Static dissipating heat curable silicone rubber compositions

A static dissipating heat curable silicone rubber composition comprising a diorganopolysiloxane polymer, a filler and a peroxide curing catalyst and as the static discharging agent a polyether-polysiloxane copolymer.

BACKGROUND OF THE INVENTION 
The present invention relates to heat-curable silicone rubber compositions 
and particularly the present invention relates to heat-curable silicone 
rubber compositions which are hydrophilic and capable of dissipating 
static electricity. 
Heat curable silicone rubber compositions are well known. Basically such 
compositions comprise a diorganopolysiloxane polymer, and extending or 
reinforcing filler, or mixtures thereof, which filler can be treated or 
untreated, and a peroxide curing catalyst. It is also common to facilitate 
the processing of such compositions by using various well known silicone 
process aids. The resulting ingredients are milled or mixed together in a 
doughmixer, formed to the desired shape and heated at elevated 
temperatures above 100.degree. C. to cure the composition to a silicone 
elastomer. Such compositions have well known properties as insulation for 
various purposes, such as for instance electrical insulation for 
electrical wire cables, etc. It has also become known in the technology to 
make such heat curable silicone rubber compositions conductive. Such 
conductive heat curable silicone rubber compositions are produced by 
incorporating to such composition conductive carbon black, or a metal or 
metal particles in the composition. The resulting heat curable silicone 
rubber composition which is conductive while suitable for many purposes 
has the disadvantage it does not act as an electrical insulation material 
and in addition, the presence of the carbon black makes it very hard in 
the cured form such that it has a Durometer of 50 and above. 
Recently, in the industry it has become desirable to produce heat-curable 
silicone rubber compositions which are conductive enough to dissipate 
static electricity while at the same time the composition is soft that it 
has a Durometer in the neighborhood of 30. For instance, in hospital 
operating rooms, there is always the danger of an explosion due to the 
build-up of static electricity in various apparatus which may cause 
electrical charge to form a spark in the presence of potentially explosive 
gases or liquids. 
Accordingly, for many applications in such hospital operating rooms, it is 
desired to utilize heat-curable silicone rubber compositions because of 
their inertness to various chemicals and agents. However, some 
heat-curable silicone rubber compositions had the disadvantage that they 
could build-up electrical charges which might cause a spark and result in 
a possible fire or explosion. Accordingly, to remove the possibility of 
such fires or explosions due to the accumulation of static electricity, 
conductive heat-curable silicone rubber compositions were formulated for 
various parts in the operating room. Such conductive heat-curable silicone 
rubber compositions being able to dissipate static electricity and thus 
removing the possibility of a fire or an explosion. However, such static 
dissipating conductive heat curable silicone rubber compositions as 
explained above had the disadvantage that they were hard and abrasive to 
the human skin. 
Accordingly, it was highly desirable to have a heat-curable silicone rubber 
composition which was conductive enough to dissipate static electricity 
but still retained its inertness and insulative properties and also was 
soft. To produce such static dissipating heat-curable silicone rubber 
compositions, it was suggested by some that there be incorporated into 
heat-curable silicone rubber compositions as static electricity 
dissipating additives, glycerin and polyethylene oxide glycol compounds. 
While such materials did result in a heat-curable silicone rubber 
composition which was conductive enough to dissipate static electricity, 
it had several disadvantages. One of the disadvantages of such 
compositions is they tended to have low physical properties, that is a 
very low tear and a very low tensile strength. It was also found in some 
cases that the glycerine additive or the glycol polyether additives in 
some cases interfere with the peroxide cure of the composition to form a 
silicone elastomer. Accordingly, it was highly desirable to find 
substitutes for such glyverin and glycol polyethers which could be added 
to heat-curable silicone rubber compositions to make such heat-curable 
silicone rubber composition sufficiently conductive to dissipate static 
electricity while the compositions retain their physical properties and in 
which such heat-curable silicone rubber compositions still had the desired 
insulative properties and softness. Also it was desirable to find static 
electricity dissipating additives for heat-curable silicone rubber 
compositions which additives did not interfere with the cure of the 
composition. 
It is also desirable in the health care area to produce elastomers which 
are hydrophilic. Specifically, heat-curable silicone rubber compositions 
because of their inertness have a good suitability for the fabrication of 
parts where an elastomer is necessary. However, such silicone elastomers 
produced from heat-curable silicone rubber compositions have the 
disadvantage that they are not hydrophilic. Accordingly, it is desirable 
that such silicone elastomers have hydrophilic surfaces so they may become 
compatible for the various uses that they may be put to in the health care 
area. Thus, it is desired the heat-curable elastomer be hydrophilic such 
that they are compatible with various parts of the physical anatomy. 
Accordingly, for instance it is highly desirable that heat-curable 
silicone elastomers be hydrophilic so that they are compatible with blood 
plasma. Various methods were tried to make such heat-curable silicone 
elastomers hydrophilic, such as treating the surfaces of such silicone 
elastomers with various chemicals and ingredients so as to make the 
surface of the silicone elastomer hydrophilic. 
Accordingly, it is highly desirable to be able to incorporate a static 
dissipating ingredient which is non-toxic and compatible with standard 
heat-curable silicone rubber compositions so as to make such heat-curable 
silicone rubber compositions hydrophilic. 
Further, in the copying art for various rollers utilized in copying 
machinery, it is desirable to have present rollers made of a material 
which is static dissipating but have good physical properties. 
In addition, prior art static-dissipating heat-curable compositions tended 
not to bond very well to substrates even with the use of primers. 
Accordingly, it is one object of the present invention to provide for a 
heat-curable silicone rubber composition which is capable of dissipating 
static electricity. 
It is another object of the present invention to provide for a heat-curable 
silicone rubber composition which is capable of dissipating static 
electricity and is hydrophilic in nature. 
It is still another object of the present invention, to provide for a 
hydrophilic, static electricity dissipating, heat-curable silicone rubber 
composition which is suitable for the health care area and which has good 
physical properties, that is cured elastomer is soft. 
It is yet an additional object of the present invention to provide a 
process for producing a heat-curable silicone rubber composition which is 
capable of dissipating static electricity, is hydrophilic in nature and 
has good physical properties, as well as provides good bonds to substrates 
with the use of primer compositions. These and other objects of the 
present invention are accomplished by means of the invention set forth 
hereinbelow. 
SUMMARY OF THE INVENTION 
In accordance with the above object there is provided by the present 
invention a static dissipating curable silicone rubber composition 
comprising (1) 100 parts by weight of a diorganopolysiloxane polymer 
having a viscosity varying from 1,000,000 to 200,000,000 centipoise at 
25.degree. C. where the organo group being selected from the class 
consisting of monovalent hydrocarbon radicals and halogenated monovalent 
hydrocarbon radicals. (2) 5 to 150 parts by weight of a filler (3) from 
0.1 to 10 parts of peroxide curing catalyst (4) from 1 to 1.5 parts by 
weight of a polyether polysiloxane copolymer additive of the Formula, 
EQU A.sub.w.B.sub.v 
where A is the polysiloxane moiety and B is the polyether moiety where w is 
a whole number varying from 1 to 100 and v is a whole number varying from 
1 to 200. The polyether moiety may consist of only ethylene oxide units, 
ethylene oxide and propylene oxide units or consist of ethylene oxide, 
propylene oxide and butylene oxide units. Various linkages may be utilized 
to link the polyether moiety to the polysiloxane moiety, including Si -- O 
-- C linkages, -- Si (CH.sub.2).sub.t linkages where t varies from 2 to 20 
or 
##STR1## 
where t varies from 2 to 20. In the present case the most preferred 
linkage is the last linkage disclosed above, that is the 
##STR2## 
which allows the static electricity dissipating additives to have the 
maximum efficiency in carrying out that function in the heat-curable 
silicone rubber composition of the present case. The polysilocane 
polyether copolymer of the instant case can have any desired structure, 
thus it can be linear or it can be trifunctional and the polyether units 
can be connected either to the silicone atoms in the linear chain or to 
the terminal silicone atoms of the polysiloxane at one end of the 
polysiloxane, or, the polyether moieties may be connected at both ends of 
the polysiloxane moirty or they can be connected at both ends of the 
polysiloxane moiety and also to silicone atoms in the internal portion of 
the polymer chain. In addition, the silicone moiety can be trifunctional 
with a polyether moiety attached to the polysiloxane moieties at the end 
of each of the polysiloxane moiety chains. As stated above there may be 
utilized a filler with the instant composition which can be either a 
reinforcing or an extending filler such as for instance as fumed silica. 
The filler may be treated or untreated. Preferably there may be utilized 
as the filler, fumed silica treated with a cyclic polysiloxane. The two 
main types of reinforcing fillers are treated or untreated fumed silica or 
precipitated silica. These fillers may be utilized alone, or in 
combination with, or completely substituted by extending fillers such as 
lithopone and calcium carbonate. 
Generally, it has been found that the fumed silica and precipitated silica 
are preferred since they give the static electricity dissipating 
composition the best physical properties. These and other aspects of the 
present invention will be explained hereinbelow.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Diorganopolysiloxane polymer that may be utilized in the present invention 
may have a viscosity varying anywhere from 1,000,000 to 200,000,000 
centipoise at 25.degree. C. The organo groups of such diorganopolysiloxane 
are well known for instance these organo groups can be selected from alkyl 
radicals, methyl, ethyl, propyl; alkenyl radicals, such as vinyl, allyl; 
cycloalkyl radicals such as cyclohexyl, cycloheptyl and mono-nuclear aryl 
radicals such as phenyl, methylphenyl, ethylphenyl, etc. In addition, the 
organo groups can be selected from halogenated monovalent hydrocarbon 
radicals such as halogenated alkyl radicals for instance 3,3,3 
trifluoropropyl, etc. The diorganopolysiloxane polymer may have as organo 
groups any of the above radicals mentioned and can have a mixture of such 
radicals. 
Most preferably, the organo groups of such diorganopolysiloxane polymer may 
be selected from lower alkyl radicals of 1 to 8 carbon atoms, vinyl 
radicals and phenyl radicals or 3,3,3 trifluoropropyl radicals. More 
specifically, the diorganopolysiloxane polymer may have the structural 
formula 
##EQU1## 
where R.sup.5 may be any of the organo groups as specified above for the 
diorganopolysiloxane polymer and is most preferably selected from lower 
alkyl radicals of 1 to 8 carbon atoms, vinyl, phenyl and 3,3,3 
trifluoropropyl radicals, and n varies from 1.9 to 2.1. Production of such 
diorganopolysiloxane polymers is well known. Briefly, production of such 
polymers comprises hydrolyzing the appropriate diorganodichlorosilanes, 
then taking the hydrolyzate and cracking it with an alkali metal hydroxide 
so as to preferentially distill off cyclotetrasiloxanes. To the 
cyclotetrasiloxanes which are distilled in pure form there is added small 
amounts of an alkali metal hydroxide such as potassium hydroxide or 
potassium silanolate catalyst at a concentration of anywhere of 5 to 500 
parts per million of the total cyclic siloxanes present and the resulting 
mixture is heated at elevated temperatures of anywhere in the range of 
100.degree. to 200.degree. C. to produce high molecular weight 
diorganopolysiloxane polymers, having a viscosity of anywhere from 
1,000,000 to 2,000,000,000 centipoise at 25.degree. C. In such a reaction, 
there is preferably utilized chainstoppers to set the final molecular 
weight of the diorganopolysiloxane polymer that is formed. Examples of 
such chainstoppers is for instance hexamethyldisiloxane, 
octamethyltrisiloxane, divinyltetramethyldisiloxane, etc. These 
chainstoppers are used in appropriate quantities that is necessary to 
obtain the desired viscosity of the diorganopolsyiloxane polymer that is 
formed in the above reaction. The reaction which is an equilibration 
procedure may take anywhere from 1 to 12 hours and is terminated when the 
maximum amount of diorganopolysiloxane polymer is formed from the 
cyclictetrasiloxane. 
Accordingly, when this endpoint is reached, that is when about 85% by 
weight of the cyclictetrasiloxanes have been converted to the linear 
diorganopolysiloxane polymer, the basic catalyst is neutralized with an 
acid such as phosphoric acid and the undesirable volatiles are vented off 
and recycled for use in another equilibration reaction. The resulting 
residue polymer that is formed is a diorganopolysiloxane polymer of the 
foregoing viscosity. Fluorosilicone substituted polysiloxanes may be 
formed in much the same way by the use of cyclictetrasiloxanes or 
cyclictrisiloxanes as for instance as disclosed in the process of Evans 
Ser. No. 716,623 now abandoned which is incorporated in the present case 
by reference. 
With such a diorganopolysiloxane polymer the base ingredient in the 
composition of the instant case there may be utilized per a hundred parts 
of diorganopolysiloxane polymer from 5 to 150 parts by weight of a filler. 
Such a filler may be a reinforcing filler such as fumed silica and 
precipitated silica which may be treated or untreated, the common treating 
agents for such reinforcing filler being cyclictetrasiloxanes and 
silazanes. In addition, extending fillers such as titanium dioxide, 
lithopone, zinc oxide, zirconium silicate, silica aeaogel, iron oxide, 
diatomaceous earth, calcium carbonate, glass fibers, magnesium oxide, 
chromic oxide, zirconium oxide, aluminum oxide, alpha quartz and calcined 
clay may be utilized as a filler in the instant case. However, it is not 
preferred to utilize the conductive type of carbon black in the invention 
of the instant case since it would make the instant composition too hard. 
As has been said previously, per 100 parts of the diorganopolysiloxane 
polymer there is utilized from 5 to 150 parts by weight of a filler and 
more preferably from 10 to 100 parts by weight of a filler. The extending 
fillers can also be treated or untreated with various treating agents so 
as to make them more easily to disperse in the diorganopolysiloxane 
polymer, and to improve the final properties of the diorganopolysiloxane 
elastomer that is formed from the ingredients of the instant case. 
Preferably there is utilized as a filler in the invention of the 
composition of the instant case, fumed or precipitated silica as they 
enhance the physical properties of the resulting cured elastomer that is 
formed. 
Another ingredient in the composition of the instant case, so as to cure 
the composition, there may be added is from 0.1 to 10 parts by weight of a 
peroxide curing catalyst based on 100 parts of the diorganopolysiloxane 
polymer and more preferably, from 0.1 to 5 parts by weight of the peroxide 
curing catalyst. 
The curing of the silicone rubber composition of the present invention can 
be effected by chemical vulcanizing agents or by high energy electron 
radiation. More often, chemical vulcanizing agents are employed for the 
curing operation and any of the conventional curing agents can be 
employed. The preferred curing agents are organic peroxides conventionally 
used to cure silicone elastomers. Especially suitable are the dimethyl 
peroxides which may have the structural formulas, 
##STR3## 
wherein R represents the same alkyl group throughout, or alkyl groups of 
two or more different types and n is zero or a larger integer. 
Among the specific peroxide curing catalysts that are preferred are 
di-tertiary-butyl peroxide, tertiarybutyl-triethylmethyl peroxide, 
tertiary-butyl-tertiary-butyl-tertiary-triphenyl peroxide and di-tertiary 
alkyl peroxide such as dicumyl peroxide. Other suitable peroxide catalysts 
which effect curing through saturated as well as unsaturated hydrocarbon 
groups on the silicon chain are aryl peroxides which include benzoyl 
peroxides, mixed alkyl-aryl peroxides which include tertiary-butyl 
perbenzoate, chloroalkyl peroxides such as 1,4-dichlorobenzoyl peroxide; 
2,4-dichlorobenzoyl peroxide, monochlorobenzoyl peroxide, benzoyl 
peroxide, etc. 
To facilitate the mixing of the ingredients and more specifically the 
filler in the composition of the instant case and specifically into the 
diorganopolysiloxane polymer which is of a high viscosity, there is 
normally utilized a process aid to facilitate the mixing. Such a process 
aid's main function is to facilitate the mixing of the filler into the 
diorganopolysiloxane polymer without having the filler clump up. Normally 
the filler will be treated with cyclicpolysiloxanes or silazanes or fatty 
acids in the case of the extending fillers so as to allow the fillers to 
mix into the diorganopolysiloxane polymer with facility. In the 
flurosilicone diorganopolysiloxane polymers in accordance with the instant 
case, it is desired that the flurosilicone process aids be utilized 
although the process aids disclosed below may be utilized for such 
flurosilicone diorganopolysiloxane polymers with some advantage. 
There is also employed in the present composition 1 to 25 percent and 
preferably 5 to 15 percent by weight based on the polydiorganosiloxane gum 
of a process aid for preventing the gum and the filler mixture from 
structuring prior to curing and after compounding. One example of such a 
process aid is a compound of the formula, 
##STR4## 
where R is a member selected from the class consisting of methyl and 
phenyl, X is a member selected from the class consisting of --OH, 
--NH.sub.2 or --OR', where R' is methyl or ethyl, n has a value of from 2 
to 4, inclusive, and be is a whole number equal to from 0 to 10, 
inclusive. Further details as to the properties, as well as the method of 
preparation of the compound of formula (3), are to be found in the 
disclosure of Martellock U.S. Pat. No. 3,464,945 which is herein 
incorporated by reference. 
The process aid may also be a dihydrocarbon-substituted polysiloxane oil 
having a hydrocarbon substituted to silicon atom ratio of from 1.6 to 2.0 
and whose hydrocarbon substituents comprise at least one member selected 
from the class consisting of methyl, ethyl, vinyl, allyl, cyclohexenyl and 
phenyl groups, said polysiloxane oil comprising polysiloxane molecules 
containing an average of from one to two lower alkoxy groups bonded to 
each of the terminal silicon atoms where the alkoxy groups are selected 
from the class consisting of methoxy, ethoxy, propoxy and butoxy. 
Preparation of the alkoxy-containing hydrocarbon-substituted polysiloxane 
oils that can be employed as a process aid in the present invention can be 
carried out by producing one or more types of cyclic 
dihydrocarbon-substituted polysiloxanes from one or more types of 
dihydrocarbon-substituted dichlorosilanes and dialkoxysilanes in 
accordance with the hydrolysis, depolymerization and fractional 
distillation procedures described in detail above with reference to the 
preparation of the gum of formula (1). Then one or more types of cyclic 
siloxanes so produced are mixed with predetermined amounts of a 
dihydrocarbon-substituted dialkoxysilane and the mixture is subjected to 
an equilibration treatment under controlled conditions to produce the 
desired alkoxy end-blocked hydrocarbon-substituted linear polysiloxane 
oil. 
The alkoxy-containing hydrocarbon-substituted polysiloxane oils suitable 
for use in the present invention are relatively low molecular weight 
polysiloxane oils whose polymer chains have at least four and as much as 
35 and more dihydrocarbon siloxy units per molecule. The polysiloxane oils 
preferably have an average of at least one and not more than two alkoxy 
groups bonded to each of the terminal silicon atoms of the molecule. A 
more detailed disclosure of the alkoxy end-blocked polysiloxane process 
aids, as well as their method of preparation, is to be found in the 
disclosure of Fekete, U.S. Pat. No. 2,954,357 which is hereby incorporated 
into this specification by reference. 
There may also be used as a process aid hydroxylated organosilanes which 
contain from one silicon-bonded hydroxyl per 70 silicon atoms to two 
silicon-bonded hydroxyls per silicon atom and contains from 1.9 to 2.1 
hydrocarbon radicals per silicon atom. The remaining valences of the 
silicon atom are satisfied by oxygen atoms. The hydroxylated materials 
include both monomers such as diphenylsilanediol and polymeric materials 
which contain two silicon-bonded OH groups in the molecule. In addition, 
the hydroxylated organosilane may be a mixture of hydroxyl-containing 
siloxanes and completely condensed siloxanes. Irrespective of the 
particular composition of the hydroxylated organosiloxane, it is necessary 
that there by present in said organosiloxane from one OH to 70 silicon 
atoms to two OH per silicon atom. 
The hydroxylated siloxanes may be prepared by any suitable method, such as 
heating said siloxanes with steam under pressure at temperatures of about 
120.degree. C. or hydrolyzing silanes of the formula R.sub.n SiX.sub.4-n 
where X is any hydrolyzable group such as Cl, OR, H, --OOR and R is a 
monovalent hydrocarbon radical. The former method is preferred for the 
preparation of those hydroxylated materials in which the hydrocarbon 
radicals are alkyl, while the latter method is best for the siloxanes in 
which hydrocarbon radicals are monocyclicaryl hydrocarbon radicals. 
Further, detailed information as to the hydroxylated organosiloxanes which 
may be used as process aids is to be found in Knokle et al U.S. Pat. No. 
2,890,188, the disclosure of which is being incorporated into this 
application by reference. 
Any of the above process aids may be used alone or mixtures thereof may be 
used in the above-defined concentrations. Further, other suitable process 
aids may also be used in the silicon rubber compositions of the present 
invention. Such ingredients are, for instance, disclosed as common in 
Glaister U.S. Pat. No. 3,933,726 which is incorporated into the parent 
case by reference. 
Generally such process aids are added to the diorganopolysiloxane polymer 
to mix the filler into the polymer which mixing is usually carried out in 
a dough-mixer. It is preferred to utilize a process aid in the invention 
of the instant case so as to mix the filler into the diorganopolysiloxane 
polymer with facility and also so as to prevent structuring of the 
composition prior to cure. The above forms the basic composition of the 
instant case with minus of course the antistatic dissipating compound of 
the instant case. In addition, other ingredients may be utilized in the 
above composition as is well known in the heat vulcanizable silicone 
rubber composition art such as pigments, such as heat agent additives, 
such as structure controlling additives, such as compression set 
additives, such as oil resistant additives. For instance, there may be 
incorporated in the above composition, a small quantity of magnesium oxide 
to increase the solvent resistance of the composition. With respect to the 
diorganopolysiloxane base polymer, it is preferred that the organo groups 
in one instance be selected from methyl, phenyl and vinyl. 
Accordingly, for maximum static dissipating properties, it is desired that 
the diorganopolysiloxane polymer generally contain anywhere from 0.002 to 
0.5 weight percent of vinyl groups and more preferably from 0.002 to 0.2 
weight percent of vinyl groups. In addition, for maximum static 
dissipating properties desired that the diorganopolysiloxane polymer may 
have anywhere from 1 to 10 weight percent of phenyl substituent groups and 
more preferably from 1 to 5 weight percent of phenyl groups. 
Finally, in the compositions of the instant case, there must be present the 
static dissipating polyether polysiloxane copolymers of the instant case. 
As set forth above, broadly the polyether polysiloxane copolymer additive 
of the instant case may have the formula A.sub.W.B.sub.V where A is the 
polysiloxane moiety and B is the polyether moiety where broadly W is a 
whole number varying from 1 to 100 and B is a whole number varying from 1 
to 200. Such copolymers are well known in the art. 
Generally there may be utilized from 0.1 to 1.5 parts by weight of the 
polyether polysiloxane copolymer and more preferably 0.25 to 0.7 parts by 
weight of the polyether polysiloxane copolymer per hundred parts of the 
diorganopolysiloxane base polymer. The polyether moiety may be appended to 
the polysiloxane moiety in any convenient fashion. For instance, the 
linkage may be Si--O--C, 
##STR5## 
or Si (CH.sub.2).sub.t where t varies from 2 to 20. It should be noted 
that the Si--O--C linkage is not preferred since such a linkage is 
unstable to water and water will cause the bond to break. The other two 
linkages, are more preferred since they are more resistant to hydrolytic 
degradation. It should be noted that such materials are well known for a 
surfactant for polyurethane foams and there are many examples of them. As 
far as is known, most of such polyether polysiloxane copolymers will 
function in the inventions in the compositions of the instant case to act 
as static dissipating additives to heat curable silicone rubber 
compositions. It should be noted that the polyether moiety in the 
polyether polysiloxane copolymers of the instant case, may be composed of 
only ethylene oxide units or can be composed of ethylene oxide and 
propylene oxide units or be composed of ethylene oxide, propylene oxide 
and butylene oxide units or be composed of ethylene oxide and butylene 
oxide units. 
The more preferred polyether polysiloxane additives for use in the instant 
invention is one having the formula, 
##STR6## 
where R and R' are monovalent hydrocarbon radicals of less than 8 carbon 
atoms R.sup.2 is selected from alkylene and aryl radicals of up to 20 
carbon atoms; n is an integer that varies from 2 to 4; x varies from 5 to 
30; for the case n is equal to 2 and x varies from 1 to 40 for the case n 
equals to 3 or 4 where there may be ether units with n equals to 2, 3 and 
4 in the same molecule; a is a whole number that varies from 1.51 to 1.99 
and b varies from 0.019 to 0.45 the sum of a + b varies from 2.012 to 2.1. 
Such polysiloxane polyether copolymers are for instance, disclosed in 
Moeller U.S.P. 3,965,150 which disclosure is incorporated in the present 
case by reference. Another polyether polysiloxane additive which is 
preferred in the invention of the instant case is one having the formula, 
##STR7## 
where R.sup.6 and R.sup.3 are monovalent hydrocarbon radicals, R.sup.4 is 
a lower alkyl radical, 1 to 8 carbon atoms u has a value of at least 2, p 
has a value from 2 to 3, inclusive, q has a value from 2 to 4, inclusive 
and s has a value of at least 5. Disclosure of such compounds as well as 
their method of preparation is set forth in Holdstock U.S. Pat. No. 
3,629,165 which is incorporated into the present case, by reference. 
Examples of other patents that refer to such polyether polysiloxane 
polymers and their method of preparation are for instance Bailey and 
O'Connor U.S. Pat. Nos. 2,834,748 and 2,917,480; Bailey 2,970,15 and 
3,507,815; Morehouse 3,505,377 and Morehouse United Kingdom Pat. No. 
1,088,493 and French Pat. No. 1,550,037. In addition, there is United 
Kingdom Pat. No. 1,149,744, Netherland Pat. No. 6,601,308 and U.S. Pat. 
Nos. 3,168,543 as well as Raleigh 3,654,195. All of these patents are 
incorporated into the present case by reference. It should be noted that 
the invention of these polymers is not the invention of the instant case. 
There are other examples of patents of such polyether polysiloxane 
copolymers; however, to recite all of them would unduly prolong the 
instant specification. Suffice to state that as far is known all such 
polyether polysiloxane copolymers function as static dissipating additives 
in the invention of the instant case. It should be noted that the 
invention of the instant case does not lie in the preparation of such 
polyether polysiloxane copolymers but lies in their use in a heat curable 
silicone rubber composition to produce static dissipating heat curable 
silicone rubber composition that is not totally conductive. The 
preparation of the SiO--C linkage polyether polysiloxane copolymer is well 
known in the art. Briefly, alkoxylated polysiloxane is reacted with a 
hydroxy terminated polyether to produce the desired copolymer. For the 
Si(CH.sub.2).sub.t linkage the most convenient preparation seems to be the 
reaction of a hydrogen containing polysiloxane with an olefinic containing 
polyether in presence of a platinum catalyst. This method can also be used 
in the production of those polyether polysiloxane copolymers in which the 
linkage is 
##STR8## 
where t is defined previously. Such polyether polysiloxane copolymers may 
also be prepared by reacting an olefinic containing acid with a polyether 
containing a hydroxl group and then reacting the resultant olefinic 
polyether compound with a hydrogen polysiloxane with the hydrogen groups 
in the desired location in the polysiloxane chain to produce the desired 
polyether polysiloxane copolymer which is the static dissipating additive 
of the instant case. 
It should be noted that the polyether groups need not be appended to the 
linear end of a polysiloxane chain. The polyether groups may be appended 
either to one terminal position of the polysiloxane chain or they may be 
appended on both terminal positions of a linear polysiloxane chain. In 
addition the polyether groups can be appended to the silicone atoms in the 
polysiloxane/chain as well as to silicone atoms at both the terminal 
positions of the polysiloxane chain. In addition, there may be utilized as 
a static dissipating additive in the compositions of the instant case a 
compound where the polyether is appended to the silicone atoms at the ends 
of polysiloxane chain which polysiloxane chain emanates from a 
trifunctional silicone atom, as disclosed in the foregoing Holdstock U.S. 
Pat. No. 3,629,165. These compounds may be obtained by reacting a hydrogen 
polysiloxane to add on the olefinic polyether group to the hydrogen atom 
of a polysiloxane polymer to produce the copolymer which reaction is well 
known. For instance, various polyethers may be reacted together and in 
addition with an olefinic alcohol or olefinic acid to produce the desired 
olefinic polyether moiety. The resulting olefinic polyether moiety may 
then be reacted with a hydrogen polysiloxane in the presence of platinum 
catalyst to produce the desired polyether polysiloxane copolymer. Alkoxy 
containing polysiloxanes or hydrogen containing polysiloxanes can be 
prepared by methods well known in the art. Briefly, such methods comprise 
equilibrating cyclic-tetrasiloxanes having hydrogen alkoxy groups in them 
in the presence of a mild acid such as toluene sulfonic acid at 
temperatures in the range of 100.degree. to 200.degree. C., in the 
presence of the appropriate amount of chainstoppers, the chainstoppers 
that may be used are alkoxy or hydrogen containing chainstoppers as is 
desired to produce the desired hydrogen containing polysiloxane within the 
scope of the instant case or to produce the alkoxy containing polysiloxane 
within the scope of the instant case. Accordingly, after the hydrogen 
polysiloxane or alkoxy containing polysiloxane which may have a viscosity 
of anywhere from 50 to 500,000 centipoise at 25.degree. C. is equilibrated 
in the presence of a mild acid such as toluene sulfonic acid or acid 
activated clay such as filtrol sold by Filtrol Corporation of Los Angeles, 
California, the equilibration reaction is terminated. The acid is 
neutralized with a mild base and the cyclics are vented off to give the 
desired hydrogen polysiloxane or alkoxy containing polysiloxane. 
This material is ready to be utilized in a SiH olefin reaction to react 
with the olefinic polyether in the presence of a platinum catalyst to 
produce desired polyether polysiloxane copolymers which can be utilized as 
static dissipating ingredient in the invention of the instant case. As 
stated previously hydride containing chainstoppers may be utilized so as 
to produce hydride terminated hydrogen polysiloxanes which when reacted 
with olefinic polyether would result in polyether groups being appended to 
terminal positions of the polysiloxane chain. Such hydrogen polysiloxane 
may also be reacted with alcohol to impart alkoxy group to the 
polysiloxane as such so that it can react with a polyether to produce the 
foregoing polyether polysiloxane copolymers with an SiOC linkage. Such a 
reaction is preferred to produce the alkoxy containing polysiloxanes since 
alkoxy-containing cyclictetrasiloxanes are equilibrated with difficulty 
such as to arrive at a polysiloxane polymer having the desired alkoxy 
substituent groups intact after the equilibration procedure. The 
equilibration procedure is much the same that was utilized to produce the 
diorganopolysiloxane polymer, the main difference being in the use of an 
acidic catalyst for the equilibration procedure versus a basic catalyst 
such as potassium hydroxide with the equilibration procedure of the 
diorganopolysiloxane polymer. Briefly, the catalyst, whether it be an acid 
catalyst or alkali metal hydroxide catalyst in equilibration procedure 
should be utilized at a concentration of anywhere from 5 to 500 parts per 
million. The cyclic tetra siloxanes containing alkoxy groups or hydride 
groups may be obtained by the hydrolysis of the appropriate halosilanes 
and then the cracking of the hydrolyzate with a basic catalyst to 
preferentially distill overhead and separate in a fairly pure form the 
appropriate hydrogen cyclictetrasiloxanes or alkoxy containing 
cyclictetrasiloxanes. For more information as to the preparation of such 
polyether polysiloxane copolymers reference is made to the foregoing 
patents discussed above which are incorporated into the present case by 
reference and specifically, the Moeller U.S. Pat. Nos. 3,965,150, 
Holdstock 3,629,165. 
Another procedure for preparing the polyether polysiloxane copolymers 
having a carbonyl linkage is by equilibrating at elevated temperatures the 
appropriate cyclictetrasiloxanes containing cyanoalkyl substituent groups. 
After the equilibration procedure is terminated wherein about 85% of the 
cyclictetrasiloxanes have been converted to the linear polymer, the acidic 
catalyst is neutralized and the excess cyclics are vented off to leave 
behind the desired cyanoalkyl substituted linear polysiloxane. The 
resulting polysiloxane is then reacted with water in the presence of 
strong acid such as hydrochloric acid to convert the cyano group to 
carboxylic acid groups. The carboxylic acid substituted linear 
polysiloxane with the desired substituted of carboxylic acid groups is 
then reacted with a hydroxy terminated polyether to result in the desired 
polyether polysiloxane copolymer having carbonyl linkages. There are other 
examples of preparation of such compounds which will not be gone into 
here, the above description being given as examplary. Suffice to state 
that the preparation of such polyether polysiloxane copolymers is well 
known in the art to produce the desired copolymer and such copolymers may 
be utilized in the concentrations disclosed above to produce the desired 
static electricity dissipating heat curable silicone rubber composition. 
It should also be noted that it is possible and there can be utilized as a 
static dissipating additive in the invention a polyether polysiloxane 
copolymer in which the polyether moieties are appended only to the 
internal silicone atom in the internal part of the polysiloxane chain. The 
polyether polysiloxane copolymers of the instant case may be added in any 
order to produce the heat curable silicone rubber compositions. The order 
of mixing the ingredients is not important. Preferably, it is desired that 
the filler treated or untreated be added to the polysiloxane polymer first 
with the process aid and the filler incorporated into the 
diorganopolysiloxane polymer in a dough mixer or in similar apparatus to 
form a uniform mixture. At that time it is desired to add the other 
additives and also to add the static dissipating additive of the instant 
case. the peroxide curing catalyst is preferably added last or milled into 
the composition last prior to the final packaging of the composition. 
After the composition has been molded to the desired part with the 
peroxide curing catalyst, it is simply heated to elevated temperatures at 
temperatures of 100.degree. C. or above to cure the composition to a 
silicone elastomer. However, in spite of the above preferred mixing 
procedure set forth, there may be utilized any procedure in the mixing of 
the ingredients without any detrimental effects. In the instant 
composition there is also another ingredient that may be utilized as the 
preferred additive. Accordingly, there may be added to 100 parts of the 
base diorganopolysiloxane polymer from 1 to 25 parts by weight of a linear 
diorganopolysiloxane polymer having a viscosity of anywhere from 50 to 
50,000 centipoise at 25.degree. C. Such a material may be added to the 
compositions of the instant case as a diluent to enhance the mixture of 
the ingredients and to also aid in the static dissipating properties of 
the cured elastomer. Preferably the organo groups of such linear 
diorganopolysiloxane polymer having a viscosity of anywhere from 50 to 
50,000 centipoise and more preferably having a viscosity of 100 to 10,000 
centipoise at 25.degree. C. are selected from lower alkyl radicals from 1 
to 8 carbon atoms, vinyl radicals and phenyl radicals. Most preferably, 
the organo substituent groups of such low viscosity linear 
diorganopolysiloxane polymer are selected from methyl and vinyl 
substituent groups where the vinyl concentration does not exceed 1 mole 
percent in the composition. Preperation of such polymers is known in the 
art and is essentially the same for the base diorganopolysiloxane polymer 
except that in this case in the equilibration the polymer is catalyzed 
with a mild acid instead of a strong base. 
Such low viscosity diorganopolysiloxane polymer need not be used in the 
composition of the instant case. Previously, other additives may be 
utilized in the compositions of the instant case as long as they do not 
interfere with the static dissipating properties of the additives. It 
should also be noted that the concentration of the static dissipating 
additive of the instant case, will vary from application to application 
depending on the type of ingredients that are present in the composition. 
Generally, as stated previously, per 100 parts of the base 
diorganopolysiloxane polymer there may be utilized from 0.1 to 1.5 parts 
by weight of the static dissipating additive. If more than 1.5 part is 
utilized then such concentration of the static dissipating additive may 
cause improper cure of the composition and affect its physical properties. 
If less than 0.1 parts is utilized, then the static dissipating additive 
does not properly perform its function. It is desired to utilize from 0.2 
to 0.7 parts of the static dissipating additive. This range has been found 
to yield the maximum benefits of static dissipating without detracting 
from the resulting physical properties of cured elastomer. In addition, 
the conjunctions of the instant case provide good bonds to substrates and 
especially metallic substrates such as aluminum or stainless steel with 
the use of primers. 
In the examples below, a very general test was utilized to determine the 
static dissipating properties of the cured elastomer which will herein be 
referred to as the cigarette ash test. Briefly, after the cured 
composition had been formed, a static charge was placed on the composition 
and some cigarette ashes were allowed to fall on the surface of the 
elastomer. If the cigarette ash stuck to the elastomer, then the 
composition did not have sufficient static electricity dissipating 
properties. If the cigarette ash could be easily blown away from the 
surface of the elastomer, then the cured elastomer had the proper static 
electricity dissipating properties. 
The examples below are given for the purpose of illustrating the invention 
of the instant case and not given for the purpose of setting limits and 
boundaries to the scope of the invention. All parts are by weight. 
EXAMPLE #1: 
There was mixed 63 parts of 0.2 mole percent methylvinyl, 5.3 mole percent 
phenylmethyl polysiloxane of a viscosity of 50,000,000 centipoise at 
25.degree. C. To this there was added 37 parts of 5.3 mole percent 
diphenyldimethyltrimethylsiloxy endstopped polysiloxan gum of a viscosity 
of 50,000,000 centipoise at 25.degree. C., 0.25 parts of water 8 parts of 
methoxy endstopped dimethyldiphenylpolysiloxane polymer which was utilized 
as a process aid and which had a viscosity of between 33 to 60 centipoise 
at 25.degree. C. To this there was added 26 parts of a fumed silica 
treated with a cyclic polysiloxane. To this there was added 5.4 parts of a 
dimethyl polysiloxane fluid, as a diluent having trimethyl siloxy 
chainstopping units, and having a viscosity of 20 centipoise at 25.degree. 
C. To this there was added 0.8 parts of polyether polysiloxane copolymer 
of the formula, 
##STR9## 
To this the above composition was then cured with 0.5 parts of dicumyl 
peroxide at 10 minutes at 350.degree. F. plus there was utilized a post 
cure of 4 hours at 400.degree. F. The cured elastomer passed the cigarette 
ash est and had the following physical properties: 
Shore A Durometer pi: 25 
Tensile strength psi: 900 
Elongations: 600% 
Tear, Die B: 80 ppi 
EXAMPLE #2: 
There was prepared a composition containing 100 parts by weight of a 
polymer composed of 0.2 mole percent of methyl vinyl diorganosiloxy units 
5.3 mole percent of diphenylsiloxy units, the rest of the substituent 
groups being dimethyl siloxy groups with triorganosiloxy terminal 
chainstopping units in the polymer. The polymer has a viscosity of 
50,000,000 centipoise at 25.degree. C. To this polymer there was added 1 
part of distilled water; 8 parts by weight of a methoxy dimethyl siloxy 
chainstopped polydimethyldiphenyl siloxane process aid, having a viscosity 
of 33 to 60 centipoise at 25.degree. C., and 26.7 parts of fumed silica 
treated with octylmethylcyclictetrasiloxane. To 100 parts of the above 
mixture there was added 3.6 parts of a trimethyl siloxy endstopped 
dimethyl polysiloxane of 20 centipoise at 25.degree. C. and 0.6 parts of 
the polyether polysiloxane static reducing additive of Example I. Into the 
resulting composition there was milled 0.5 parts of dicumyl peroxide and 
the composition after having been fabricated to a sheet was cured by 
heating the composition for 10 minutes at 350.degree. F. The composition 
was then post-cured for 4 hours at 400.degree. F. so as to stabilize its 
properties. The resulting elastomer sheet passed the cigarette test easily 
and had the following physical properties: 
Shore A Durometer pi: 30 
Tensile strength psi: 1000 
Elongation: 600% 
Tear, Die B ppi: 85