CA1179093A - Heat curable organopolysiloxane compositions - Google Patents

Abstract

Abstract of the Disclosure A curable organopolysiloxane composition is provided having a low viscosity in the uncured state and high physical strength in the cured state. A
mixture of organopolysiloxane having silicone vinyl containing diorganopolysiloxane and silicon hydride containing siloxane is utilized in combination with a halogen containing platinum tetramer. The heat curable liquid injection moldable mixture exhibits an extended shelf life in the absence of an inhibitor at room temperature and rapidly converts to the solid cured state at 150°C.

Description

~.~ 7,'3~ RD-1301~

HEAT CURABLE ORGANOPOLYSILOXANE COMPOSITIONS

Cross Reference to Related Applications Reference is made to the Canadian application of Edward M. Jeram, Serial No. 382,440, filed July 24, 1981, for Addition Curing Silicone Compositions and assigned to the same assignee as the present invention.
Background of the Invention . _ The present invention relates to an addition curing system, and more particularly the present invention relates to heat curable organo polysiloxane compositions having a low viscosity in the uncured state and high physical strength in the cured state~
An example of a platinum catalyzed curable organ-opolysiloxane composition based on the use of a vinyl containing diorganopolysiloxane and a silicon hydride utilizing a platinum catalyst is shown by Modic, U.S.
Patent No. 3,436,366 dated April 1, 1969, assigned to the same assignee as the present invention. The composition of Modic utilizes a vinyl containing diorganopolysiloxane which is incorporated into a silicon hydride-olefin-platinum catalyst composition.
Another SiH-olefin system is shown by Jeram et al, U.S. Patent No. 3,957,713 dated May 18, 1976, which utilizes in addition to the combination of a vinyl containing diorganopolysiloxane, a silicon hydride and a platinum catalyst, a low viscosity organopolysiloxane fluid which is terminated at one end with a trior-ganosiloxy group and the other end a vinyl diorgano-siloxy group. Jeram et al also teaches that a silica filler can be utilized, for example, fume silica or precipitated silica which are preferably treated wlth cyclic polysiloxane or silazane to provide high strength :~ ~ 79~ RD - 1 3 0 1 8 ` compositions in the cured state.
- Additional compositions are shown by Jeram, U.S.
- Patent No. 4,041,010 dated August 19, 1977, directed to fluorosilicone composistions, based on the use of a fluorosilicone, a vinyl fluorosilicone resin, a silicon hydride cross-linking agent and a platinum catalyst which are particularly useful in liquid injection applications. In addition, U.S. Patent 4,029,629 dated June 14, 1977 to Jeram, teaches the use of a reinforcing filler in combination with the aforedescribed silicone composition.
Experience has shown that liquid injection molding apparatus requires that the uncured organopolysiloxane composition have a viscosity of about 10,000 to 25,000 centipoises at 25C so that the organopolysiloxane can be readily injected into the molding chamber and thereafter the composition has to cure at a sufficiently rapid rate. It is also known by those skilled in the art that platinum catalysts, for example, Raskin U.S. patent No. 3,220,472 dated November 30, 1965 and Karstedt, U.S. Patent No. 3,715,334 dated February 6, 1973, are directed to valuable platinum complexes which can be utilized to effect addition between SiH and vinyl containing diorganopolysiloxane. It is further known that use of such platinum catalyst with mixtures of silicon hydride and vinyl containing diorganopolysiloxane do not possess sufficient shelf stability at 25C to be useful as one component curable organopolysiloxane compositions in the form of a mixture of the platinum catalyst, the silicon hydride and the vinyl containing organopolysiloxane. As a result, inhibitors, for example, Bobear, U.S. patent .

~ 7~ RD-13018 No. 4,061,609 dated December 6, 1977 have been developed in the form of hydroperoxy compounds.
However, inhibitors often have been found to interfere with the functioning of the catalyst, particularly in instances where the inhibitor is employed with the platinum catalyst and the vinyl containing diorgano-polysiloxane as part of a two component mixture which can be subjected to elevated temperatures prior to combining the aforementioned ingredients with the silicon hydride component under liquid injection molding conditions.
The present invention is based on the discovery that a halogenated tetrameric platinum complex having the formula lS [Pt(CH3)3(X)]4 (1) where X is a halogen radical, for example, chloro, bromo, iodo, etc., can be utilized in combination with one component silicon hydride containing siloxane and vinyl polydiorganosiloxane liquid mixtures without the use of an inhibitor to produce heat curable organopolysiloxane formulations which can be used in a variety of applications to make high strength cured organopolysiloxanes after an extended shelf period as a liquid mixture. The one component liquid mixtures, for example, can be used with or without reinforcing silica fillers in various applications, such as liquid injection molding. In addition, the platinum catalyst of formula (l) can be utilized in combination with vinyl containing polydiorganosiloxane at elevated temperatures in absence of an inhibitor and thereafter combined with a silicon hydride as part of a two component liquid injection molding formulation. Unlike the platinum ~ ~ 713~ RD-1301~

catalysts of the prior art, which often react with an inhibitor, rendering the platinum catalyst less effective as part of a two component liquid injection moldlng organopolysiloxane formulation, the tetrameric platinum catalysts of formula ~1) are not subject to prior "poisoning" because these halogenated tetrameric complexes of platinum do not require an inhibitor. In addition, inhibitors often have been found to adversely affect the physical properties of the cured organopolysiloxane.
Statement of the Invention A heat curable organopolysiloxane composition comprising (A) a silicone composition comprising (i) 100 parts of a vinyl containing diorganopolysiloxane and (ii) 10 to 20 parts of silicon hydride containing siloxane comprising a member selected from the class consisting of silicon hydride resin consisting essentially of chemically combined diorgano hydride siloxy units and SiO2 units, linear hydride polysiloxane consisting essentially of chemically combined hydro organo-siloxy units and diorganosiloxy units, a linear hydride polysiloxane coupler consisting essentially of chemically combined diorganosiloxy units and terminal diorgano hydride siloxy units, and mixtures thereof (B) an effective amount of the platinum catalyst of formula (1).

RD-1301~

- Certain of the platinum catalysts of formula (1), for example, the corresponding iodo compound, were first prepared by Pope and Peachey in 1909 from methyl maynesium iodide and platinum tetrachloride. See W.J~ Pope and S.J. Peachey, J. Chem. Soc. (1909) 571. The corresponding chloro and bromo analogs can be prepared from the appropriate Grignard reagents. An effective amount of the platinum catalyst of formula (1) has been found to be that amount of catalyst which is sufficient to provide at least 2 ppm to 100 ppm of platinum and preferably from 20 ppm to 30 ppm based on the weight of heat curable organopolysiloxane com-position.
The vinyl containing diorganopolysiloxane or "vinylsiloxane" utilized as one of the principal ingredients in the heat curable organopolysiloxane compositions of the present invention can have a viscosity of from about 100 to 200,000 centipoise.
The vinyl siloxane is included within the following formula:

R R R
C2H3 --sio _ sio r -- si -- C2E[3 R R t R

where C2H3 is vinyl and R is selected from monovalent hydrocarbon radicals free of olefinic unsaturation and t is a positive integer having a value sufficient to provide a vinyl siloxane viscosity of from about 100 to 200,000 centipoise at 25C. Preferably, R is selected from alkyl radicals of 1 to 8 carbon atoms, such as methyl, ethyl, propyl; mononuclear aryl radicals such as phenyl, methylphenyl, ethylphenyl; cycloalkyl radicals, cyclohep-~ .
. - 5 ~ ~7~ 33 tyl and haloalkyl radicals such as 3,3,3-trifluoropropyl.
Preferably, the vinyl siloxane has terminal units of the formula, C2H3(CH3)2sioo.5 which can vary from about 0.05 to about 3.5 and prefer-ably from 0.14 to about 2 mole percent.
The vinylsiloxane of Formula (2) is generally prepared by equilibrating the appropriate cyclo tetrasi-loxane with appropriate vinyl terminated low molecular weight polysiloxane chain-stoppers. The chain-stopper is preferred for such equilibration reaction and is preferably a low molecular weiaht vinyl terminated polysiloxane compounds such as a disiloxane, trisiloxane, tetrasiloxane and so forth. These low molecular weight vinyl terminated polysiloxane polymers are produced by hydrolyzing the appropriate chlorosilanes particularly vinyl diorganochlorosilanes along with diorganodichloro-silanes to produce the desired chain-stopper. This chain-stopper is then taken in a relatively pure form and equilibrated along the cyclotetrasiloxanes with the appropriate substitute groups in the presence of a catalyst to produce the desired vinyl siloxane having a viscosity varying from lO0 to 200,000 centi-poises at 25C. The catalyst that is utilized is preferably a mild acid catalyst~ su~h as toluene, sulfonic acid or an acid treated clay such as filtrol, which a sulfuric acid activated clay manufactured and sold by Filtrol Corporation of Los Angeles, California.
When the equilibration has proceeded to the point where about 85% of the cyclopolysiloxanes have been converted to the linear polymer, the acid catalyst is neutralized with a base or simply filtered out in the RD~1301~
3~ 3 case of the acid activated clay to leave behind the linear polymer. Preferably, excess cyclices are stripped off so that the linear polymer will have a low volatile content and be relatively pure. There can also be utilized an alkali metal hydroxide ~s the catalyst such as for instance potassium or sodium hydroxide.
Included within the silicon hydride containing siloxane, or "silicon hydride" is a hydride "coupler", having the fomula Rl ,Rl Rl H -SiO - - SiO - - Si - H (3) Rl Rl l I Rl where Rl is monovalent hydrocarbon radicals free of olefinic unsaturation and n is an integer having a value sufficient to provide the "coupler" with a viscosity of 1 to 500 centipoises at 25C and from about 3 to 9 mole percent of diorganohydride siloxy units, based on the total moles of chemically combined siloxy units in the linear hydride polysiloxane.
In addition to the silicon hydride coupler of formula (3~, the silicon hydride used in the heat curable polysiloxane compositions of the present invention also can include cross-linking agents such as hydride resins consisting essentially of the following chemically combined units:

H --- SiO
0.5 ~.~L 7'`3~3~'33 RD--13081 units and SiO2 units, where the R2 + H to Si ratio varies from 1.0 to 2.7 and a hydride resin having chemically combined units of the formula, H SiO
, 0.5 with SiO2 and (R )2SiO units were the R + H to Si ratio varies from 1.2 to 2.7, where R , R3 and R4 are monovalent hydrocarbon radicals free of olefinic unsaturation.
These silicon hydrides can be simply produced in the controlled hydrolysis of the corresponding hydride chlorosilanes in the presence of hydrocarbon organic solvent. For the resin containing only monofunctional units and tetrafunctional units, a hydrogen diorg-anochlorosilane is hydrolyzed along with a tetrachlor-osiline to produce the desired resin. In the case of the resin containing the monofunctional siloxy units, the difunctional siloxy units, and the tetra-functional siloxy units, there is hydrolvzed a hydrogen diorgano dichlorosilane, a tetrachlorosilane and a diorganodichlorosilane in the desired ratios to produce the desired resins. Most information as to the process by which said resins are produced, one is referred to the patent of E.M. Jeram, U.S. patent No. 4,040,101 dated August 9! 1977.
In place of hydride resins, the silicon hydride also includes linear hydrogen containing polysiloxane having the formula, ~ 3 ~D-13018 R _ SiO_ SiO ~ SiO ~ SiR (4) 1 5 ~ 5 R R ¦ R ~ R

where R5 is a monovalent hydrocarbon radical free of olefinic unsaturation, and p and q are integers which have values which can vary to provide a polymer viscosity of from l to l,000 centipoises at 25C and wherein the polysiloxane has from 0.04 to 1.4 by weight of hydrogen.
The silicon hydride of formula (4) can be produced by equilibrating the appropriate hydrogen cyclopol-ysiloxane with the appropriate cyclo polysiloxane con-taining R5 substituen groups, in the presence of disiloxane, trisiloxane, and other low molecular weight linear triorganosiloxy end-stopped chain-stoppers.
The process is much the same as producing the vinyl containing polymer; however, "such hydride cross-linking agents" may be made by an alternate process. This alternate process comprises hydrolyzing the appropriate chloxosilanes in water along or in the presence of a hydrocarbon solvent to produce a mixture of cyclics and linear hydride polymers of formula (4) and there-after stripping the mixture of cyclics.
In formulas (3) and (4) and the chemically com-bined units described abo~e, Rl, R2, R3, R4 and R5 can be the same of different radicals selected from the group consisting of alkyl radicals of 1 to 8 carbon atoms such as methyl, ethyl, propyl, etc.; cycloalkyl radicals such as cyclohexyl, cycloheptyl, etc.; mononuclear aryl ` ~79~ RD-13018 radicals such as phenyl, methyl, ethyl, phenyl, etc.;
and haloalkyl radicals such as 3,3,3-trifluoropropyl.
The hydride coupler is prepared by either a hydrolysis process or by acid catalyzed equilibration process.
In the equilibration process the appropriate cyclotet-rasiloxanes are equilibrated a low molecular weight a hydrogen terminated chain-stoppers, such as a dihy drogen tetraorgano disiloxane. The acid catalyzed equilibration reaction is much the same as the disclosed for the production of the vinyl containing base polymer. By the hydrolysis process, the appropriate hydrogen diorganochlorosilanes are hydrolyzed with the appropriate amount of diorganodichlorosilanes to produce the desired polymer of formula (3) above. When the hydride coupler is produced, it can be separated from the undesirable amount of cyclics by stripping.
The hydride coupler and hydride cross-linker is preferably mixed with the vinyl siloxane to form a single package, while some vinyl siloxane is preferably mixed with the platinum catalyst to form another package.
When it is desired to cure the composition, the two packages are simply mixed together and allowed to cure either ~radually at room temperature or rapidly at elevated temperatures, that is, temperatures above 100C.
To obtain the high physical strength of the composition, there may be incorporated from 5 to lO0 parts by weight of a filler based on a lO0 parts of the base vinyl siloxane. A filler can be selected from fumed silica, precipitated silica and mixtures thereof. Preferably less than 50 parts by weight of filler per lO0 parts by weight of the vinyl siloxane ~Lll7'`3~9~

is utilized. In place of the reinforcing filler such as fumed silica and precipitated silicas, there may be utilized extending fillers which do not unduly increase the viscosity of the composition in the uncured state, but increasing to some extent the tensile strength of the composition. The reinforcing and extending fillers are, for instance, titanium dioxide, lithopone, zinc oxide, zirconium silicate, silica aerogel, iron oxide, diatomaceous earth, calcium carbonate, silazane treated silicas, glass fibers, magnesium oxide, chromic oxide, zirconium oxide, aluminium oxide, alpha quartz, calcined clay, carbon, graphite, cork, cotton, synthetic fibers and so forth.
For liquid injection molding applications, it has been found desirable to limit the viscosity below 500,000 centipoises at 25C and more preferably, below 200,000 centipoises at 25C.
One method of increasing the tensile strength of the composition without unduly increasing the uncured viscosity is to incorporate a vinyl containing resin in the composition. Accordingly, per 100 parts by weight of the vinyl siloxane, there may be present from 10 to 100 parts by weight of an organo polysiloxane copolymer having chemically combined (R6)3SiOo 5 units and SiO2, where R6 is a radical selected from the class containing of vinyl radicals, alkyl radicals and aryl radicals, and fluoroalkyl radicals of 1 to 8 carbon atoms with a ratio of monofunctional units and tet-rafunctional units, is from 5:1 to 1:1 and where from about 2.5 to 10 mole percent of the silicon atoms contains silicon bonded vinyl groups.

A somewhat different procedure which also can be R~-13018 ~ 7~
used to increase the -tensile strength of the cured composition without unduly increasing the viscosity of the uncured total composition is by incorporating, per 100 parts of the vinyl siloxane, from 10 to 100 parts by weight of an organo polysiloxane copolymer having chemically combined (R7)3Sioo 5 units, (R7)2Sio units and SiO2 units, where R7 is a radical selected from the class consisting of vinyl radicals, aryl radicals, alkyl radicals, alkyl radicals and fluoroalkyl radicals with a ratio of monofunctional units, difunctional units is from 0.5:1 to l:l and the difunctional units are present in an amount equal from about 1 to 10 mole percent based on the total number of siloxane units in the copolymer and where from about 2.5 to 10 mole percent of the silicon atoms contains silicon bonded vinyl groups. For information as to the utilization of such resins in addition curing compositions one is referred to the issued patent of F.J. Modic, U.S.Patent 3,436,366 dated April ll 1969.
In the above units of the resin, R7 has been disclosed as being selected from vinyl radicals, aryl radicals, and alkyl radicals and fluoroalkyl radicals, more preferably, R7 is selected from vinyl radicals, alkyl radicals of l to 8 carbon atoms, phenyl radicals and 3,3,3-trifluoropropyl radicals.
The vinyl siloxane also can include a polysi-loxane polymer having a vinyl group at one terminal position of the siloxane chain and a triorgano siloxy group on the other terminal position of the polysiloxane chain. Accordingly, per 100 parts of the vinyl siloxane containing polymer, there may be utilized from 5 to 40 parts by weight a diorganopolysiloxane of the formula, ~ 33 RD-13018 R8 ¦ R ~ R8 l , R _ sio ~ io ~ si _ C2~l3 (5) R j R9 ~ wR8 where R8 is a monovalent hydrocarbon radical free of olefinic unsaturation, and R9 is monovalent hydrocarbon radical, and w is an integer having a positive value suffi-cient to provide a viscosity of the diorganopolysiloxane varying from 50 to 50,000 centipoises at 25C.
In foxmula (5), R8 is more particularly an alkyl radical of 1 to 8 carbon atoms, a phenyl radical or a 3,3,3-trifluoropropyl radical, where R9 can be selected from R8 radicals. These polymers and their use in such Si~l-olefin-platinum catalyst compositions are further shown in U. S. Patent No. 3,957,713 dated May 18, 1976, Jeram et al.
In order that those skilled in the art will be better able to practice the present invention, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.
Example 1.
. . .
Approximately 3.3 parts of thoroughly dried and deacidified platinum tetrachloride was added to a rapidly stirring mixture of ~.8 parts of methylma~nesium iodide in 100 parts of tetrahydrofuran. After the addition was completed, the resulting dark red solution was hydro-- lyzed and extracted with toluene until the organic layer remained colo-~less. Stripping the combined extracts provided a 68% yield or 2.4 parts of an orange-yellow solid having a melting point of 188-190C.
The product was then washed with pentane at -78C.
Based on method of preparation, the product was ~17~ RD-13al8 [Pt(CH3)3I]~

A gel time study was performed with various platinum catalysts with a mixture of 10 parts of a vinyl chain-stopped polysiloxane and 1 part of a liquid organo hydrogen polysiloxane as shown in Modic U.S. Patent No. 3,436,366 dated April 1, 1969, assigned to the same assignee as the present invention.
The vinyl chain-stopped polysiloxane was more particularly a mixture of 125 parts of a dimethylvinyl end-stopped polydimethylsiloxane fluid having a viscosity in the range of 3,000-4,000 centipoises and 42 parts of a dimethylvinyl end-stopped polydimethylsiloxane resin having about 2 mole percent chemically combined dimethylvinylsiloxy units. The liquid organo hydrogen polysiloxane was a dimethyl hydrogen end-stopped polydimethylsiloxane fluid having a viscosity of less than about 1,000 centipoises at 25C.
The liquid vinyl chain-stopped polysiloxane was mixed with the liquid organo hydrogen polysiloxane prior to catalyst addition. Gel times were run on a Sunshine Instrument Timer in 13 mm OD test tubes.
The following results were obtained, where "Faltynek"
is the platinum catalyst utilized in the practice of the present invention, Lamoreaux is 4(H2PtC16/N-Octanol) as described in U.S. Patent 3,220,972 dated November 30, 1965 and Karstedt is (PtO/ divinyl-tetramethyldisiloxane) as shown in U.S. Patent No.
3,715,334 dated February 6, 1973.

-- 1~ --PPM Gel Time Catalyst Temp. CPlatinum(min) Faltynek 25 30 > 35,000 Lamoreaux 25 35 384 Karstedt 25 25 40 Faltynek 52 30 1,120 Lamoreaux 52 18 337 Karstedt 50 25 8 Faltynek 100 3 94 Lamoreaux 100 4 25 Karstedt 100 4 14 Faltynek 155 3 7 Lamoreaux 155 3 3 Karstedt 150 4 3 The above results show that the platinum catalyst of the present invention "Faltynek" provides a longer pot life and temperatures in the range of from 25C
to 155C than platinum catalyst of the prior art.
Example 2.
- A heat curable organopolysiloxane composition was prepared by incorporating an effective amount of the halogen containing platinum tetramer of Example 1 into a vinyl siloxane and thereafter mixing the vinyl siloxane "component A", with a silicon hydride siloxane "component B" for 10 to 15 minutes in a planetary mixer. The resulting heat curable organo-polysiloxane compositions contained 20 ppm of platinum.
Component A consisted of 53 parts of a vinyl end-stopped polydimethylsiloxane fluid having a viscosity of 50,000-80,000 centipoises at 25C, 10 parts of a dimethylvinyl end-stopped polydimethylsiloxare resin ~ 7'~ RD-13018 having about 2 mole percent of chemically combined dimethylsiloxy units, 4 parts of a dimethylvinyl end-stopped polydimethylsiloxane fluid having about 0.06 : mole percent of dimethylvinylsiloxy units and a viscosity of 40,000 centipoises, 12 parts of fumed silica treated with hexamethyl disilazane and 8 parts of ground quartz having a final viscosity of about l,OOO,OQ0 centipoises. Component B consisted of 5 parts of dimethyl hydrogen end-stopped polydimethyl-siloxane fluid having a viscosity of 1,000 centipoises at 25C, 53 parts of vinyl end-stopped polydimethyl-siloxane fluid having a viscosity of 50,000-80,000 centipoises, 10 parts of a dimethylvinyl end-stoppea polydimethylsiloxane resin having about 2 mole percent of chemically combined dimethylsiloxy units, 12 parts of silazane treated fumed silica and 7 parts of ground quartz.
The above heat curable organopolysiloxane com-position was injected into a mold cavity and heated for 15 minutes at 35QF and post baked for 4 hours at 400F. The following properties were obtained in the resulting cured slab after the initial 15 minute cure, followed by the 4 hour post bake period, where "H"
is hardness (shore A~, "T" is tensile (psi~, "E" is elongation (%~ and "T" is tear (pi).

T' 120/160 The above procedure was repeated, except that the platinum concentration was reduced to 4 ppm.

~ D-13018 T' 130/lS0 The above results show that the platinum catalyst of the present invention can be used to make valuable compression molded parts when utilized in combination with curable organopolysiloxane composition.
Example 3.
In accordance with the procedure of Example 2, another liquid injection molding mixture was prepared consisting of a mixture of a vinyl siloxane and a silicon hydride siloxane and 20 ppm of the platinum tetramer of Example l.
Component A and component B of the liquid injection moldable composition was substantially the same as component A and component B of the liquid injection molding composition of Example 2, except that in place of the lO parts of the dimethylvinyl end-stopped polydimehylsiloxane resin having about 2 mole percent of chemically combined dimethylsiloxy units, there was utilized respectively, 38 parts of the same dimethylvinyl end-stopped polydimethylsiloxane resin in the liquid injection molding composition.
The above heat curable organopolysiloxane com-position was injected into a mold cavity and heated for 15 seconds at 400F and then post baked at 400F
for 4 hours. The following proporties were obtained where H, T, E and T' are as defined in Example 2:

3~ RD--13018 T' 130/110 The above results show that a high strength, shaped, substantially cured organopolysiloxane com-position was obtained after 15 seconds at 400F which shows that the heat curable organopolysiloxane composition containing the platinum tetramer of the present invention is a valuable injection moldable composition.
Example 4.
A pot life study was made to determine the sta-bility of mixtures of 20 ppm of various platinum catalysts in a vinyl siloxane corresponding to component A of Example 2. It has been found that if the platinum catalyst reacts with silicon vinyl siloxy units, a liquid injection moldable mixture can gel within 4 to 8 hours on mixing the vinyl siloxane "component A" with the silicon hydride siloxane "component B".
In order to determined the stability of the Faltynek catalyst as compared to the Lamoreaux catalyst of Example 1, vinyl siloxane mixtures were prepared containing 20 ppm of the respective catalysts and held for 5 days at 70Co The vinyl siloxane utilized was the same as shown in Example 2, referred to as component A, except that there was utilized 38 parts of the dimethylvinyl end-stopped polydimethylsiloxane resin instead of 10 parts as shown in Example 2. The respective platinum containing vinyl siloxanes were were then cooled to 250C and mixed with the silicon hydride siloxane "component B" of Example 2. The :~ 7'3~3 RD-l3ol8 - resulting liquid injection moldable mixtures were tested for viscosity increases. The following results were obtained:
Pt Catalyst Gel Time . . _ . .
Lamoreaux ~ hr.
Faltynek > 3 weeks The above results show -that the Faltynek catalyst of the present invention does not react with vinyl radicals attached to silicon after extended periods at temperatures as high as 70C~ As a result, an inhibitor is not required and liquid injection molding compositions as one package or two package systems without the need for refrigeration are provided. In addition, a solution of .05 mole of the platinum tetramer of Example 1 in trimethyl silane was found to remain unchanged for at least 16 hours at 150C based on NMR spectra.
Although the above examples are directed to only a few of the very many variables which can be employed in the practice of the method of the present invention to make the heat curable organopolysiloxane compositions, it should be understood that the present invention is directed to the use of a much broader variety of vinylsiloxane and silicon hydride siloxane as well as halogen containing platinum tetramer which are shown in the description preceding these examples.

Claims (9)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A heat curable organopolysiloxane composition comprising:
(A) a silicone composition comprising (i) 100 parts of a vinyl containing diorgano-polysiloxane, and (ii) 10 to 20 parts of a silicon hydride containing siloxane, and (B) an effective amount of platinum catalyst having the formula [Pt(CH3)3(X)]4, whereby the need for an inhibitor is avoided, where X is a halogen radical selected from iodo, chloro and bromo.

2. A heat curable organopolysiloxane composition comprising:
(A) a silicone composition comprising (i) 100 parts of a vinyl containing diorganopolysiloxane, and (ii) 10 to 20 parts of silicon hydride containing siloxane comprising a member selected from the class consisting of silicon hydride resin consisting essentially of chemically combined diorganohydride siloxy units and SiO2 units, linear hydride poly-siloxane consisting essentially of chemically combined hydro organosiloxy units and diorganosiloxy, a linear hydride polysiloxane coupler consisting essentially of chemically combined diorganosiloxy units and terminal diorgano hydride siloxy units, and mixtures thereof, and (B) an effective amount of platinum catalyst having the formula [Pt(CH3)3(X)]4, where X is a halogen radical selected from iodo, chloro and bromo.

3. The heat curable composition of claim 1, where the platinum catalyst has the formula [Pt(CH3)3I]4.

4. The heat curable composition of claim 1, where the vinyl containing diorganopolysiloxane is a vinyl terminated polydimethylsiloxane having a viscosity in the range of from 3,000 to 80,000 centipoise at 25°C.

5. The heat curable composition of claim 2, where the vinyl containing diorganopolysiloxane is a mixture of a vinyl end-stopped polydimethylsiloxane having a viscosity of from 50,000 to 80,000 centipoise, a dimethylvinyl-terminated polydimethylsiloxane resin having about 2 mole percent of chemically combined vinyl dimethylsiloxy units, and a dimethylvinyl-terminated polydimethylsiloxane fluid having a viscosity of about 40,000 centipoise; the silicon hydride containing siloxane is a dimethyl hydrogen-terminated polydimethylsiloxane fluid having a viscosity of about 1,000 centipoise; and the heat curable composition is reinforced with a mixture of fumed silica and ground quartz.

6. The heat curable composition of claim 1, containing a silica filler.

7. The heat curable composition of claim 4, where the platinum catalyst has the formula [Pt(CH3)3I]4 and is sufficient to provide from 2 to 100 ppm of platinum.

8. In the method for effecting addition between a vinylsiloxane and a silicon hydride siloxane in the presence of a platinum catalyst, whereby an inhibitor is required to lengthen the shelf life of the resulting mixture at ambient temperatures, the improvement which comprises utilizing as the platinum catalyst an effective amount of a halogen containing platinum tetramer having the formula [Pt(CH3)3(X)]4 whereby the need for an inhibitor is avoided, where X is a halogen radical selected from iodo, chloro and bromo.

9. The method of claim 8, where the platinum catalyst is [Pt(CH3)3I]4.