSi(OH) . 3

CH

3

I

I

3

^O-CR

,^SiOSi(OH) CH

3

3

Polysilicate Grafts at Interface Fig. 2

Fig. 3

Schematic representation of the process occuring while the system i s s t i l l in d i s p e r s i o n . Reproduced with permission from Ref. 28. Copyright 1981.

Schematic representation of the drying process. Reproduced with permission from Ref. 28. Copyright 1981.


128


In a number of commercially important examples, foaming enhances the performance of s i l i c o n e s or even makes them suitable where they would not otherwise function. For example, f i r e stop foam is used around wire and pipes penetrating through building walls and floors. The foaming reaction allows holes to be t i g h t l y sealed and the high thermal resistance greatly delays the spread of f i r e . In other a p p l i c a t i o n s , sound deadening, damping of mechanical v i b r a t i o n s , buoyancy, or mechanical f l e x i b i l i t y are c r i t i c a l properties. The degree to which the c e l l s are open or closed has a strong effect on properties such as sound deadening. Recent work has shown that the nature of the foaming reaction can be controlled by the ratio of S i H to »SiOH (designated as Rl) and by the ratio of polyfunctional s SiH molecules to monofunct i o n a l * S i H molecules (designated as R ) . For example, a high level of polyfunctional s S i H molecules causes v i s c o s i t y to increase more rapidly with time as the curing and foaming reactions take place (see Figure 4). It also causes the gel time to decrease and the amount of gassing before gelation to decrease (Figure 5). The amount of open c e l l structure goes down as the srSiH to - S i O H r a t i o increases. As the level of polyfunctional s S i H increases, the amount of open c e l l structure f i r s t increases then decreases (See Figure 6). (32)


s

2

Influence Of S i l i c o n e Structure On E l e c t r i c a l

Performance

Most s i l i c o n e polymers act as very good i n s u l a t o r s . Polarity of the siloxane backbone apparently i s shielded by methyl groups. In a d d i t i o n , the hydrophobic nature of the surface helps to repel water (and dissolved i o n i c contaminates) which assures the retention of insulation properties under d i f f i c u l t conditions. One application where these properties have found recent importance has been for insulator sheds. Even after repeated exposure to s a l t fog and high voltage s t r e s s , the materials retain t h e i r resistance to conductive and arc f a i l u r e (33). The effect oTTiumidity depends strongly on polymer structure. While the s o l u b i l i t y of water is below 1 part per m i l l i o n in caref u l l y p u r i f i e d , low s i l a n o l dimethyl siloxane polymers, at high humid i t y i t i s about 250 parts per m i l l i o n in commercial grade polymer (34). Here the water content goes up almost in d i r e c t proportion to the" r e l a t i v e humidity (see Figure 7) (35), and t h i s leads to an increase in d i e l e c t r i c loss (Figure 8 ) T 3 5 ) and d i s s i p a t i o n factor (Figure 9) (36). Table V reports the effect of s i l a n o l and metal ion content Zr\ volume r e s i s t i v i t y at 50% r e l a t i v e humidity. Metal ions in the range of around 60 parts per m i l l i o n decreased volume r e s i s t i v i t y (e.g. gum B), while s i l a n o l content exhibited the oppos i t e effect ( e . g . , gums A and C). The side groups on the polymer i t s e l f can also strongly influence the e l e c t r i c a l response of the m a t e r i a l . Volume r e s i s t i v i t y i s considerably lower on polymers with phenyl side groups in place of methyl while d i e l e c t r i c strength i s exceptionally high for the phenyl polymer (See Table VI) (37). O p t i c a l l y Clear S i l i c o n e Elastomers From New S i l i c a Technology This paper has thus far focused p r i n c i p a l l y on the s t r u c t u r e property behavior as i t relates to the polymeric matrix with a t t e n -


8.


POLMANTEER AND FALENDER

129

R = 1.0 2

6

10 i

R

Polyfunctional SiH * ~ Monofunctional SiH

!


10

Viscosity (CP.)

4

10

:

10

10 0

30 60 90 120150 180 Reaction Time (Sec.)

Fig. 4 Effect of R on the cure rate at room temperature. Reproduced with permission from Ref. 32. Copyright 1982 J . C e l l u l a r Plastics. 2

% Gassing Before Gelation

Fig.

MOO

Gel Time (Sec.)

Effect of R on the percent gassing before gelation and gel time at room temperature. Reproduced with permission from Ref. 32. Copyright 1982 J . C e l l u l a r Plastics. 5

2


130


Ri 7'


61 5i

41 3i

30 4050606050 40

2H

30

% Open-Cell

1 0.5

1.0 R

1.5

2.0

2

Fig. 6 Percent open-cell structure as a function of Ri and R . ' ' permission " " - - 32 Copyright 1982 J . C e l l u l a r Reproduced" with from Ref. Plastics 2

Water Content in Silicones

H 0 (ppm) 2

0

20

40

60

80

100

Relative humidity (%)

Fig.

7

Water content as a function of a r e l a t i v e

humidity.

Reproduced with permission from Ref. 35. Copyright 1977 IEEE.


8.

Silicone & Fluorosilicone


Elastomers

131

5

Tan6 (10 )

12108"

(75% RH i


Sm 65° C 38%i RH Dry

4m 2m

Room 25° C

•

•

0

4

8

•

I

I

•

I

12 16 20 24 28 32 Field (kV/cm)

Fig. 8

The d i e l e c t r i c loss at high f i e l d s , and humidities.

Reproduced with permission from Ref. 35.

at various

temperatures

Copyright 1977 IEEE.

100 HZ Dissipation Factor

0

20

40 60

80 100

% Relative Humidity Fig. 9

The effect of humidity of the dissipation factor of p o l y d i methyl siloxane. Silanol number i s a measure of the silanol incorporated i n polymer chains. Reproduced with permission from Ref. 36. Copyright 1974 National Academy of Sciences


132

POLYMERS F O R FIBERS A N D E L A S T O M E R S

Table V. The Effect of Residual ofPolydimethylsi 1oxane Metal Ion,ppm

Reference

Silanol on the Volume R e s i s t i v i t y

Silanol* Number

50% RH Volume R e s i s t i v i t y , ohm-cm

Empty Cel

1 x 10*7

[(CH ) Si0]

Silicone and Fluorosilicone Elastomers - ACS Publications - American

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