A composition comprising (A) at least one mercapto-functional organosilicon compound having an average of a least two mercapto groups per molecule and (B) a cure initiator. The mercapto-functional organosilicon compound may include mercapto-functional organosilanes, mercapto-functional organosiloxanes, and mercapto-functional copolymers. The compositions of the present invention polymerize or cure to form compositions comprising reaction products of components (A) and (B). The cure initiator is a metal salt that produces a uniform cure throughout the composition, regardless of the amount of oxygen present. The cured products range in properties from soft gels to though elastomers to hard resins and are useful as molded articles, electrical encapsulants, and sealants.

FIELD OF THE INVENTION 
The present invention relates to compositions comprising a 
mercapto-functional organosilicon compound and a cure initiator. This 
invention also relates to compositions comprising a reaction product of a 
mercapto-functional organosilicon compound and a cure initiator. 
BACKGROUND OF THE INVENTION 
Oxygen-curable compositions comprising mercapto-functional compounds are 
known in the art. For example, U.S. Pat. No. 4,267,296 to Homan discloses 
oxygen-curable compositions obtained by mixing, substantially in the 
absence of oxygen, at least one mercapto-functional organosilicon-organic 
copolymer; a mixture of at least two different types of components 
selected from the group consisting of at least one organosilicon-organic 
copolymer, at least one mercapto-functional organic compound, and at least 
one mercapto-functional organosilicon compound; at least one filler; a 
catalytic amount of an iron carbonyl catalyst; and a proton donor acid 
that is compatible with the mixed composition and has a dissociation 
constant in aqueous solution greater than 10.sup.-5. 
U.S. Pat. No. 4,239,674 to Homan et al. teaches oxygen-curable 
mercaptoorganosiloxane compositions obtained by mixing, substantially in 
the absence of oxygen, at least one mercapto-functional organosiloxane 
having an average of at least two mercapto-functional siloxane units per 
molecule; optionally, a filler; and a catalytic amount of a cobaltocene. 
U.S. Pat. No. 4,252,932 to Homan et al. discloses oxygen-curable 
mercaptoorganosiloxane compositions formed by mixing, substantially in the 
absence of oxygen, at least one mercapto-functional organosiloxane having 
an average of at least two mercapto-functional siloxane units per 
molecule; optionally, at least one filler; and a catalytic amount of a 
metal carbonyl compound. 
Peroxide-curable compositions comprising mercaptoorganopolysiloxanes are 
also known in the art. For example, U.S. Pat. No. 4,279,792 to Homan et 
al. teaches compositions prepared by mixing a mercaptoorganopolysiloxane 
having an average of greater than two mercapto-containing siloxane units 
per molecule; a stannous salt of carboxylic acid having the formula 
Sn(OR.sup.1).sub.2 wherein R.sup.1 is a monovalent acyl radical; and 
optionally, an organic peroxide and/or a filler. 
U.S. Pat. No. 4,039,505 to Homan et al. discloses siloxane elastomers 
containing sulfur prepared by mixing a polydimethylsiloxane consisting 
essentially of methylvinylsiloxane units; a mercaptoorganopolysiloxane 
having an average of at least two sulfur containing siloxane units per 
molecule; an organic peroxide; and, optionally a filler. 
However, the prior art does not disclose compositions comprising at least 
one mercapto-functional organosilicon compound and a cure initiator, which 
cure uniformly regardless of the amount of oxygen present. 
SUMMARY OF THE INVENTION 
The present invention is directed to a composition comprising: 
(A) 100 parts by weight of at least one mercapto-functional organosilicon 
compound having an average of at least two mercapto groups per molecule; 
and 
(B) 0.5 to 50 parts by weight of a cure initiator. 
The present invention is also directed at a composition comprising a 
reaction product of (A) and (B), wherein (A) and (B) are as defined above. 
The compositions of the present invention offer numerous advantages over 
conventional oxygen-curable and peroxide-curable organosilicon 
compositions. Oxygen-curable organosilicon compositions require 
stoichiometric amounts of oxygen to cure. Also, such compositions cure 
from the surface inward as a function of the ingress of oxygen. 
Unfortunately, oxygen transport through such compositions is retarded once 
a skin of cured material is formed at the surface. Consequently, these 
compositions are limited to a practical sample thickness of about 
one-quarter inch. Although, peroxide-curable compositions can be cured in 
the absence of oxygen at elevated temperatures, cure is typically very 
slow at moderate temperatures. Moreover, the rate of cure in compositions 
employing peroxides is often difficult to control. By contrast, the 
organosilicon compositions of the instant invention cure uniformly at a 
controllable rate throughout their entire depths regardless of the amount 
of oxygen initially present in the compositions or the permeability of the 
compositions to oxygen. Consequently, the compositions of the present 
invention can be used to prepare deep section samples having a thickness 
greater than two inches. 
The cure initiators used in the compositions of the present invention 
provide adequate working time and a rapid deep section cure at room 
temperature or mildly elevated temperatures. The compositions of the 
present invention also exhibit a prolonged shelf life when kept cold. 
Unlike the trace catalysts used in conventional compositions, the cure 
initiators of the present invention are not easily inhibited. Moreover, 
the cure rate can be tailored over an extremely wide range by varying the 
temperature and/or the cure initiator concentration. 
The compositions of this invention cure to form products ranging in 
properties from soft gels to tough elastomers to hard resins. These 
products are useful as molded articles, electrical encapsulants, and 
sealants. 
DETAILED DESCRIPTION OF THE INVENTION 
Component (A) of the present invention is at least one mercapto-functional 
organosilicon compound having an average of at least two mercapto groups 
per molecule. The term "mercapto-functional" is used herein to indicate 
the presence of a mercapto group, --SH, in an organosilicon compound. 
Preferred mercapto-functional organosilicon compounds include 
mercapto-functional organosilanes, mercapto-functional organosiloxanes, 
and mercapto-functional copolymers. 
Mercapto-functional organosilanes useful in the compositions of the present 
invention have an average of at least two mercapto groups per molecule and 
are free of aliphatic unsaturation and functional groups that are reactive 
with mercapto groups at room temperature, such as epoxy and isocyanate. 
Preferably, the mercapto-functional organosilane has the general formula 
EQU [(HS).sub.v Z].sub.w SiR.sub.4-w 
In the preceding formula for the mercapto-functional organosilane, Z is a 
divalent or polyvalent hydrocarbon group free of aliphatic unsaturation, 
the valence of Z is v+1, R is a monovalent hydrocarbon group free of 
aliphatic unsaturation or OR.sup.1, R.sup.1 is alkyl having 1 to 4 carbon 
atoms, subscript v has a value of at least 1, subscript w has a value of 
from 1 to 3, and the sum v+w has a value of at least 3. 
For example, Z can be a divalent hydrocarbon group such as ethylene, 
propylene, 2-ethylhexylene, octadecylene, cyclohexylene, phenylene or 
benzylene; a trivalent hydrocarbon group such as 1,2,4-butanetriyl; or a 
polyvalent hydrocarbon group such as 
##STR1## 
Preferably, Z is a divalent aliphatic hydrocarbon group having 2 to 4 
carbon atoms. R is exemplified by, but not limited to alkyl such as 
methyl, ethyl, propyl, isopropyl, butyl, isobutyl, octyl, and octadecyl; 
cylcoalkyl such as cyclopentyl and cyclohexyl; and aryl such as phenyl, 
benzyl and naphthyl. R can also be OR.sup.1 where R.sup.1 is alkyl having 
1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, 
or isobutoxy. Preferably, R is alkyl having 1 to 4 carbon atoms or 
OR.sup.1. 
Mercapto-functional organosilanes useful in the compositions of the present 
invention include, but are not limited to, organosilanes such as Me.sub.2 
Si(CH.sub.2 CH.sub.2 CH.sub.2 SH).sub.2, Me.sub.2 Si(CH.sub.2 CHCH.sub.3 
CH.sub.2 SH).sub.2, (CH.sub.3 CH.sub.2).sub.2 Si(C.sub.6 H.sub.5 
SH).sub.2, (HSCH.sub.2 CH.sub.2 CH.sub.2).sub.3 SiMe, HSCH.sub.2 
CH(SH)CH.sub.2 CH.sub.2 Si(OMe).sub.3 and (HSCH.sub.2 CH.sub.2 
CH.sub.2).sub.2 Si(OMe).sub.2 where Me is met (CH.sub.3). Methods for the 
preparation of mercapto-functional organosilanes are well known in the 
art. For example, methods for the preparation of mercapto-functional 
organosilanes useful in the present invention are disclosed in Gawrys and 
Post, The Preparation of Certain Carbon-Functional Silathiols and Silathio 
Esters, Journal of Organic Chemistry, Vol. 27, p. 634ff. (1962) and U.S. 
Pat. No. 4,082,790, which are hereby incorporated by reference. 
Mercapto-functional organosiloxanes useful in the compositions of the 
present invention have an average of at least two mercapto groups per 
molecule and are free of aliphatic unsaturation and functional groups that 
are reactive with mercapto groups at room temperature, such as epoxy and 
isocyanate. The mercapto-functional organosiloxanes can be disiloxanes, 
trisiloxanes, or polysiloxanes. The polysiloxanes generally have a 
number-average molecular weight of less than 500,000. The mercapto groups 
can be located at pendant (internal),terminal, or pendant and terminal 
positions in the mercapto-functional organosiloxane. Preferably, the 
mercapto-functional organosiloxane contains siloxane units independently 
selected from the group consisting of 
##STR2## 
In the preceding formulae for the mercapto-functional siloxane units, 
R.sup.2 is R.sup.4 or OR.sup.1, R.sup.4 is alkyl having 1 to 4 carbon 
atoms or phenyl, R.sup. is alkyl having 1 to 4 carbon atoms, R.sup.3 is 
R.sup.2 or 3,3,3-trifluoropropyl, subscript n has a value of from 2 to 4, 
subscript a has a value of from 1 to 2, subscript b has a value of from 0 
to 2, subscript c has a value of from 0 to 1, subscript d has a value of 
from 0 to 3, and the sum a+b has a value of from 1 to 3. 
R.sup.2 can be R.sup.4, which is exemplified by methyl, ethyl, propyl, 
isopropyl, butyl, isobutyl, or phenyl. R.sup.2 can also be OR.sup.1 where 
R.sup.1 is alkyl having 1 to 4 carbon atoms, such as methoxy, ethoxy, 
propoxy, isopropoxy, butoxy, or isobutoxy. 
The mercapto-functional siloxane units which have the average unit formula 
##STR3## 
include, but are not limited to, the following: 
EQU HSC.sub.n H.sub.2n SiO.sub.3/2, 
##STR4## 
wherein R.sup.4, R.sup.1 and n are as defined above and n preferably has a 
value of 3. The mercapto-functional substituents present in the form of 
HSC.sub.n H.sub.2n can be, for example, 2-mercaptoethyl, 3-mercaptopropyl, 
3-mercaptobutyl, and 3-mercapto-2-methylpropyl. The mercapto-functional 
substituent can also be 2-mercapto-1,4-butane-diyl where both ends of the 
radical are attached to the same silicon atom. 
The siloxane units which have the average formula R.sup.3 SiO.sub.(4-d)/2 
include, but are not limited to, SiO.sub.04/2 units; monosubstituted units 
such as monomethylsiloxane units, monoethylsiloxane units, 
monopropylsiloxane units, monobutylsiloxane units, and monophenylsiloxane 
units; disubstituted units such as dimethylsiloxane units, diethylsiloxane 
units, diphenylsiloxane units, phenylmethylsiloxane units, 
methylbutylsiloxane units, phenylethylsiloxane units, 
3,3,3-trifluoropropylmethylsiloxane units, and methylisopropylsiloxane 
units; and trisubstituted units such as trimethylsiloxane units, 
phenyldimethylsiloxane units, triethylsiloxane units, 
diphenylmethylsiloxane units, diphenylisopropylsiloxane units, 
3,3,3-trifluoropropyldimethylsiloxane units, diphenylbutylsiloxane units 
and triphenylsiloxane units. 
Mercapto-functional organosiloxanes useful in the compositions of the 
present invention include mercaptopolydiorganosiloxanes containing 
terminal R.sub.3.sup.4 SiO.sub.1/2 siloxane units and mercapto-functional 
siloxane units selected from the group consisting of 
##STR5## 
any remaining siloxane units having the formula R.sub.2.sup.4 SiO.sub.2/2, 
wherein R.sup.4 and n are defined above, and the number-average molecular 
weight of the mercaptopolydiorganosiloxane is less than 500,000. 
Preferably, R.sup.4 is methyl, n is 3, and the number-average molecular 
weight of the mercaptopolydiorganosiloxane is less than 100,000. 
Mercapto-functional organosiloxanes useful in compositions of the present 
invention also include mercaptopolydiorganosiloxanes having 
mercapto-functional siloxane units selected from the group consisting of 
EQU HSC.sub.n H.sub.2n (R.sup.4).sub.2 SiO.sub.1/2, HSC.sub.n H.sub.2n (R.sup.1 
O).sub.2 SiO.sub.2/2, 
##STR6## 
any remaining siloxane units being R.sub.2.sup.4 SiO.sub.1/2, wherein 
R.sup.4, R.sub.1 and n are defined above and the number-average molecular 
weight of the mercaptopolydiorganosiloxane is less than 500,000. 
Preferably, each R.sup.4 is methyl, n is 3, the mercapto-functional 
siloxane units are selected from the group consisting of 
EQU HSCH.sub.2 CH.sub.2 CH.sub.2 (CH.sub.3).sub.2 SiO,.sub.1/2 and 
##STR7## 
and the number average molecular weight of the 
mercaptopolydiorganosiloxane is less than 100,000. 
Mercapto-functional organosiloxanes useful in compositions of the present 
invention further include mercaptopolydiorganosiloxanes having both 
pendant and terminal mercapto groups. Such mercaptopolydiorganosiloxanes 
contain two mercapto-functional siloxane units selected from the group 
consisting of 
EQU (HSC.sub.n H.sub.2n,)R.sub.2.sup.4 SiO.sub.1/2, (HSC.sub.n 
H.sub.2n)(R.sup.1 O).sub.2 SiO.sub.1/2, 
##STR8## 
and at least one mercapto-functional siloxane unit selected from the group 
consisting of siloxane units of the formula 
EQU (HSC.sub.n H.sub.2n)R.sup.4 SiO.sub.2/2 and 
##STR9## 
any remaining siloxane units having the formula R.sub.2.sup.4 SiO.sub.2/2, 
wherein R.sup.4, R.sup.1 and n are defined above and the number-average 
molecular weight of the mercaptopolydiorganosiloxane is less than 500,000. 
Preferably, each R.sup.4 is methyl, n is 3, the terminal 
mercapto-functional siloxane units are selected from the group consisting 
of HSCH.sub.2 CH.sub.2 CH.sub.2 (CH.sub.3).sub.2 SiO.sub.1/2 and 
##STR10## 
and the mercaptopolydiorganosiloxane has a number-average molecular weight 
of less than 100,000. 
Blends comprising two or more of the preceding 
mercaptopolydiorganosiloxanes can also be used in the compositions of the 
present invention to obtain products ranging in properties from soft gels 
to tough elastomers to hard resins. For example, the compositions in 
Example 2, which contains a mercaptopolydiorganosiloxane having the 
formula HSPrMe.sub.2 Si(OSiMe.sub.2).sub.1030 OSiMe.sub.2 PrSH and a 
mercaptopolydiorganosiloxane having the formula Me.sub.3 
Si(OSiMe.sub.2).sub.749 (OSiMePrSH).sub.6 OSiMe.sub.3, where Pr is propyl 
and Me is methyl, cures to form a tough, low modulus elastomer. 
The methods for preparing the above mercaptopolydiorganosiloxanes are 
well-known in the art. One method for making a 
mercaptopolydiorganosiloxane containing HSC.sub.n H.sub.2n 
(R.sup.4)SiO.sub.2/2 siloxane units and R.sub.3.sup.4 SiO.sub.1/2 siloxane 
units is taught by Viventi in U.S. Pat. No. 3,346,405. Another method is 
taught by Bokerman et al. in U.S. Pat. No. 4,133,939. For example, Example 
1 of the Bokerman, et al, patent teaches the production of a 
mercaptopolydiorganosiloxane which is a trimethylsiloxy-endblocked 
copolymer consisting of about 94 mole percent dimethylsiloxane units and 
about 5 mole percent 3-mercaptopropylmethylsiloxane units. Le Grow, in 
U.S. Pat. No. 3,655,713 teaches methods for making 
mercaptopolydiorganosiloxanes having pendant mercapto groups and 
mercaptopolydiorganosiloxanes containing terminal mercapto groups. 
Several methods for producing mercaptopolydiorganosiloxanes containing 
terminal HSC.sub.n H.sub.2n R.sub.2.sup.4 SiO.sub.1/2 siloxane units are 
known. One method involves the use of a disiloxane bearing a 
silicon-bonded mercaptoalkyl radical, such as sym-tetramethyl 
bis(3-mercaptopropyl)disiloxane, and a cyclic polydiorganosiloxane such as 
octamethylcyclotetrasiloxane. Appropriate amounts of the 
mercapto-functional disiloxane and cyclic polydiorganosiloxane are heated 
together with an acidic catalyst such as trifluoromethanesulfonic acid for 
3 to 8 hours. The mixture is then neutralized and the mercapto-terminated 
polydiorganosiloxane is recovered. 
Mercaptopolydiorganosiloxanes having both pendant and terminal mercapto 
groups can be prepared using the procedures outlined above for producing 
mercaptopolydiorganosiloxanes having terminal mercapto siloxane units by 
adding a cyclic mercaptopolydiorganosiloxane such as [HSCH.sub.2 CH.sub.2 
CH.sub.2 (CH.sub.3)SiO].sub.4 to the reaction mixture to introduce pendant 
mercapto groups into the polymer. Likewise, mercaptopolydiorganosiloxanes 
containing both pendant and terminal mercapto groups can be prepared using 
the procedures outlined above for producing mercaptopolydiorganosiloxanes 
having pendant mercapto groups by substituting terminal 
mercapto-functional siloxane units, which can be introduced in the form of 
a disiloxane such as sym-tetramethyl bis(3-mercaptopropyl)disiloxane, in 
place of non-functional endblocking units in the reaction mixture. 
Cyclic mercaptopolydiorganosiloxanes can be prepared by various methods, 
one of which involves preparing the corresponding chloroalkylsilane, such 
as 3-chloropropylmethyldichlorosilane, and hydrolyzing the silanes to form 
a mixture of linear and cyclic polydiorganosiloxanes. If desired, the 
ratio of cyclic to linear polydiorganosiloxanes can be altered by heating 
in the presence of an acidic catalyst for a period of time, during which 
time a portion of the cyclic polydiorganosiloxanes formed are removed by 
distillation to shift the equilibrium of the reaction in the direction 
which favors the formation of cyclic polydiorganosiloxanes. Then, for 
example, Viventi teaches that the chloroalkyldiorganosiloxanes can be 
reacted with sodium sulfohydride to produce mercaptopolydiorganosiloxanes. 
Mercapto-functional silanes containing alkoxy groups such as 
3-mercaptopropylmethyldimethoxysilane can also be hydrolyzed at about 
40.degree.-50.degree. C. in the presence of an acidic catalyst and 
vacuum-stripped at 120.degree. C. to remove alcohol and other undesirable 
volatile materials. Such mixtures can also be referred to as, for example, 
the 3-mercaptopropylmethyl hydrolyzate of 
3-mercaptopropylmethyldimethoxysilane. Other means for preparing cyclic 
mercaptopolydiorganosiloxanes will be apparent to persons skilled in the 
art. 
The production of mercapto-functional organosiloxane resins by the partial 
hydrolysis of mixtures of silanes such as HSC.sub.n H.sub.2n 
Si(OR.sub.1).sub.3 and R.sub.2.sup.4 Si(OR.sup.1).sub.2 is demonstrated by 
the Viventi patent. Likewise, mercapto-functional organosiloxane resins 
result when a sufficient number of siloxane units such as R.sup.4 
SiO.sub.3/2 are present in the mercaptoorganosiloxanes taught in the Le 
Grow patent. The Viventi, Le Grow and Bokerman, et al, patents are hereby 
incorporated by reference to teach the production of 
mercaptoorganosiloxanes useful in compositions of the present invention. 
Mercaptopolydiorganosiloxanes which contain terminal siloxane units of the 
formula 
##STR11## 
can be prepared by reacting a hydroxyl-terminated polydiorganosiloxane and 
a (mercaptoalkyl)trialkoxysilane of the formula 
EQU HSC.sub.n H.sub.2n Si(OR.sup.1).sub.3 
in the presence of solid potassium hydroxide or a potassium silanolate 
catalyst. The potassium silanolate catalyst is preferred for higher 
viscosity polydiorganosiloxanes. The (mercaptoalkyl)trialkoxysilane is 
preferably used in an excess of about 10 mole percent over stoichiometric 
amounts. The resulting product is essentially a polydiorganosiloxane 
endblocked with units of the formula 
##STR12## 
There may be some small amount of units wherein two SiOH groups have 
reacted with one (mercaptoalkyl)trialkoxysilane molecule, but the amount 
is small enough that the character of the endblocked polydiorganosiloxane 
is not noticeably altered. 
Mercapto-functional copolymers useful in the compositions of the present 
invention contain both silicon-free organic segments and organosiloxane 
segments. The copolymers have an average of at least two mercapto groups 
per molecule and are free of aliphatic unsaturation and functional groups 
that are reactive with mercapto groups at room temperature, such as epoxy 
and isocyanate. For example, copolymers containing both organosilicon 
segments and segments such as organic polyurethane or organic polysulfide 
are taught in Canadian Pat. Nos. 783,649 and 911,098. In U.S. Pat. No. 
3,445.419, Vanderlinde teaches the production of a mercapto-functional 
organosiloxane which can be classified as a graft copolymer. The three 
immediately preceding patents are hereby incorporated by reference to 
teach the production of mercapto-functional copolymers useful in the 
compositions of the present invention. 
Component (A) of the present invention can also be a mixture comprising 
different mercapto-functional organosilanes, different mercapto-functional 
organosiloxanes, different mercapto-functional copolymers, or mixtures of 
the any of the above. The various combinations possible are readily 
apparent to one skilled in the art and include compounds in varying 
proportions having different molecular weights, differing mercapto groups, 
and varying amounts of mercapto groups. When mixtures are used, the 
components should be sufficiently compatible with one another to produce a 
composition which does not undergo appreciable separation upon storage. 
Component (B) of the present invention is a cure initiator which initiates 
and participates in the cure reaction. The compositions of the present 
invention polymerize or cure to form compositions comprising a reaction 
product of components (A) and (B). The compositions cure predominately by 
the formation of disulfide (--S--S--) bonds. The cure initiator produces a 
uniform cure throughout the composition regardless of the amount of oxygen 
available. The cure initiator can be any metal salt capable of 
participating in an oxidation-reduction reaction substantially in the 
absence of oxygen with the mercapto groups in component (A) to form 
disulfide bonds. Cure initiators suitable for use in the present invention 
include salts of cooper(II), tin(IV), and mercury(I). The various salts of 
a given metal differ in their ability to initiate and participate in the 
cure reaction. However, the effectiveness of a particular metal salt in 
effecting cure under oxygen-free conditions can be easily determined by 
routine experimentation using the methods set forth in Example 5. 
Preferably, the cure initiator is selected from the group consisting of 
copper(II) acetylacetonate, copper(II) acetate, copper(II) carbonate 
basic, copper(II) chloride, dibutyltin dibutoxide, dibutyltin dilaurate, 
and mercury(I) chloride. More preferably, the cure initiator is selected 
from the group consisting of copper(II) acetylacetonate, copper(II) 
acetate, copper(II) carbonate basic, copper(II) chloride, and dibutyltin 
dibutoxide. Most preferably, the cure initiator is copper(II) 
acetylacetonate, also represented hereinafter by the formula 
Cu(acac).sub.2 where acac is acetylacetonate. When Cu(acac).sub.2 is used 
as a cure initiator in the compositions of the present invention, acetyl 
acetone (2,4-pentanedione) is evolved during the cure process. The cure 
initiator can be a single metal salt or a mixture of two or more of the 
metal salts described above. 
The amount of component (B) present in the compositions of the present 
invention is typically from 0.5 to 50 parts by weight per 100 parts by 
weight of the mercapto-functional organosilicon compound. Preferably, 
component (B) is present in an amount from 1 to 25 parts by weight, and 
more preferably from 1 to 10 parts by weight per 100 parts by weight of 
component (A). The cure rate of a composition of the present invention is 
dependent on the concentration of component (B). Generally, cure rate 
increases as the concentration of reaction initiator increases within the 
ranges specified above. 
Fillers may be used with the compositions of this invention, but are not 
required. Extending fillers are typically used in an amount from 1 to 200 
parts by weight per 100 parts by weight of mercapto-functional compound 
(A). Suitable extending fillers include titanium dioxide, calcium 
carbonate, talc, clay, ground or crushed quartz, diatomaceous earth, 
fibrous fillers such as glass or asbestos, and the like. Calcium carbonate 
is a preferred extending filler in the compositions of the present 
invention. Reinforcing fillers may also be used, such as fumed silica, 
surface-treated fumed silica, precipitated silica, surface-treated 
precipitated silica, and carbon black. Fumed silica and precipitated 
silica, treated or untreated, are preferred reinforcing fillers. Other 
additives such as coloring pigments, fire-retarding compounds and the like 
are also contemplated as being useful in the present invention. Because 
the activity of the cure initiator may be affected by water, it is 
preferred that any fillers or additives be substantially free of water. 
The effects of fillers and additives on shelf life can be determined by 
routine testing. 
In general, the compositions of the present invention can be prepared by 
blending the components (A) and (B) in any order. Preferably, a 
one-package product is prepared by adding a dispersion of the cure 
initiator (B) to at least one merecapto-functional compound (A) and any 
filler or additives. Component (B) can be dispersed in a solvent or 
diluent such as toluene, mineral oil or trimethylsiloxy-terminated 
polydimethylsiloxane fluid. Preferably, the mercapto-functional compound 
and reaction initiator are combined at a temperature below about 
30.degree. C. to prevent immediate reaction of the components and thus 
ensure adequate working time. Low-shear mixers can be used for lower 
viscosity compositions while high-shear sigma blade mixers can be used for 
more viscous compositions such as sealant formulations containing filler. 
Compositions prepared at room temperature should be used immediately after 
mixing. However, the shelf life of the compositions of this invention can 
be extended to several months by storing the mixtures at a temperature of 
-20.degree. C. or below. 
Alternatively, a convenient two-package product can be prepared by 
combining all of component (A) with part or all of any filler or additive 
in one package and any remaining filler or additive with all of component 
(B) in another package. Preferably, the components are packaged in such as 
manner that equal weight amounts of each package can be mixed to produce 
the compositions of this invention. Individual sealed packages can be 
stored for over 6 months at ambient conditions without any deterioration 
in the performance of the composition produced upon their admixture. 
The compositions of the present invention polymerize or cure to form 
compositions comprising a reaction product of components (A) and (B). The 
compositions are cured at a temperature of from room temperature to 
150.degree. C., preferably from room temperature to 100.degree. C., and 
more preferable from room temperature to 50.degree. C. At temperatures 
substantially below room temperature, several days may be required to 
achieve a full cure. At temperatures above 150.degree. C. in an enclosed 
environment, gas evolution is restricted and bubbles may become entrapped 
in the cured materials. Deep section samples measuring one inch in depth 
and 1.5 inches in diameter can be cured completely in about 24 hours at 
room temperature or in about 35 minutes at 50.degree. C. Room temperature 
polymerization or cure will be satisfactory for many applications, but 
heating can also be used to accelerate the rate of cure. 
The cured products of this invention can range in properties from soft gels 
to tough elastomers to hard resins. Physical properties such as durometer 
hardness are related to cross-link density. The crosslink density can be 
increased by increasing the number of mercapto groups in the 
mercapto-functional organosilicon compound. Generally, the higher the 
crosslink density, the harder the cured product will be when all other 
variables, such as types of substituents and structure, are kept constant. 
Compositions composed of organosilicon compounds that contain an average of 
only two mercapto groups per molecule, especially linear compounds, are 
generally only capable of polymerization by chain-extension and produce 
tacky gums unless the mercapto-functional compounds themselves are 
sufficiently cross-linked or are high enough in molecular weight to result 
in a tack free surface after cure. Compositions containing an average of 
more than two mercapto groups per molecule are capable of polymerizing to 
from three-dimensional networks which can range from soft gels to hard 
resins, depending on the crosslink density.

EXAMPLES 
The following examples are presented to further illustrate the compositions 
of this invention, but are not to be considered as limiting the invention, 
which is properly delineated in the appended claims. The compositions were 
prepared in the presence of air unless otherwise indicated. All parts and 
percentages reported in the examples are by weight. The following methods 
and materials were employed: 
The mercapto (SH) content of a polymer was determined by reacting a sample 
with excess iodine and back titrating with sodium thiosulfate to the 
starch endpoint. 
The hydroxyl content of a polymer was determined by Fourier transform 
infrared (FTIR) spectrometry using a Nicolet 605X spectrometer. The 
polymer samples were dissolved in carbon tetrachloride. 
Number-average and weight-average molecular weights (M.sub.n and M.sub.w) 
were determined by gel permeation chromatography (GPC) using Varian TSK 
4000+2500 columns at 35.degree. C., a chloroform mobile phase at 1 mL/min, 
and a refractive index detector. Polystyrene standards were used for 
linear regression calibrations. 
Viscosity of a polymer was determined at room temperature 
(23.degree..+-.2.degree. C.) using a Brookfield Type B rotating disc 
viscometer equipped with a no. 5 spindle. 
Volatile content of a polymer preparation was determined by heating a 5 
gram sample of the material at 110.degree. C. for 16 hours and determining 
the weight loss. 
Thermal stability of a polymer was determined by thermal gravimetric 
analysis (TGA) using a Dupont 952 analyzer. Samples were heated from room 
temperature to 300.degree. C. at 10.degree. C./min in an air atmosphere. 
The resultant mass loss for each polymer was determined from the 
thermogram. 
Tensile strength, elongation, and flexural modulus measurements were 
performed in accordance with ASTM D 412C using a tensiometer. Tensile 
strength and elongation measurements were carried out by taking the 
samples to ultimate failure. The modulus values refer to secant modulus at 
100% elongation. Tear measurements were performed in accordance with ASTM 
D 624 using a tensiometer equipped with die B. 
Plasticity was measured with a Scott Tester (Scott Tester Inc., Providence, 
R.I. using circular samples having a diameter of 14 mm and a thickness of 
8 mm. 
Hardness was measured with a Durometer Type 00 instrument using a sample 
having a thickness of 3 mm. 
Skin-over time (SOT) was determined by noting the time required for the 
formation of a skin on the surface of a composition. Tack-free time (TFT) 
of a composition was determined in accordance with ASTM C-679. Tack-free 
time indicates when the composition is tack-free to touch with a 
polyethylene strip. 
Finger tack is a subjective evaluation, which was determined by touching 
the surface of the cured composition to determine the degree of 
"stickyness" thereof. 
The low density polyethylene SemKit.RTM. tube (Semco, Inc., Glendale, 
Calif.) employed in the Examples is a cylinder having the appearance of a 
tube commonly used for caulking compounds. The tube contains a means for 
introducing the components of a composition and stirring the contents. The 
tube can also be placed in a vacuum for removal of volatile materials from 
the composition therein. 
Example 1 
This example shows how to prepare the mercapto-functional compounds used in 
the compositions set forth below. 
Mercaptopolydiorganosiloxane (1A) 
HSPrMe.sub.2 Si(OSiMe.sub.2).sub.1030 OSiMe.sub.2 PrSH was prepared by 
mixing 1140 g of a mixture of cyclosiloxanes having the average formula 
(Me.sub.2 SiO).sub.4 and 4.23 g of (HSPrSiMe.sub.2).sub.2 O in a two 
liter, three-neck round bottom flask equipped with a stirrer, condenser, 
thermometer and nitrogen blanket. The mixture was heated to 74.degree. C., 
and then 0.14 mL (0.24 g) of trifluoromethanesulfonic acid was added via 
syringe. The mixture was stirred for 21.5 hours and then was allowed to 
cool to room temperature. The cooled mixture was neutralized by adding 
24.6 g NaHCO.sub.3. The neutralized mixture was pressure-filtered (0.41 
MPa) through a 1.2 .mu.m acrylic copolymer membrane (Versapor.RTM. 1200 
filter, Gelman Scientific), which was supported on a Whatman No. 1 paper 
filter. The filtrate was stripped under vacuum (&lt;667 Pa, 160.degree. C. ) 
to obtain the desired polymer. SH=0.098%; OH=70 ppm; M.sub.w =95,220; 
M.sub.n =52,400; viscosity=42.24 Pa.s; volatiles=3.32%; mass loss 
(TGA)=4.12%. 
Mercaptopolydiorganosiloxane (1B) 
HSPrSiMe.sub.2 (OSiMe.sub.2).sub.799.6 (OSiMePrSH).sub.0.3 OSiMe,PrSH was 
prepared by mixing 994.6 g of a mixture of cyclosiloxanes having the 
average formula (Me.sub.2 SiO).sub.4, 0.68 g of a mixture of 
cyclosiloxanes having the average formula (HSPrSiMeO).sub.4, and 4.74 g of 
(HSPrSiMe.sub.2).sub.2 O in a two liter, three-neck round bottom flask 
equipped with a stirrer, condenser, thermometer and nitrogen blanket. The 
mixture was heated to 65.degree. C., and then 0.59 mL of 
trifluoromethanesulfonic acid was added via syringe. The mixture was 
stirred for 21.5 hours and then was allowed to cool to room temperature. 
The cooled mixture was neutralized by adding 5.9 g NaHCO.sub.3. The 
neutralized mixture was pressure-filtered (0.41 MPa) through a 1.2 .mu.m 
acrylic copolymer membrane (Versapor.RTM. 1200 filter, Gelman Scientific), 
which was supported on a Whatman No.1 paper filter. The filtrate was 
stripped under vacuum (&lt;667 Pa, 160.degree. C.) to obtain the desired 
polymer. SH=0.128%; OH=90 ppm; M.sub.w =82,040; M.sub.n =44,080; 
viscosity=29.33 Pass; volatiles=2.33%; mass loss (TGA)=1.23%. 
Mercaptopolydiorganosiloxane (1C) 
Me.sub.3 Si(OSiMe.sub.2).sub.749 (OSiMePrSH).sub.6 OSiMe.sub.3 was prepared 
by mixing 16.77 g of a mixture of cyclosiloxanes having the average 
formula (HSPrMeSiO).sub.4, 1176.52 g of a mixture of cyclosiloxanes having 
the average formula (MeSiO).sub.4, and 6.71 g Me.sub.3 
Si(OSiMe.sub.2).sub.2 OSiMe.sub.3 in a two liter, three-neck round bottom 
flask equipped with a stirrer, condenser, thermometer and nitrogen 
blanket. The mixture was heated to 65.degree. C. and then 0.76 mL 
trifluoromethanesulfonic acid was added via syringe. The mixture was 
stirred for 5 hours and then was allowed to cool to room temperature. The 
cooled mixture was neutralized by adding of 25.8 g NaHCO.sub.3. The 
neutralized mixture was pressure-filtered (0.41 MPa) through a 1.2 .mu.m 
acrylic copolymer membrane (Versapor.RTM. 1200 filter, Gelman Scientific), 
which was supported on a Whatman No.1 paper filter. The filtrate was 
stripped under vacuum (&lt;667 Pa, 160.degree. C.) to obtain the desired 
polymer. SH=0.47%; OH=90 ppm; M.sub.4 =68,060; M.sub.n =36,810; 
viscosity=11.52 Pa.s; volatiles=1.8%; mass loss (TGA)=2.25%. 
Example 2 
This example demonstrates the preparation of a composition employing 
copper(II) acetylacetonate as the cure initiator. A slurry of the cure 
initiator was prepared by mixing 10 parts of Cu(acac).sub.2 with 90 parts 
of toluene. A base was prepared by mixing 70 parts of polymer (1A), 30 
parts of polymer (1C), and 100 parts of pre-dried (110.degree. C., 18 
hours) stearic acid-treated CaCO.sub.3 (CS11.RTM., Georgia Marble 
Company). A composition was prepared by mixing 10 parts of the slurry of 
Cu(acac).sub.2 with 200 parts of the base. The composition contained 1 
part by weight of Cu(acac).sub.2 per 100 parts by weight of polymer. All 
mixing operations were carried out using a standard laboratory mixer. 
The composition was placed in a SemKit.RTM. tube and extruded onto three 
polyethylene sheets. The three samples (2a, 2b, and 2c) were spread with a 
flat blade laboratory spatula to thicknesses of 2 mm, 1 mm, and 1.9 mm, 
respectively, and allowed to cure at room temperature. The compositions 
exhibited a skin-over time of 2-2.5 hours and a tack-free time of 3-4 
hours. Table I shows the properties of the cured samples after 24 hours. 
TABLE 1 
______________________________________ 
Durometer 
Tensile 100% 
Hardness Strength Elongation Modulus 
Sample (Shore 00) (Mpa) (%) (Mpa) 
______________________________________ 
2a 70 0.38 734 0.24 
2b -- 0.48 935 0.14 
2c -- 0.35 889 0.12 
______________________________________ 
Example 3 
This example demonstrates the effect of temperature on the extent of cure 
for compositions containing copper(II) acetylacetonate. A slurry of 
Cu(acac).sub.2 in toluene and a base were prepared as described in Example 
2. The base was immediately deoxygenated by placing a SemKit.RTM. tube 
containing the base in a vacuum chamber and gradually reducing the 
pressure to 0.10 MPa. During the gradual evacuation process, the vacuum 
was periodically terminated and the chamber was subsequently back filled 
with dry nitrogen. This gradual process eliminated spillage of the base 
due to excessive foaming. After 18 hours at 0.10 MPa, the chamber was back 
filled with dry nitrogen and the tube was sealed. A composition was 
prepared by injecting the slurry of Cu(acac).sub.2 into the SemKit.RTM. 
tube (10 parts of slurry per 200 parts base) and mixing the contents. The 
composition contained 1 part by weight of Cu(acac).sub.2 per 100 parts by 
weight of polymer. The composition was extruded into low density 
polyethylene (LDPE) molds having a depth of 25.4 mm and diameter of 38.1 
mm. One sample (3a), designated the Control, was cured at room temperature 
and another sample (3b) was cured at 50.degree. C. A third sample (3c) was 
cured at room temperature for 6 hours, placed in a freezer at -25.degree. 
C. for 3.5 days, and then allowed to cure at room temperature. The 
skin-over time (SOT), tack-free time (TFT), and times required to reach 
Shore 00 hardness values of 30-40, 50-60, and 60-70 were determined for 
each sample. The results are displayed in Table II. 
Example 4 
This example demonstrates the effect of cure initiator concentration on the 
extent of cure for compositions containing copper(II) acetylacetonate. A 
slurry of Cu(acac).sub.2 and a base were prepared as described in Example 
2. The base was immediately deoxygenated according to the method in 
Example 3. A composition was prepared by injecting the slurry of 
Cu(acac).sub.2 into the SemKit.RTM. tube (20 parts of slurry per 200 parts 
base) and mixing the contents. The composition contained 2 parts by weight 
of Cu(acac).sub.2 per 100 parts by weight of polymer. The composition was 
extruded into a polyethylene mold having a diameter of 38.1 mm and a depth 
of 25.4 mm and allowed to cure at room temperature. The skin-over time 
(SOT), tack-free time (TFT), and times required to reach Shore 00 hardness 
values of 30-40, 50-60, and 60-70 were determined for the sample. The 
results for this sample (4) are compared to the Control sample (3a), which 
contained 1 part by weight of Cu(acac).sub.2 per 100 parts by weight of 
polymer, in Table II. 
Example 5 
This example demonstrates the deep section cure and effect of atmospheric 
oxygen on the extent of cure for compositions containing copper(II) 
acetylacetonate. A composition was prepared as described in Example 2, 
wherein the base was not deoxygenated. The composition was placed in a 
SemKit.RTM. tube and extruded into a polyethylene mold having a diameter 
of 38.1 mm and a depth of 25.4 mm and a allowed to cure at room 
temperature. The skin-over time (SOT), tack-free time (TFT), and times 
required to reach Shore 00 hardness values of 30-40, 50-60, and 60-70 were 
determined for the sample. The results for this sample (5) are compared to 
the Control sample (3a) in Table II. 
Another composition was prepared using deoxygenated base as described in 
Example 3, except the composition was stored at room temperature in a 
SemKit.RTM. tube under nitrogen. In the absence of air, the composition 
cured completely in 24 hours to form a tough rubber having a diameter of 
38.1 mm and a thickness of 50.8 mm. 
TABLE II 
__________________________________________________________________________ 
Extent of Cure.sup.3 
(hours to Shore 00) 
Cure Parts.sup.1 of 
SOT/ Initial 
Medium Full 
Sample Temp. Cu(acac).sub.2 Base.sup.2 TFT 00 = 30-40 00 = 50-60 00 = 
60-70 
__________________________________________________________________________ 
3a RT 1 D 2-3 h/ 
16-20 22-24 24-30 
Control 5-6 h 
3b 50.degree. C. 1 D &lt;50 min/ &lt;0.83 &lt;0.83 &lt;0.83 
&lt;50 min 
3c RT, -25.degree. C., 1 D -- .sup. 14.5-18.5.sup.4 -- .sup. 18.5-28.5.s 
up.4 
RT 
4 RT 2 D 3-4 h/ 5-7.5 7.5-11 12-20 
3-4 h 
5 RT 1 ND 2-3 h/ 16-20 22-24 24-30 
5-6 h 
__________________________________________________________________________ 
.sup.1 Parts by weight per 100 parts by weight of polymer. 
.sup.2 D = Deoxygenated, ND = Not Deoxygenated. 
.sup.3 Solid, removable sample, retains shape. 
.sup.4 Extent of cure determined during final room temperature cure. 
Example 6 
This example further demonstrates the use of Cu(acac).sub.2 as a cure 
initiator in compositions containing mercapto-functional organosiloxanes. 
A composition was prepared as describe in Example 2 except that polymer 
(1B) was substituted for polymer (1A). A sample of the composition was 
placed in a SemKit.RTM. tube, extruded on a polyethylene sheet, spread 
with a flat blade spatula to a thickness of 1.6 mm, and allowed to cure at 
room temperature for 18 hours. The composition exhibited a tensile 
strength of 0.55 Mpa, an elongation of 707%, and a modulus of 0.26 Mpa. 
Another composition was prepared using a mercaptopolydiorganosiloxane 
having the average formula Me.sub.3 SiO(Me.sub.2 SiO).sub.43 
(HSPrMeSiO).sub.5 SiMe.sub.3 and a viscosity of approximately 0.10 Pa.s at 
25.degree. C. This polymer was prepared as described for polymer (1C.) in 
Example 1 by adjusting the monomer ratio and reaction time. Five grams of 
the polymer, 5 g of pre-dried (110.degree. C., 18 hours) stearic 
acid-treated CaCO.sub.3 (CS11.RTM., Georgia Marble Company), and 1.13 g of 
Cu(acac).sub.2 powder were blended using a standard laboratory mixer. The 
composition contained 22.6 parts by weight of Cu(acac).sub.2 per 100 parts 
by weight of polymer. A sample of the composition was placed on a 
polyethylene sheet at room temperature and spread with a flat blade 
spatula to a thickness of 3 mm. The composition exhibited a skin-over time 
of less than 30 min and was uniformly cured in 18 hours. The sample was 
very brittle and dry, having a tensile strength of 0.45 Mpa and an 
elongation of 18%. 
A second sample of the immediately preceding composition was extruded into 
a polyethylene mold having a diameter of 38.1 mm and a depth of 25.4 mm 
and cured at 50.degree. C. The composition uniformly cured in less than 30 
minutes, producing a very dry, hard, crumbly rubber which was easily 
removed from the mold. The material had a Shore 00 hardness value of 
70-80. 
Example 7 
This example demonstrates the use of various metal salts as cure 
initiators. A slurry of each cure initiator was prepared by mixing 10 
parts of the initiator with 90 parts of toluene. The base was prepared by 
combining 70 parts of polymer (1A), 30 parts of polymer (1C), and 100 
parts of pre-dried (110.degree. C., 18 hours) stearic acid-treated 
CaCO.sub.3 (CS11.RTM., Georgia Marble Company). Ten compositions were 
prepared by mixing 10 parts of the slurry of each cure initiator with 200 
parts of the polymer base. The compositions contained 1 part by weight of 
cure initiator per 100 parts by weight of polymer. The compositions were 
placed in circular aluminum weigh pans (diameter=63 mm, height=13 mm) and 
allowed to cure at room temperature. The extent of cure was monitored by 
measuring skin-over time (SOT) and tack-free time (TFT) for each sample 
(7a-7j). The results are presented in Table III. 
TABLE III 
______________________________________ 
Finger 
Sample Cure Initiator SOT/TFT Tack 
______________________________________ 
7a copper(II) .about.2.5 h/ 
dry-slightly 
acetylacetonate 3-4 h sticky 
7b Dibutyltin &lt;5 min/ very sticky 
dibutoxide &lt;30 min 
7c Dibutyltin dilaurate 30-50 min/ very sticky 
19-33 days 
7d Mercury(I) chloride 5-13 days/ very sticky 
19-33 days 
7e Iron(III) oxide &gt;33 days/ -- 
&gt;33 days 
7f Copper(II) sulfate, &gt;33 days/ -- 
anhydrous &gt;33 days 
7g Copper(II) 1-5 days/ very sticky 
carbonate, basic 1-5 days 
7h Copper(II) acetate 1-5 days/ sticky 
5-13 days 
7i Copper(II) chloride &lt;24 h/ slightly 
1-5 days sticky 
7j Copper(II) chloride 13-19 days/ -- 
dihydrate &gt;33 days 
______________________________________ 
Example 8 
This example demonstrates the effect of post cure temperature on the cured 
products formed in Examples 3, 4, and 5. Samples 3a, 3b, 4, and 5 were 
each cut into five cubes (6.4 mm). One cube of each sample was exposed to 
the following conditions: room temperature for 3.5 days, 110.degree. C. 
for 3.5 days, 150.degree. C. for 3.5 days, 200.degree. C. for 3.5 days and 
boiling water for 1 day. The samples were allowed to cool to room 
temperature and the percent compression of each sample was measured using 
a plastometer. The results are shown in Table IV. 
TABLE IV 
______________________________________ 
Plasticity 
(% Compression) 
Post Cure 
Time Sample Sample Sample Sample 
Temperature (days) 3a 3b 4 5 
______________________________________ 
RT 3.5 76-78 79 77 78 
110.degree. C. 3.5 74-79 74-79 74-79 78 
150.degree. C. 3.5 78 79 73 76 
200.degree. C. 3.5 74 74 80 72 
Boiling water 1 80-84 80 85 81 
______________________________________ 
Example 9 
This example demonstrates the use of reinforcing silica fillers in the 
compositions of the present invention. A first base was prepared by mixing 
70 parts of polymer (1B) and 30 parts of polymer (1C). A second base was 
prepared by mixing 100 parts of the first base and 25 parts of 
hexamethlydisilazane-treated fumed silica (Aerosil.RTM. R812S, DeGussa). A 
third base was prepared by mixing 100 parts of the first base and 25 parts 
of hexamethlydisilazane-treated precipitated silica (Tullinox.RTM. HM100, 
Tulco). Each base was initially blended with a whip mixer and then further 
blended using a two-roll mill. Powdered Cu(acac).sub.2 (1 part by weight 
per 100 parts by weight of polymer) was added to each base during the 
final stages of mixing. A sample (100 grams) of each composition was 
pressed between stainless steel plates under a load of 13,600 Kg at room 
temperature for 2 minutes. The plates were then transferred to a hot press 
and maintained under a load of 13,600 Kg at 100.degree. C. for 30 minutes. 
The results for each sample (9a-9c) are presented in Table V. 
TABLE V 
______________________________________ 
Tensile 100% Tear 
Filler.sup.1 Strength Elongation Modulus Strength 
Sample (wt %) (MPA) (%) (MPA) (N/m) 
______________________________________ 
9a no filler 0.23 456 0.10 783 
9b fumed 3.8 1287 0.35 16,310 
silica 
(20%) 
9c precipitated 3.0 903 0.40 24,187 
silica 
(20%) 
______________________________________ 
.sup.1 Fillers treated with hexamethyldisilazane.