CA1081244A - Silicone fluid curable to hydraulic elastomer - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A silicone fluid is provided herein which is curable to a hydraulic elastomer having a viscosity of 1000 to 1,000,000 centipoises at 25°C. The silicone fluid comprises a copolymer of dimethylsiloxane units with 0.1 to 0.9 percent of methylvinylsiloxane units; the mole percent of methylvinylsiloxane units having a value of (4.8/log V) - C, where V is the viscosity in centipoises and C is a number having a value of from 0.53 to 0.83; the copolymer having end groups selected from the class consisting of trimethylsiloxy, hydroxy and alkoxy with a vinyl-specific peroxide to provide the hydraulic elastomer. Such hydraulic elastomer is characterized by a combination of a high cross-link density and a high proportion of free chain ends. It crumbles to a powder under high shear stress, but has the unique property of flowing like a viscous, fluid through a narrow ofifice. It is useful in hydraulic impact absorbers and other hydraulic systems.

Description

Thi8 invention relates to silicone fluids which are curab~e to hydraulic elastomers.
Thi9 application i8 a division of application Serial No. 208,631 filed Sept. 6, 1974.
Silicone fluids have been used in hydraulic shock sbsorbers be-cause of their ability to dlssipate energy by flowing through an orifice.
They have the disadvantage that they must be used in closed systems to avoid loss by gravity. Even the smallest leak will permit deterioration over a period of time. Nevertheless, up till now no other materials have 10 been found suitable in such application.
It is true that elastomers and other materials have some impact-absorbing ability because of their ability to absorb energy by elastic deformation. It is also true that nost elastomers can be forced through an orifice if sub~ected to enough pressure. In the process, however, pre-, viously known elastomers become so thoroughly degraded that they cannot be used a second time in the same system. The degration is to some extent a mechanical breakdown from the high shear stress involved, but mainly it is chemical degradation caused by the high temperatures generated.
; Silicone elastomers are desirable materials for such an appli-20 cation because oI their high thermal stability. Also they have a high compressibility, which tends to smooth out peaks in the stress-strain :. . .
curve. However, none of those known heretofore have been sui~able. They can be forced through an orifice, thereby being broken down into small particl2s, but these are relatively hard and do not easily flow back into thelr original position. Oil hae been added as a plasticizer to overcome these disadvantages; however, it has not been very successful, since the oil bleeds from the leastomer and eventually leaks out of the system.

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It iB therefore an object of a broad aspect of this inventlon as provided by the present divlsional application to provide a silicone fluid which can be cured to a hydraulic elastomer.
An object of another aspect of this invention as provided by the present divisional application is to provide a silicone fluid which can be cured to a cross-linked silicone elastomer that is easily deformed ~nder pressure and that breaks down into sof~ particles under high shear, such particles having the property or flowing under pressure, but not under the influence of gravity alone.
By one broad aspect of this invention~ a silicone fluid is pro-vided which is curable to a hydraulic elastomer having a viscosity of from 1000 to 1,000,000 centipoises at 25C, the silicone fluid comprising a co-polymer of dimethylsiloxane units with 0.1 to 0.9 mole percent of methyl-vinylsiloxane units; the mole percent of methylvinylsiloxane units having a value of (4.8/log V) - C, where V is the viscosity in centipoises and C
is a number having a value of from 0.53 to 0~83; such copolymer having end groups selected from the class consisting of trimethylsiloxy, hydroxy and alkoxy.
By one variant, the copolymer is repreeented by the formula RO[(CH3)2SiO]x[CH3(C2H3)SiO]yR wherein R is selectcd from the class con-sisting of alkyl radicals of from 1 to 4 carbon atoms, hydrogen and tri-methylsilyl radicals, x is a number of from 270 to 2,700 and y is a number of from O.OOlx to O.OO9x, By another variant, the copolymer contains trimethylsiloxy end groups and has a viscosity of from 5000 to 30,000 centipoises.
By another variant, the value of C ls from 0.63 to 0.78.
By a variation thereof, the viscosity is from 10,000 to 15,000 centipoises and the mole percent of methylvinylsiloxane units is spproxi-mately 0.45.

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By a further aspect, the silicQne fluid contains, in addition, 0.1 to 1.5 percent of a curlng agent selected from the class consistlng of tertiiary alkyl peroxides and diperoxy ketals.
By a variant thereof, the amount of curing agent is from 0.3 to 0.8 percent.
By other variants the curing agent is a tertiary alkyl peroxide, e.g., is dlcumyl peroxide, or is bis (t-butylperoxyisopropyl)-ethane9 or is bis-(t-butylperoxyisopropyl)-benzene, or ls a diperoxy ketal, e.g., is 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane.
By another variant, the curing agent has an ultraviolet absor-bance at 240 nanometers that is no greater than at 260 nanometers.
~xamples of silicone fluids that may be formed into the silicone copolymer of aspects of this invention as provided by the present divisional application are linear siloxane copolymers having the general formula R0[(CH3)2siO]x[cH3(c2H3)sio]y in which R is an alkyl radical of from 1 to 4 carbon atoms, hydrogen or a trimethylsilyl radical, x is a number of from 270 to 2,700 and y is a num- -ber of from O.OOlx to O.OO9x. Generally these silicone fluids contain pre-dominantly, dimethylsiloxane units with small amounts of methylvinylsilox-ane units. The end groups may be trimethylsiloxy, hydroxy or alkoxy groups;
however, for optimum visc.osity control~ the trimethylsiloxy groups are preferred.
The molecular weight may vary between 20,000 and 200,000, corres-pondlng with viscosities between 1000 and 1,000,000 centipoises (cp) at 25C.

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~ ~ , , -. . : ~ - -The ~mount of methylvinylsiloxane units may vary from 0.1 to 0.9 mole percent. The optimum amount varies inversely with the rhain length. Specifically, the optimum methylvinylsiloxane content is given by the relation:
"Vinyl" = lOOY = 4 8 V ~ 0-73 (1) Here "vinyl" is mole percent of methylvinylsiloxane, and V is the viscosity in cp. "Vinyl" may be as much as 0.05 mole percent lower or 0.10 mole per cent higher without departing from the optimum range. In mathematical terms, then, the optimum range is given by the relarion "Vi yl" = 4 8 C (2) where C may vary between 0.63 and 0.78. Small departures from the optimum range are permissiblè, but in any case C should be between 0.53 and 0.83.
As indicated above, the viscosity of the fluld that may be ~
formed into the silicone copolymer of aspects of this invention as provided by the present divisional application may be as low as 1000 cp~ However, even with the optimum vinyl content it is found that the ultimate proper-; ties of the cured elastomers are not as good as when the viscosity of the fluid is at least 5000 cp. That is, the hardness of the elastomer and its ~; resistance to flow are below the desired range.
- 20 Good physical properties in the elastomer derived from the sili-~ cone fluid of aspects of this invention as provided by tha present division-,, ~ . .
al application are obtained if the viscosity of the fluid of aspects of this invention as provided by the present divisional application approaches 1,000,000 cp. However, the vlnyl content has to be so low that control of the degree of cross-linking becomes difficult. Furthermore, fluids of aspects of this invention as provided by the present divisional applica-tion with viscosities above 30,000 cp. are difficult to handle. They are too viscous to pour easily and too ," ~

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~ ~38~4 fluid to be handled like a silicone gum, whlch generally has a viscosity of around 30,000,000 ~p.
The preferred range i9 thus between a viscosity of from 5000 cp, with 0.57 mole percent "Vinyl", to 30,000 cp, with 0.34 mole percent "Vinyl".
The optimum range is from 10,000 to 15,000 cp with ~.45 mole percent of methylvinylsiloxane and a molecular weight of 60,000. ~' ; The fluids of an aspect of this invention as provided by the present divisional application may be prepared by any conventional process known ~in the art for preparing silicone polymers, e.g., condensation of short-chain hydroxy-terminal polymers, acid-catalyzed~equilibration and base-catalyzed equilibration. In a base-catalyzed equilibration a mixture of cyclic oligomers of dimethylsiloxane, cyclic oligomers containing methyl-vinylsiloxane, alone or in combination with dimethylsiloxane, and a short- -~
chain siloxane containing trimethylsiloxy ena groups is heated to a tempera-ture of from 80 to 90C. with fugitive catalyst e.g., tetramethylammonium hydroxide. After 1 to 2 hours the temperature is increased to 130 to 150C.
to destroy the catalyst. If desired, volatile by-products can then be re-moved by further heating under vacuum. The tetramethylammonium siloxano-late described in United States Patent No. 3,433,765 issued March 18, 1969 to L.E. Geipel is an excellent fugitive catalyst for the equilibration.
The choice of peroxide used for curing to provide the hydraulic elastomer of an aspect of the invention of another copending Canadian divi-sional application of Canadian Application Serial No. 208,631 filed Sep-tember 6, 1974, and filed concurrently herewith is important. Peroxides that generate acyloxy radicals, especially diacyl peroxides, such as, for example, benzoyl peroxide, are relatively undersirable because they are strong hydrogen abstractors. The degree of cross-linking is determined - largely by the amount of peroxide and the temperature employed in the vulcanization.
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Vinyl-speciflc peroxides, on the other hand, eenerate cross-links through the vinyl groups, and the degree of cross-linking depends primarily on the number of vinyl groups. Vinyl-specific peroxides are characterized by the fact that their initial decomposltion products are principally tertiary alkoxy radicals.
One class of vinyl-specific peroxides consists of tertiary alkyl peroxides, The simplest members of this class, e.g., tertiary butyl per-oxide and tertiary amyl peroxide, are chemically satisfactory but too vola-tile for long-term storage. Thus it is desirable to usc peroxides having very low volatility at room temperature. For this reason it is preferred that the molecules have at least 14 carbon atoms, for example, as in di-cumyl peroxide.
Peroxides with two or more peroxy groups are often preferred.
These include peroxides such as, for example, bis-(t-butylperoxyisopropyl)-benzene, bis-(t-butylperoxisopropyl)-ethane, and bis-(t-butylperoxyiso-propyl)-acetylene, These are tertiary alkyl peroxides in the sense that every peroxidic oxygen atom i5 attached to a tertiary atom.
Another class of suitable vinyl-specific peroxides may be de9~
cribed as diperoxy ketals. Suitable examples of these are l,l-di-t-butyl-; 20 peroxy-3,3,5-trimethylcyclohexane and n-butyl 4,4-di-t-butylperoxy-~,j valerate.
! All of the specific peroxides enumerated above, as well as other tertiary alkyl peroxides and disperoxy ketals~ may be used to provide the hydraulic elastomer of an aspect of the invention of another copending Canadian divisional application of Canadian application Serial No. 208,631 filed September 6, 1974, and filed concurrently herewith. Bis-(t-butyl-peroxyisopropyl)-benzene (mixed metal and para isomers) has a particular advantage in that its activity is easily monitored by ultraviolet absorption.
It has a characteristic absorption peak at 260 nm, (nanometers) with a : . 1 . ~

minlmum 240 nm. Its decompositlon product8 have an intense absorption at 240 nm, so that it is pogsible to detect a very small amount of decomposi-tion. Some commercial materials that are not visibly decomposed contaln enough of these products to obscure completely all peaks in the range of 230 to 260 nm.
Impure samples of this peroxide are easily purifled by recry-stallization at temperatures at or above 0C. Stlll higher temperatures may be used if up to 10 percent of water is present. Generally one re- ~ -crystallization is sufficient. The product is sa~isfactorily pure if the absorbance at 240 nm is no stronger than the absorbance at 260 nm.
As indicated above the amount of peroxide used is not critical.
Depending somewhat on the equivalent weight of the peroxide, as little as 0.1 percent or as much as 1~5 percent may be used. The preferred range is from 0.3 to 0.8 percent and more preferably 0.5 percent.
These peroxides are all readily soluble in vinyl-containing sili-cone fluids and are stable enough that the solutions may be stored for ; many months at room temperature without decomposition. In the case of nor-mally solid peroxides it is somewhat desirable to preheat the silicone fluid to 50C. to facilitate dissolution.
In order to cure the silicone fluid to provide the hydraulic elastomer of an aspect of the invention of another divisional application of Serial No. 208,631 filed Sept. 6, 1974, and filed concurrently here-with, it i8 heated with the peroxide for a length of time and at a temr perature appropriate to the peroxide. Mlnimum cures require a time equal to at least one half-life of the peroxide. Better results are obtained after 2 or 3 half-lives, and full cures require at least 5 to 10 balf-lives. Longer heating will not cause any bad effects because the silicones -~
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temperatures above 200~C., and the preferred peroxides do not generate acidlc by-products. To avoid excessively long cure times, however, it is desirable to choose a temperature such that the half-life is of the order of one to ten minutes. For example, temperatures of 150 to 180C. for the tertiary alkyl peroxides and 130C. for the diperoxy ketals is satisfac-tory.
The table below illustrates suitable cure times.

Approx.
Temp. Half-life, Time, Peroxide C. Minutes Minutes 10 l,l-Di-t-butylperoxy-

3,3,5-trimethylcyclohexane 140 1 30 Dicumyl peroxide 170 1.5 15 Bis-(t-butylperoxyisopropyl)-benzene 170 3 30 Bis-(t-butylperoxyisopropyl)-benzene 180 1 10 ; Bis-(t-butylperoxyisopropyl)-ethane 175 1 15 It should be noted that the terms "preferred range" and "opti-mum range", in reference to the viscosity and vinyl content of the fluid of aspects of this invention as provided by the present divisionly appli-cation, are used with a particular application in mind, i.e. an impact - absorber similar to those described in Unitea States Patents 3,053,526 2~
issued September 11, 1962 and 3,178,037 issued April 13, 1965 to Kendall.
It should be pointed out, however, that the hydraulic elastomers of an aspect of the invention of another copending Canadian divisional applica-tion of Canadian application Serial No. 208,831 filed September 6, 1974, and filed concurrently herewith are useful in a great variety of hy-draulic devices. Examples include shock absorbers, fluid couplings, break-ing systems, vibration dampers, rate-control devices and ~any others. The same elastomers work well in each of these. In some applications the opti-mum range of usuable fluids of aspects of this invention as provided by the present divisional application may be slightly different from those ~':

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described above. In almost all cases, however, it will be found that the optimum range will lie within the boundaries of the preferred range given above~ That is, the viscosity of the fluid of aspects of this invention as provided by the present divisional application will lie between 5000 and 30,000 cp and the value of C in equation (2) will lie between 0.53 and 0.83.
Ideally each hydraulic elastomer of an aspect of tha invention of another copending Canadian divisional application of Canadian application -Serial No. 208,631 filed Sept. 6, 1974, and filed concurrently herewith -~
should be tested in the device for which it is designed. In cases where this is impractical the following laboratory test was devised, based on a -Brabender P~ASTI-CORDER (Trade Mark of an instrument of C.S. ~rabender In-struments, Inc., 50 East Wesley Street, South Hackensack, New Jersey). The measuring head used in Type 6/115 volts/114 amp., No. 105, with roller blades. It is preheated to the curing temperature, 350F., with the rollers turning at 50 rpm, and the uncured fluid-containing peroxide is introduced ~by means of a hand extruder known by the Trade Mark of SEMC0. A small ex-:' .
cess is used to make sure that the cavity is full. The cure is foilowed by means of a torquemeter. The torque starts to increase noticeably after 3 minutes. Very shortly thereafter a gel point is reached and the material turns into a fine powder. The torque continues to rise3 however, and fin-ally levels off after 10 to 20 minutes. During this time the powder flows around the blades like an extremely viscous liquid. The shear stress is believed to be very similar to that in the actual hydraulic impact absorber.
At any rate an elastomer with the right hardness that shows a torque of oon to 1550 meter-grams will perform well in an impact absorber.
Regardless of the nature of the shearing mechanism the fluid-like properties develop as the hydraulic elastomer of an aspect of the invention of ano~her ropending Canadian divisional application of Canadian application Serial No. 208,63I filed September 6, 1974, and filed concurrently herewith -is broken down into small particles. The size ~ 9 ~ :, :: . . . , . - : ~

of the particl~s is not critical, but for optimum reproducibility they should be less than one illimeter ln diameter.
Hardness i9 determined wlth a Shore A durometer on 1/4 inch but-tons cured, typically, for 25 minutes at 350F. (ASTMD-395 Method B). Op-timum results are obtained if the Shore A hardness is between 11 and 14.
Under certain conditions fairly good results may be obtained with elasto-mers that have a Shore A hardness as low as 9 or as high as 16.
In addition to the physical characteristics of hardness and flow behaviour, the cured hydràulic elastomer of ~n aspect of the invention of 10 another copending Canadian divisional application of Canadian application Serial No. 208,631 filed Sept. 6, 1974, and filed concurrently herewith may be characterized chemically. It contains an unusually large number of free ends, i.e., terminal segments that are not involved in the cross-lin~ing process. Given a fluid of aspects of this invention as provided by the present divisional application in the molecular weight range of 20,000 and given that there are two end groups per molecule, the number of end groups can be calculated as lying between 0.074 and 0.74 per 100 silicon atoms.
In the preferred range the number of free end lies between 0.18 and 0.34 per 100 silicon atoms. The optimum fluid molecule, with a molecular weight 20 of 60,000 has 0.25 end groups per 100 silicon atoms; this figure remains essentially unchanged on curing. In the cured elastomer the average length of the free ends is between 50 and 100 silicon atoms.
By contrast, a typical silicone gum molecule, with a molecular weight of around 500,000 has only 0.03 end groups per 100 silicon atoms.
The free end groups in the hydraulic elastomers of an aspect of the inven-tion of another copending Canadian divisional application of Canadian appli-cation Serial No. 208,631 filed Sept 6, 1974, and flled concurrently here-with are believed to have a plasticizing effect that is important in de-termining the physical properties of the elastomer.

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~ he cured hydraulic elastomer of an aspect of the invention of another copending Canadian divisional application of Canadian application Serial No. 208,631 filed Sept. 6, 1974, and filed concurrently herewith, particularly one made from the preferred range of fluids of aspects of this invention as provided by the present divisional application, is further characterized by a relatively high cross-link density. There is normally at least one three-carbon cross-link per original vinyl group. This is true whether curing takes place by repeated free-radical-initiated vinyl addition reactions or by alternating chain-transfer-to-methyl and vinyl addition. More cross-links form, especially in fluids o~ aspects of this invention as provided by the present divisional application of low vinyl content, by chain-terminating coupling reactionsO Neglecting those formed by coupling, the effective cross-link density is given by`the expression C.D. = "Vinyl" - E.G./2 (3) where C.D. is the number of cross-links per 100 silicon atoms, "Vinyl" is the original number of vinyl groups per 100 silicon atoms, and E.G. is the number of end groups per 100 silicon atoms. The reason for the last term is that two end groups in effect counteract one cross-link.
The hydraulic elastomer of an aspect of the invention of another ~ 20 copending Canadian divisional application of Canadian application Serial `~ No. 208,631 filed September 6, 1974, and filed concurrently herewith made from the optimum fluid of aspects of this invention as provided by the present divisional application is thus calculated to have a minimum cross-link density of 0.45 - 0.25/2 or 0.325 cross-links per 100 silicon atoms.
The preferred range of fluids of aspects of this invention as provided by the yresent divisional application gives minimum .,~ .

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Allowing for some cross-links due to coupling, the preferred range of cross-llnk density is from 0.25 to 0.50 cross-links per 100 silicon atoms.
A typical "prior art" silicone elastomer made from a gum having 0.1 to 0,2 mole percent vinyl has a calculated minimum cross-link density of between 0.098 and 0.198. The novelty of the present elastomers does not reside solely in their high cross-link density, however, but in the combination of high cross-link density and high fr~e end density~
Various embodiments of this invention are further illustrated in the followlng examples, in which all parts are by weight unless other-wise specified.

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A mixture containing lO0 parts of octamethylcyclotetrasilo~ane, 0.52 part of mixed cyclic methylvinylsiloxanes obtained from the hydrolysis product of methylvinyldichlorosilane, and 1.46 parts of a short-chain trimethylsilyl-endblocked polydimethylsiloxane having an average of 8.15 silicon atoms per molecule (endblocked), is heated to 85C. To this is added 0.21 part of a tetramethylammonium siloxanolate solution containing the equivalent of 6.2 percent of tetramethylammonium hydroxide. The viscosity of the mixture begins to increase in a few minutes and equilibra-tion is complete in one hour at 85C. The temperature is then raised to 140C. to destroy the catalyst. The product is then stripped for an hour under vacuum to remove a small amount of volatile matter, consisting pri-marily of an equilibrium quantity of cyclic siloxanes. The product con-tains 0.45 mole percent of methylvinylsiloxane units, which essentially the same as in the initial mixture. It is a clear fluid with a viscosity of 12,000 cp at 25C.

An impure lot of bis-(t-butylperoxyisopropyl)-benzene, mixed meta and para isomers, having almost complete ultraviolet absorption in the range of 230 to 260 nm at a concentration of 0.08 percent in heptane, `~ ls purified in the following manner. It i9 dissolved in warm methanol and water to give a solution containing 15 parts of the peroxide, 80 parts of methanol and 5 parts of water. The solution is cooled slowly to room temperature and then to 0C., and held a~ 0C. to complete the recrystal-lization. It is then filtered through a Buchner funnel. The filter cake ; thus obtained is substantially dry, containing no mo~è than lO percent of water and methanol. It is crushed and finally dried in a stream of nltro-gen, giving a yield of recovered peroxide of 75 percent. The recrystal-lized material, when diluted to 0.08 percent in heptane, shows an 80 per-'', ~ .
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cent absorbance at 260 mn and a 65 percent absorbance at 240 nm. Although the peroxide is of a pale buff color, the U.V. absorption is not signi~i-cantly different from that of a pure white maLerial obtained by :, 'J

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repeated crystallization. This once-recrystalli~ed material will be re-ferred to as "the peroxide of Example 2".
EXAMPLE_3 One hundred parts of the fluid of Example 1 is heated to 55C.
To this is added one half part of the peroxide of Exampl~ 2. It dissolves quickly and does not recry-tallize on cooling. U.V. absorption shows no decomposition of the peroxide. A portion of the mixture is poured into the cavity of an impact absorber. The assembly is then heated for 30 min-utes in an oven at 450F., the internal temperature reaching a maximum of 410F. This is sufficient for complete cure of the fluid to a soft elasto-mer. The assembly is then placed in a dynamometer and subjected to repeated compression-retraction cycles, in which the test sample is allowed to cool to room temperature between cycles. The amplitude is such that virtually all of the elastomer is forced through the orifice in the first stroke, thereby being broken into fine particles. The particles will flow back during the retraction phase. The stress-strain curve is virtually the same for all compression-retraction cycles except the~first, indicating that there is no further chemical or mechanical breakdown of the elastomer.
In each cycle, the energy ab~orption ls sufficient ~o absorb an impact of 2000 ioules without ''bottoming out" or transmitting an excessive force at any time during the cycle.
Another portion of the mi~ture is placed in the mixing head of the Brabender PiASTI-CORDER de8cribed above, which has been preheated to 350F. A sharp rise ln torque occurs after 3 minutes, reaching 1200 meter-grams in 7 minutes, and finally levelling off at 1350 meter-grams in less than 20 minutes. When cool, the elastomer is found to be in the form of a soft white powder. This can be compressed by hand into a transparent mass with the appearance of a llquid, but on release of pressure it reverts to the powder, thus proving it to ~e fully cured.

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A third portion is cured for 25 mlnutes at 350F. in the form of a l-inch by 1/4-inch but~on and tested with the Shore A duro~eter. It 11 a - . ~.
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EXAMPLES 4 to 15 Fluids are prepared ln accordance with ths procedure of ~xample 1, except that the amounts of cyclic methylvinylsiloxane and endblocker are varied to give di~ferent viscosities and vinyl contents. After strip-ping samples are heated in a vacuum oven and found, by weight loss, to con-tain between 2.3 and 4.2 percent of residual volatile matter, which is an acceptable range. The fluid of Example 15 is the most difficult to strip) because of its relatively high viscosity, and has the highest residual vola-tiles. Each fluid is mixed with 0.5 percent of the peroxide of Example 2and cured at 350F. in accordance with Example 3. The results of the tests are illustrated in the following table.

Mole Brabender Example Viscosity, Percent Test, Shore A
` No. cP "Vinyl" Meter-gramsHardness 4 ~,ooo 0.75* 900 10

5,400 0.50 1250 11 " 6 5,230 0.55 1275 12 7 5,100 0.65 1250 14 . .
8 8,~80 0.35* 1175 8 9 10,500 0.40 1300 11 20 3 12,000 0.45 1350 12 12,400 0.55 1350 15 11 10,700 0.65* 1400 19 12 11,000 0.80* 1~00 22 13 13,600 l.00* 1300 26 14 19,000 0.45 1450 13 25,700 0.45 1300 13 It can be seen that all fluids that fall wi~hin the optimum range of vinyl content as defined above, give satisfactory results, i.e.

i~ Brabender values between 1000 and 1550, and Shore A hardness between 9 and ' ~ ' : :. ,,:: . . ~ - . ~ -: . -~: :. - : ~ : : . : . : : .
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15; all but.one, No. 10, fall in the optimum range of hardness, 11 to 14.
All those that are outslde the optimum range of vinyl content, .

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A fluid havlng a viscosity of 87,000 cp and 0.20 mole percent "Vinyl" i8 cured in the Brabender Plasti-corder at 350F. in accordance with Example 3 and gives a final torque of 1200 meter-grams which ~s acceptable.
EXAMPLES 17 to 22 A fluid having a viscosity of 140,000 cp and 0.14 mole percent l~ "Vinyl" is cured in the Brabender Plasti-Corder with various amounts of peroxide and at various temperatures as shown in the following table.

- ExamplePeroxide, d Cure Temperature ~ :: Torque, No. Percent F. Meter-g~ams 17 0.5 350 1300 18 0.75 35~ 1350 19 0.95 350 1300 `
1.15 350 1300 21 0.5 400 1425 `
22 0.5 450 1600 It is apparent that increasing the peroxide level has little effect on the final torque. On the other handSvery high curing tempera-tures are undesirable, as indicated by the high torque`value in Example 22.
EXAMPLES 23 to 26 Example 3 is repeated except that 0.5 percent o the ~ollowing catalysts are used:
; Impure bis-(t-butylperoxyisopropyl)-benzene (20 minutes at 350F) Di-t-butylperoxy-3~3~5-trimethylcyclohexane (30 minutes at 285F.) Dicumyl peroxide ~15 minutes at 340F.) Bis-(t-butylperoxyisopropyl)-ethane (20 minutes at 350F.) : i .

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In all cases the Brabender torque is between 1300-1400 meter-grams, and the cured elastomers are indi~tingtlishable in appearance and mechanical properties from that obtained in Example 3.

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Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A silicone fluid curable to a hydraulic elastomer, having a viscosity of from 1000 to 1,000,000 centipoises at 25°C, comprising a co-polymer of dimethylsiloxane units with 0.1 to 0.9 mole percent of methyl-vinyl siloxane units; the mole percent of methylvinylsiloxane units having a value of (4.8/log V) - C, where V is the viscosity in centipoises and C
is a number having a value of from 0.53 to 0.83; said copolymer having end groups selected from the class consisting of trimethylsiloxy, hydroxy and alkoxy.

2. The silicone fluid of claim 1, wherein the copolymer is represented by the formula RO[CH3)2SiO]x(CH3(C2H3)SiO]yR
wherein R is selected from the class consisting of alkyl radicals of from 1 to 4 carbon atoms, hydrogen and trimethylsilyl radicals, x is a number of from 270 to 2,700 and y is a number of from 0.001x to 0.009x.

3. The silicone fluid of claim 1 wherein the copolymer contains trimethylsiloxy end groups and has a viscosity of from 5000 to 30,000 centipoises.

4. The silicone fluid of claim 1 wherein the value of C is from 0.63 to 0.78.

5. The silicone fluid of claim 2 wherein the viscosity is from 10,000 to 15,000 centipoises and the mole percent of methylvinylsiloxane units is approximately 0.45.

6. The silicone fluid of claim 1 which contains in addition 0.1 to 1.5 percent of a curing agent selected from the class consisting of tertiary alkyl peroxides and diperoxy ketals.

7. The silicone fluid of claim 6 wherein the amount of curing agent is from 0.3 to 0.8 percent.

8. The silicone fluid of claim 6 wherein the curing agent is a tertiary alkyl peroxide.

9. The silicone fluid of claim 8 wherein the curing agent is dicumyl peroxide.

10. The silicone fluid of claim 8 wherein the curing agnet is bis-(t-butylperoxyisopropyl)-ethane.

11. The silicone fluid of claim 8 wherein the curing agent is bis(t-butylperoxyisopropyl)-benzene.

12. The silicone fluid of claim 11 wherein the curing agent has an ultraviolet absorbance at 240 nanometers that is no greater than at 260 nanometers.

13. The silicone fluid of claim 6 wherein the curing agent is a diperoxy ketal.

14. The silicone fluid of claim 13 wherein the curing agent is 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane.