patent for silicone in implants.....ingredients part 1

[Guest guest]

http://www.patentstorm.us/patents/5534609/description.html

US Patent 5534609 - Polysiloxane compositions

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to adherent polysiloxane compositions, products and

articles of manufacture produced therefrom, and methods of use thereof. In

particular, the invention relates to polysiloxane compositions that have

the SiH3 functionality therein and can be cured to yield elastomeric

gels capable of adhering to a variety of surfaces.

2. Description of Related Art

Silicone rubbers, gels, and elastomers are elastic materials typically

prepared by crosslinking linear polyorganosiloxanes. Heinz-Herman,

"Rubber, 1. Survey," Ullman's Encyclopedia of Industrial Chemistry, Vol.

A23 (1993), VCH Publishers, Inc.; Osada, et al , "Intelligent Gels,"

Scientific American, (May, 1993) pages 82-87; Almdal, et al., Polymer Gels

and Networks, (1993), Vol. 1, pages 5-17. These materials are valued for

their resistance to environmental, chemical and biochemical degradation,

and for the retention of their tensile and other physical properties even

after exposure to extremely high or low temperatures for long periods.

Uses for silicone elastomers include encapsulants for electronic

components, breast prostheses, waterproof and rust-proof coatings on

metals, non-stick coatings on medical devices, dental impression gels and

shock absorbing cushions in footwear and automobiles. Usually, it is

essential that the polysiloxane composition have adequate cohesive

strength as well as excellent adhesive strength when in contact with

various substrates.

Gels, elastomers and rubbers are differentiated by the extent of

crosslinking within the siloxane network and by hardness and elasticity.

That is, hardness and elasticity are a function of crosslinking, as well

as the specific raw materials used (e.g., shorter molecules lead to less

elasticity). One quantitative measure of this difference is the modulus or

resistance to deformation. Modulus is measured in units of force per unit

area; for example, modulus units can be newtons per square meter,

N/m2, also called a Pascal, Pa. Rubbers typically have moduli of

about 105 -106 Pa, whereas gels have moduli of about 102

-105 Pa. The crosslinked polysiloxane compositions of this invention

are silicone gels and rubbery elastomers.

Crosslinking, also referred to as curing or vulcanization, can be effected

with organic peroxides, high energy radiation or organometallic catalysts.

Heat is often applied to initiate the peroxide and metal-catalyzed

crosslinking reactions. The method selected depends on factors such as the< google_ad_client = "pub-4613161156835561"; google_ad_width = 336; google_ad_height = 280; //New PS - Description 2nd ad - 1/4/08 google_ad_slot = "1886262892";

r /> composition of the polyorganosiloxane, the time and temperature required

for curing and the cost of manufacturing. Crosslinking with organometallic

catalysts occurs either by addition cure or condensation cure.

Typically, addition cure is catalyzed by a divalent or zerovalent platinum

compound as described in U.S. Pat. Nos. 3,419,593 and 3,775,452. Addition

cure is characterized by the hydrosilation reaction of an unsaturated

linkage such as, for example, vinyl, alkynyl or allyl by a hydrosiloxane

group, Si--H, to yield Si--C bonds. Condensation cure is usually catalyzed

by tin or titanium catalysts, examples of which are disclosed in U.S. Pat.

Nos. 3,186,963 and 3,708,467. In condensation cure, silanol groups combine

to produce Si--O--Si linkages and water. The equations below illustrate

both processes.

Addition Cure by Hydrosilation

Si--CH.dbd.CH2 +H--Si.fwdarw.Si--CH2 --CH2 --Si

Condensation Cure

Si--OH+HO--Si.fwdarw.Si--O--Si+H2 O

One deficiency of cured polyorganosiloxane gels and elastomers is their

relatively poor adhesion to various substrates such as glass, metals and

organic polymers. Several attempts have been described to correct this

deficiency. For example, U.S. Pat. No. 4,401,500 teaches the use of a

mixture of an alkyltrialkoxysilane and an organic hydroperoxide in an

organic solvent as a primer composition to improve the adhesion of

elastomeric siloxanes to organic and inorganic substrates. Japanese Patent

Nos. 84/220,347, 84/220,348 and 84/220,349 describe a primer composition

that contains a high viscosity methylvinylpolysiloxane fluid, a

methylphenyl-siloxane resin, ?-methacryloxytrimethoxysilane, ethyl

silicate, a methylhydridopolysiloxane, a platinum catalyst and a titanium

catalyst in a toluene/ethyl acetate solvent.

U.S. Pat. Nos. 3,669,072, 4,082,726, 4,196,173, 4,311,739, and 4,087,585

teach that the primer step can be eliminated by direct inclusion of

adhesion promoters such as vinylalkoxysilanes, vinyl epoxysilanes and

epoxyalkoxysilanes in the elastomer formulation. U.S. Pat. No. 4,558,082

teaches that addition of N-vinylpyrrolidinone to a photocurable acrylated

siloxane polymer improves the adhesion of the polymer to paper and

polyethylene. Polysilsesquisiloxanes that have hydrido and alkoxy

functionalities are described as adhesion promoters for curable

polyorganosiloxanes in U.S. Pat. No. 4,677,161. Japanese Patent 74-31,286

teaches that silicone rubber compositions that contain alkoxysilanes,

HSi(OR)3, such as triethoxysilane have excellent adhesion to metals

and plastics.

Silanes that have hydrolyzable R--Si(OR)3 structures with a single SiH

bond are well-known as adhesion promoters, as described in E. P.

Plueddemann's Silane Coupling Agents (1982).

Polyorganosiloxane gels and elastomers can exhibit poor curing behavior

when in contact with some surfaces, especially organic polymer films. This

inhibition is probably caused by additives that make the polymer films

stable to heat, light and biodegradation. The additives and/or the thermal

decomposition products of these additives diffuse into the formulation and

inhibit the crosslinking reactions. Simultaneously, adhesion of the

elastomer to the polymer film can also be impaired.

In the formulation of curable polysiloxane gels and elastomers, additives

are often included that temporarily inhibit the hydrosilation reaction

(also known as hydrosilylation) to permit operations such as thorough

mixing, manipulation, and mold or cavity filling while the composition is

still readily flowable at room temperature. The time needed for these

operations is called the work time or pot life. Upon completion of these

operations, the vulcanization is then initiated by heat, light or

radiation.

The reference, by B. Marciniec, Comprehensive Handbook on Hydrosilation,

Pergamon Press, NY 1992, pg. 190, lists various temporary catalyst

inhibitors. Octylsilanes having the primary silane group, SiH3, are

not included in that list, and are otherwise not known in the art to be

temporary catalyst inhibitors.

U.S. Pat. No. 3,553,164 describes resin compositions that are derived from

primary silanes and dialkenyldisiloxanes via H2 PtCl6 -catalyzed

hydrosilylation. The resulting resins are highly crosslinked, brittle, and

lack the elasticity of elastomers and gels. a, ?-Dialkenyl

oligomeric and polysiloxanes are not described or used in that patent to

obtain more elastic reaction products. In fact, Zhdanov et al., Polymer

Science, USSR, A16(1974) 2,044-2,048, English Translation, have shown that

hexachloroplatinic acid (H2 PtCl6) does not catalyze the SiH to

vinyl crosslinking in high molecular weight substrates, for example

between a,?-dihydrido-polydimethylsiloxanes and vinylsiloxanes

at 70°-140° C.

Various references such as (1) R. A. Benkeser et al. J. Organometallic

Chemistry, 184(1980) C3-C9, or (2) V. O. Reikhsfel'd et al., Russian J.

General Chem. 36(1966), 1,478-1,480, or (3) ibid., 37(1967) 2,436-2,440,

English Translation, teach that compounds that have the SiH3 group do

not undergo smooth and complete reaction of all three Si--H bonds during

platinum-catalyzed hydrosilation. Moreover, these compounds often inhibit

the complete stoichiometric hydrosilylation of compounds that have only

SiH2 or Si--H groups.

We have found that the use of SiH3 -containing compounds in

polysiloxane compositions offers adhesion and working time benefits that

were not heretofore obtainable.

SUMMARY OF THE INVENTION

Accordingly, objects of the present invention include the development of

siloxane compositions that have advantages such as extended work times and

excellent adhesion to various surfaces including polyurethane surfaces.

These advantages are provided ideally without delay of cure at the

vulcanization temperature, or loss of other advantageous features of the

cured polysiloxane such as, for example, feel, elasticity, cohesive

strength, and durable resilience.

These and other objectives of the instant invention have been realized by

use of both an adhesion promoting crosslinker that contains the SiH3

functionality and a conventional network crosslinker.

The siloxane composition comprises:

(A) a polydiorganosiloxane that contains at least two unsaturated

hydrocarbon groups per molecule,

( a polyorganohydrosiloxane that has at least three Si-H bonds per

molecule,

© a compound that has at least one --SiH3 group,

wherein the amount of (A) is between about 10 wt. % and 95 wt. %

(preferably between about 10 wt. % and 80 wt. %, most preferably between

about 15 wt. % and 35 wt. % );

and wherein the amount of ( is between about 0.1 wt. % and about 50 wt. %

(preferably between about 0.4 wt. % and about 10 wt. %);

and wherein the amount of © is between about 0.01 wt. % and about 5.0 wt.

% (preferably between about 0.01 wt. % and about 1.0 wt. %, and most

preferably between about 0.05 wt. % and about 0.5 wt. %);

and wherein the amounts of (A)-© are relative to each other; and

(D) an effective amount of hydrosilation catalyst.

Component (A) may be represented by the formula

R'--SiR2 --O(SiR2 --O)n --SiR2 --R'

wherein R is a C1 -C20 saturated group (preferably C1

-C12), R' is a C1 -C20 unsaturated group (preferably

C1 -C12) that can undergo a hydrosilation reaction, n is greater

than about 100 (preferably between about 200 and about 2,000).

Component ( may be represented by the formula

##STR1##

or a cyclic structure, (RSiHO)y, such as

##STR2##

wherein R is a C1 -C20 saturated group (preferably C1

-C12), x is greater than 1 (preferably between about 1 and about

100), y is at least three, the sum of e and g is at least three, a, c, d,

e, f, and g are any positive numbers (preferably, a is between about 0 and

about 100).

Component © may be represented by the formula

R4 (SiH3)k,

or

H3 Si(CH2)u SiH3,

or

Ar (SiH3)m,

wherein R4 is a C3 -C20 hydrocarbon group, Ar is an aryl

ring, k and m are at least one, u is between about one and about 20.

Component © may also be any siloxane compound containing the SiH3

grouping. These compounds may be represented by formulae such as H3

SiOSiH3, H3 SiOSiR35, H3 SiO(SiR25

O)a SiH3 and H3 SiO(SiR25 O)a

SiR35, wherein R5 is a C1 -C20 hydrocarbon group

that can be linear, cyclic or branched and can be saturated or

unsaturated. The subscript, a, may be any positive number (preferably,

between 0 and about 100).

The SiH3 -bearing silane or siloxane may additionally contain

heteroatoms such as boron, aluminium, tin, nitrogen, phosphorus, antimony,

sulfur and selenium, provided that these heteroatom-containing silanes and

siloxanes do not completely inhibit the crosslinking reaction, or in any

other way diminish the benefits of the instant invention. C4 H9

N(SiH3)2 and (CH3)3 BN(SiH3)2 are suitable

examples.

Component (D) may be a platinum group metal or a compound of such a metal.

Persons skilled in the art would be aware of the amount of component (D)

necessary to effectively catalyze hydrosilation.

Optionally, the composition may further comprise compound (E), which is a

polydiorganosiloxane compound that is represented by the formula

##STR3##

wherein R is a C1 -C20 saturated group (preferably C1

-C12), p is between about 50 and about 1,500 (preferably between

about 100 and about 500) and a, d and x are the same as defined above with

respect to B and C3,

and the amount of (E) is between about 30 wt. % and about 90 wt. %

(preferably between about 70 wt. % and about 85 wt. %);

and wherein the amounts of (A), (, © and (E) are relative to each

other.

The composition may further comprise temporary catalyst inhibitors, such as

acetylenic alcohols, cyclic methylvinylsiloxanes, alkynyl silanes,

conjugated enynes, and maleate esters.

In addition, the composition may further comprise reinforcing inorganic

fillers, non-reinforcing inorganic fillers and/or thixotropic additives,

and pigments and/or dyes.

In a further embodiment, the invention relates to an external breast

prosthesis that comprises the above-described polyorganosiloxane

composition and a prosthesis bag, wherein the composition adheres to

prosthesis bag.

The above-listed ingredients of the composition can be allowed to react to

form a cured gel or elastomer that has many advantages including:

(1) excellent adhesion of the cured siloxane to polyurethane-polyester

substrates without the use of surface primers,

(2) excellent adhesion of the cured siloxane to polyurethane-polyester

envelopes that are used in the manufacture of external breast prostheses

without loss or degradation of desirable features such as feel,

elasticity, modulus and cohesive strength, and

(3) excellent resilience of the external breast prosthesis, especially when

subjected to digital deformation.

Thus, in yet another embodiment, the invention relates to methods to

promote adhesion of the above-described composition to a substrate,

comprising curing the composition in contact with the substrate.

The invention also relates to methods of temporarily inhibiting catalyst

activity in a hydrosilylation reaction, comprising curing the

above-described composition.

In the methods of the invention, components (A), (, and © of the

composition may be mixed and component (D) is added thereafter. Similarly,

components (A), (, and (D) of the composition may be mixed and component

© is added thereafter. Alternatively, components (A), (, © and (D)

of the composition may be combined in a two-part formulation before

curing, wherein a first part of the two-part formulation comprises

component © and a second part of the two-part formulation comprises

component (D).

The present invention describes among other things the hereinabove-cited

composition, the product formed by curing this composition, articles

produced from this composition, and methods of use for this composition.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The component (A) can be a polydiorganosiloxane that has at least two

unsaturated hydrocarbon groups per molecule. In particular, component (A)

may be represented by the formula

R'--SiR2 --O(SiR2 --O)n --SiR2 --R'

wherein R is a C1 -C20 saturated group (preferably C1

-C12), R' is a C1 -C20 unsaturated group (preferably

C1 -C12) that can undergo a hydrosilation reaction, n is greater

than about 100 (preferably between about 200 and about 2,000). For

example, R' can be methyl, ethyl, phenyl, tolyl, trifluoropropyl or

heptafluoropropyl, and R' can be vinyl, allyl, vinylcyclohexyl, styryl or

propargyl.

Preferably, the polydiorganosiloxane can be a linear polydimethylsiloxane

that has a vinyl group attached to the silicon atom at each chain

terminus. Additionally, the polydiorganosiloxane can be a copolymer, a

block copolymer or mixed-substituent polymer wherein the organo groups, R,

as defined hereinabove, are not all the same.

Examples of component (A) include the following:

R'--SiMe2 --O--(SiMe2 --O)h --(SiArMe--O)j --SiMe2

R'

R'--SiMeArO--(SiMe2 --O)h --(SiMeRf --O)j --SiMeAr--R'

in which R' has the same meaning as defined hereinabove, Me is methyl, Ar

is an aryl group such as phenyl, and Rf is a fluoroalkyl group such

as, for example, trifluoropropyl. The subscripts h and j can be positive

numbers.

Component (A) can be olefinically terminated polydiorganosiloxanes that

have a unimodal molecular weight distribution. These materials are

well-known in the art and are available commercially. Representative

syntheses are reported in, for example, Polymer Preprints, No. 10 (1969),

1,361 and Acta Polymerica. 42(1991) 107-109, the complete disclosures of

which are incorporated herein by reference.

Alternatively, component (A) can be a blend of products such that the blend

has a bimodal or higher modal molecular weight distribution. The viscosity

of component (A), either as a single product or as a blend, can be between

about 150 and about 500,000 centistokes and, preferably, between about 500

and about 100,000 centistokes. It is desirable that component (A) be

substantially free from silanol groups, SiOH. The silanol content should

be less than 150 ppm and, preferably, less than 50 ppm. Component ( can

be a linear or branched polyorganohydridosiloxane that contains at least

three Si--H bonds per molecule. In particular, component ( may be

represented by the formula

##STR4##

or a cyclic structure, (RSiHO)y, such as

##STR5##

wherein R is a C1 -C20 saturated group (preferably C1

-C12), x is greater than 1 (preferably between about 1 and about

100), y is at least three, the sum of e and g is at least three, a, c, d,

e, f, and g are any positive numbers (preferably, a is between about 0 and

about 100).

The Si--H bonds can be distributed in various ways along the polymer chain,

including random distribution among internal and terminal positions. The

person having ordinary skill in the art can readily determine the optimum

network crosslinking, adhesion and desirable feel of the silicone gel.

Other examples of component ( products include:

##STR6##

in which R, Rf, Me and Ar have the same meanings as defined

hereinabove. Subscripts x and r can be between about 1 and about 100 and

are, preferably, between about 15 and about 75. Subscript c is a positive

number. In branched polyorganohydridosiloxanes, the sum of x and r is

preferably between about 15 and about 75. The subscripts, q, y and z can

be any positive numbers provided that the total of Si--H bonds per

molecule is at least three.

Although use of a single polyorganohydridosiloxane of unimodal molecular

weight distribution and well-defined functionality for crosslinking is

customary, blends of polyorganohydridosiloxanes of high and low

functionalities and molecular weights can sometimes offer gels with

balanced cohesive gel strength, softness and adhesion, as readily

determined by the person having ordinary skill in the art.

The functionality of component ( is the number of Si--H bonds per

molecule. Star-branched crosslinkers are also preferred network

crosslinkers, such as, for example:

Si[OSi(CH3)2 H]4

or

Si[O(Si(CH3)2 O)4 Si(CH3)2 H]4.

Products satisfying the requirements for component ( are well-known in

the art and are available commercially. Syntheses of these products have

been published in, for example, W. Noll, Chemistry and Technology of

Silicones, Academic Press, NY 1968, the complete disclosure of which is

incorporated herein by reference.

Component © is a compound that bears the SiH3 functional group, such

as primary silanes and siloxanes with a terminal --SiH3 group.

Examples include the primary silanes having the general formulae, R4

(SiH3)k, H3 Si(CH2)u SiH3, and

Ar(SiH3)m, wherein R4 can be a C3 -C20

hydrocarbon group that can be linear, cyclic or branched and can be

saturated or unsaturated. Ar can be a substituted or unsubstituted aryl

radical such as phenyl, tolyl, ethylphenyl or xylyl. Primary alkylsilanes

that have fewer than three carbon atoms normally have boiling points

<0° C. and might be too volatile to be effective under the

conventional platinum-catalyzed thermal vulcanization conditions. The

value of k can be at least one and, optionally, can equal an integer up to

twice the number of carbon atoms in R4. The value of m can be at

least one and, optionally, is equal to the number of carbon atoms in the

aryl radical. The value of u can be between about 1 and about 20.

Suitable primary silanes useful as adhesion promoting crosslinkers include

amylsilane (C5 H11 SiH3), hexylsilane (C6 H13

SiH3), octylsilane (C8 H17 SiH3) (preferred),

cyclohexylsilane (C6 H1l SiH3), phenylsilane (C6

H5 SiH3), and octadecylsilane (C18 H37 SiH3).

Additional primary silanes include H3 Si(CH2)u SiH3,

wherein u can be between about one and about 20, and the ortho, meta and

para isomers of C6 H4 (SiH3)2.

Suitable SiH3 -containing siloxanes useful as adhesion promoting

crosslinkers include H3 SiOSi(CH3)3, H3 SiOSi(C5

H11)3, H3 SiOSi(C2 H3) (CH3)2, H3

SiOSi (C2 H3)3, H3 SiO[si(CH3)2 O]4

SiH3 and H3 SiO[si(Ar)2 O]3 Si(C3 H5)

(C8 H17)2.

Component © is useful as an adhesion promoter in that it improves the

adhesion between the cured polysiloxane composition and contacting

surfaces, especially surfaces of polymeric substrates that contain

polyurethane and/or polyester. To that end, one or more of the adhesion

promoting crosslinkers © may be employed or, in the alternative, one or

more of the adhesion promoting crosslinkers © in combination with other

conventional adhesion promoting compounds may be used.

Component © is also quite useful to temporarily inhibit the catalyst

activity in a hydrosilation reaction. One or more of the compounds of

component © may be employed or, in the alternative, one or more of the

compounds of component © in combination with other conventional adhesion

promoting compounds may be used, as described below.

The hydrosilation catalyst, component (D), can be a platinum group metal or

a compound of such a metal. Further, component (D) can be an addition cure

hydrosilation catalyst. Examples include platinum (II) and zerovalent

platinum complexes, as well as colloidal platinum. The organometallic

complexes of platinum with 1,3-divinyltetramethyldisiloxane and low

molecular weight vinyl end-blocked organosiloxanes are preferred. These

complexes are described in, for example, U.S. Pat. Nos. 3,419,593;

3,516,946; 3,775,452; 3,814,730; 4,288,345 and in Angewandte Chemie,

International Ed., 30(1991) 438-440. Complexes with alkynes are described

in, for example, U.S. Pat. No. 4,631,310. The complete disclosures of each

of these references is incorporated herein by reference.

Component (E) is a polydiorganosiloxane compound that functions as a

rheology modifier. This means that component (E) influences the flow

(viscosity), extension (elasticity), tension, dampening and deformation

properties of the cured elastomer or gel. The magnitude of this influence

depends both on the molecular weight of component (E) and on its

concentration in the siloxane composition. Component (E) should be fluid,

miscible with and unreactive with components (A), (, © and (D).

The crosslinking reactions between the SiH bonds of components ( and ©

and the unsaturated linkages of component (A) are accompanied by enormous

changes in the rheology of the siloxane composition. Most notably,

increases occur in viscosity, elasticity and modulus. The magnitude of the

increases is determined by, among other variables, the crosslink density

and the concentration of crosslinked polymer. Higher crosslink densities

are usually associated with high modulus, high viscosity and low

elasticity. Conversely, low crosslink density typically leads to the

opposite of these properties. Elasticity is increased by a higher

molecular weight between crosslinks. When the crosslinking reaction is

conducted in the presence of component (E), the concentration of

crosslinked, viscoelastic polymer in the siloxane composition is

effectively reduced. Control of polymer concentration affords process

control over the rheological properties of the elastomeric or gel product.

For example, increases in polymer concentration bring about increases of

viscosity, dampening and modulus. Increasing the molecular weight or

viscosity of component (E) will also increase the probability of

entanglements between the molecular chains of the crosslinked,

viscoelastic polymer and those of component (E). This increased

entanglement raises the overall viscosity of siloxane composition,

improves its dampening ability and its capacity to return to its original

condition following deformation. Rheological changes occurring during

crosslinking reactions are reviewed by A. Y. Malkin, POLYMER ENGINEERING &

SCIENCE, Vol. 20 (1980) 1035-1044 and C. W. Macosko, BRITISH POLYMER

JOURNAL, Vol. 17 (1985) 239-245, the entire content of which references

are herein incorporated by reference. The mathematical relationships among

molecular properties, concentration and rheology are taught in J. D.

Ferry, Viscoelastic Properties of Polymers, 3rd edition, Wiley &

Sons, NY 1980 and in R. G. Larson, Constitutive Equations for Polymer

Melts and Solutions, Butterworths, Boston, 1988, the entire contents of

which references are herein incorporated by reference.

Component (E) can be a linear or branched polyorganosiloxane that is

essentially free of (1) unsaturated groups that can undergo hydrosilation

and (2) silanol groups. Component (E) can contain cyclic

diorganosiloxanes. For optimum rheological properties in the gel, it is

preferable that component (E) have a viscosity less than that of component

(A).

In particular, component (E) can be represented by the formula

##STR7##

wherein R is a C1 -C20 saturated group (preferably C1

-C12), p is between about 50 and about 1,500 (preferably between

about 100 and about 500) and a, d and x are the same as defined above with

respect to B and C. That is, a and d are any positive numbers (preferably,

a is between about 0 and about 100), and x is greater than 1 (preferably

between about 1 and about 100),

Examples of component (E) include

##STR8##

wherein p is between about 50 and about 1,500, and preferably, between

about 100 and about 500; s is between about 0.1 and about 50, and

preferably, between about 0.5 and about 20; t is between about 20 and

about 1,500, and preferably, between about 20 and about 500; w is between

about 20 about 1,500, and preferably between about 20 and about 500; and

Me, Ar and R have the same meanings as defined hereinabove.

In the compositions of the invention, it is contemplated that the amount of

component (A) should be between about 10 wt. % and 95 wt. % (preferably

between about 10 wt. % and 80 wt. %, most preferably between about 15 wt.

% and 35 wt. % ). The amount of component ( should be between about 0.1

wt. % and about 50 wt. % (preferably between about 0.4 wt. % and about 10

wt. %). The amount of component © should be between about 0.01 wt. % and

about 5.0 wt. % (preferably between about 0.01 wt. % and about 1.0 wt. %,

and most preferably between about 0.05 wt. % and about 0.5 wt. %). As

would be understood by someone having ordinary skill in the art, the

amounts of (A)-© expressed in terms of weight percents are relative to

each other.

If component (E) is optionally included, the amount of component (E) is

between about 30 wt. % and about 90 wt. % (preferably between about 70 wt.

% and about 85 wt. %). As would be understood by someone having ordinary

skill in the art, the amounts of (A), (, © and (E) expressed in terms

of weight percents are relative to each other.

An example of a preferred composition of the invention is a composition

that comprises:

(A) a polydiorganosiloxane that contains at least two unsaturated

hydrocarbon groups per molecule and that is represented by the formula

R'--SiR2 --O(SiR2 --O)n --SiR2 --R'

wherein R is a C1 -C12 saturated group, R' is a C1

-C12 unsaturated group that can undergo a hydrosilation reaction, n

is between about 200 and about 2,000, and the amount of (A) is between

about 10 wt. % and 80 wt. %;

( a polyorganohydrosiloxane that has at least three Si--H bonds per

molecule and is represented by the formula

##STR9##

wherein R is a C1 -C12 saturated group, x is between about one

and about 100, y is at least three, the sum of e and g is at least three,

a is between about 0 and about 100, c,d,e,f, and g are positive numbers,

and the amount of ( is between about 0.4 wt. % and about 10 wt. %;

© a compound that has at least one --SiH3 group, represented by the

formula

R4 (SiH3)k,

H3 Si(CH2)u SiH3,

Ar(SiH3)m,

H3 SiOSiR35,

H3 SiO(SiR25 O)a SiH3

or

H3 SiO(SiR25 O)SiR35,

wherein R4 a C3 -C20 hydrocarbon group, R5 is a

C1 -C20 hydrocarbon group, Ar is an aryl ring, k and m are at

least one, u is between about one and about 20, a is any positive number,

and the amount of © is between about 0.01 wt. % and about 5.0 wt. %;

(D) an effective amount of hydrosilation catalyst; and

(E) a polydiorganosiloxane compound that is represented by the formula

##STR10##

wherein R is a C1 -C12 saturated group, p is between about 50

and about 1,500 and a, d and x are the same as defined above with respect

to B and C. That is, a and d are any positive numbers (preferably, a is

between about 0 and about 100), and x is greater than 1 (preferably

between about 1 and about 100), and the amount of (E) is between about 30

wt. % and about 90 wt. %;

wherein the amounts of (A), (, © and (E) are relative to each other.

Various temporary catalyst inhibitors, component (F), can be optionally

included with component (D) in order to increase the storage stability and

working time of the polyorganosiloxane composition prior to curing.

Acetylenic alcohols such as 2-methyl-3-butyn-2-ol are described for such

purpose in U.S. Pat. No. 3,445,420; cyclic methylvinylsiloxanes in U.S.

Pat. No. 3,989,667; alkynyl silanes in U.S. Pat. No. 4,472,562; conjugated

enynes in U.S. Pat. No. 4,472,563; and maleate esters in U.S. Pat. No.

4,256,870. A complete listing is published in B Marciniec, Comprehensive

Handbook on Hydrosilylation, Pergamon Press, NY 1992, p. 190. The complete

disclosure of each of these references is incorporated herein by

reference.

In the present invention, the SiH3 -containing adhesion promoting

crosslinker © can also act as a temporary catalyst inhibitor.

Mixtures of adhesion promoters and work time extenders can be employed

advantageously for improved performance and processing of the curable

polysiloxane composition, as known to the person having ordinary skill in

the art. For example, methylvinylcyclosiloxanes, dialkylmaleates or

alkynols can be combined with the SiH3 -containing compounds of this

invention.

One of ordinary skill would be aware how best to optimize mixtures to

obtain particularly desired results. For instance, it may be desirable to

combine diethylmaleate with the primary silane to obtain extended

pot-life, enhanced adhesion to substrate and shortened cure time at

temperatures>80° C. Longer cure times, extended pot-life and

enhanced adhesion can be obtained with combinations of primary silanes and

methylvinylcyclosiloxanes. These conditions may be desirable if the

formulation must flow into and fill cavities at moderate temperatures

prior to crosslinking.

**************Get fantasy football with free live scoring. Sign up for FanHouse Fantasy Football today. (http://www.fanhouse.com/fantasyaffair?ncid=aolspr00050000000020)