Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2000-02-17
2001-07-24
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S026000, C528S031000, C528S032000, C556S418000
Reexamination Certificate
active
06265514
ABSTRACT:
For which the following is a specification:
This invention pertains to curable organo-silicone compositions and a method of making them. In particular, this invention pertains to alkenyl-functional poly(siloxaneacrylates) with pendant oxycarbonylethyleneimino-containing organic groups. These poly(siloxane-acrylates) can be cured into elastomers which have low or minimal weep characteristics when exposed to power train oils.
BACKGROUND OF THE INVENTION
For many years the automotive industry has been faced with a problem in their silicone rubber based power train sealing gaskets called “weep”. Weep occurs due to a temperature dependency of the swell of silicone rubber in engine oil. Swell describes the tendency of an elastomer in contact with certain fluids to change in linear dimensions, as a function of time and temperature, as the fluids are adsorbed into the elastomer matrix. Silicone rubbers swell more at higher temperatures (T
2
) than at ambient temperature (T
1
). Upon cooling the extra oil which is taken up in going from ambient temperature to higher temperature is expelled out of the material, forming weep, allowing oil to pass through the gasket.
Blizzard et. al in U.S. Pat. No. 5,739,192 teach polysiloxane copolymers produced by a Michael Addition reaction between polysiloxanes containing amine functional groups and acrylates having hydrocarbon containing groups. However, this patent does not teach a method of making alkenyl-functional poly(siloxane-acrylates) which are curable via free radical and hydrosilylation methods.
Lo et. al in U.S. Pat. No. 4,698,406 teach a curable two-part silicone composition comprising (i) an amine-functional polyorganosiloxane and (ii) acryl-functional polyorganosiloxane selected from acryloxy, methacryloxy or acrylamide-functional polyorganosiloxanes. Components (i) and (ii) of the composition cure by a Michael-type addition to form a solid polyorganosiloxane resin or elastomer.
Pendant methacryl-functional siloxanes have been prepared by reacting pendant aminosiloxanes with difunctional acryl compounds in a Michael-type addition reaction. See for example Lee et al. in EP Pub. No. 230,242, and Griswold et al. in EP Pub. No. 274,699. Siloxanes containing functional methacrylate groups have recently gained importance, because they may be cured by UV irradiation rather than by thermal initiation.
The object of this invention is to make poly(siloxane-acrylate) elastomers with reduced weep when exposed to engine oil and fluids in automotive power trains. Another object of this invention is alkenyl-functional poly(siloxane-acrylates) which are curable to such poly(siloxane-acrylate) elastomers. Another object is a method of making the alkenyl-functional poly(siloxane-acrylates) with pendant oxycarbonylethyleneimino-containing organic groups using a Michael-type addition.
SUMMARY OF INVENTION
This invention is poly(siloxane-acrylate) elastomers with low weep characteristics. This invention provides a novel route using Michael addition chemistry to provide curable alkenyl-functional poly(siloxane-acrylates). The alkenyl-functional poly(siloxane-acrylates) of this invention are synthesized by initially making amine functional alkenyl-containing siloxanes by mixing and heating a polydiorganosiloxane, and amino-functional silane hydrolyzate, a vinyl organosiloxane, and a base equilibration catalyst. The amine functional siloxanes are then reacted by means of a Michael addition reaction with an acrylate at room temperature to form alkenyl-functional poly(siloxane-acrylates) with oxycarbonylethyleneimino-containing organic groups. The oxycarbonylethyleneimino-containing organic groups may also be referred to as polar organic groups.
The solubility parameters of the alkenyl-functional poly(siloxane-acrylates), when determined through dilute solution viscosity, ranges from 8.7 (cal/cm
3
)
½
, in the case where 11 mole percent of the repeat units in the copolymer contained polar organic groups to 9.2 (cal/cm
3
)
½
, when 53 mole percent contained polar organic groups.
Poly(siloxane-acrylate) elastomers are prepared by conventional silicone cure mechanisms such as a free-radical cure of the poly(siloxane-acrylates) using a suitable peroxide catalyst. These poly(siloxane-acrylate) elastomers show reduced swell as the mole percent of polar organic groups in the elastomer is increased. Poly(siloxane-acrylate) elastomers may also be prepared by a hydrosilylation cure using a hydrosilylation crosslinker and a platinum catalyst.
DETAILED DESCRIPTION OF INVENTION
This invention is poly(siloxane-acrylate) elastomers with low weep characteristics. These elastomers are formed by the steps of:
(A) forming an amine functional alkenyl-containing siloxane by reacting a mixture comprising:
(a) a polydiorganosiloxane,
(b) an amino-functional silane hydrolyzate,
(c) an alkenylorganosiloxane, and
(d) a base equilibration catalyst, then
(B) reacting, at about 23° C., the amine functional alkenyl-containing siloxane with an acrylate to form a curable alkenyl-containing poly(siloxane-acrylate) with oxycarbonylethyleneimino-containing organic groups and,
(C) curing the alkenyl-containing poly(siloxane-acrylate) to form an poly(siloxane-acrylate) elastomer.
The amount of swell of an elastomer in a given solvent is controlled by the energetics of the polymer solvent interaction which is contained in a polymer-solvent interaction parameter c, the crosslink density of the polymer matrix, and the number of dimensions in which the sample is constrained. The present inventors chose to reduce the swell by altering the solubility parameter of the silicone rubber by the addition of organic side groups on the siloxane chain. The organic side groups on a siloxane change the parameter c of the resulting cured polymer so that the amount of oil adsorbed at any given temperature is reduced.
Amine Functional Alkenyl-containing Siloxane
The polydiorganosiloxane component (a) can be either a cyclic or linear polydiorganosiloxane. If the polydiorganosiloxane is linear, it can have the formula R
2
3
SiO(SiR
1
2
O)
x
SiR
2
3
where x has an average value of from 0 to 15,000, R
1
is selected from the group consisting of a trifluoropropyl group, an alkyl chain of 1 to 4 carbon atoms, and a phenyl group, and R
2
is selected from the group consisting of an alkenyl group, a hydroxyl group, an alkoxy group, a trifluoropropyl group, an alkyl chain of 1 to 4 carbon atoms, and a phenyl group. The linear polydiorganosiloxanes can be waxes, liquids, or gums having viscosities ranging from 5 to 40,000,000 mPa·s at 25° C., and molecular weights of about 300 to 1,000,000. While x can be any value from 0 to approximately 15,000, a preferred range is from 0 to 1000, where x is most preferably 0 to 100.
If the polydiorganosiloxane is cyclic, it can have the formula (SiR
1
R
2
O)
y
, where R
1
and R
2
are as described above, and y is from 3 to 12. Preferably y is from 3 to 8. Most preferably, R
1
is methyl, and R
2
is either alkenyl or methyl.
Component (b) is an amino-functional silane hydrolyzate which may be formed by the reaction of water with alkoxysilanes containing an amine functional group, as in the example shown below.
In the above formula, the value of n is not critical, but a preferred range is approximately 1 to 15,000. Preferably n is selected so that the amino-functional silane hydrolyzate is a liquid with a viscosity in the range of about 1000 to 1,000,000 mpa·s at 25° C. An amine functional group is connected to at least one silicone atom of the amino-functional silane hydrolyzate through a silicon-carbon bond and has the general formula:
R
3
2
—N—(R
4
R
3
—N)
k
—R
5
—
In the above formula, each R
3
is a monovalent group independently selected from the group consisting of hydrogen; alkyl having 1 to 18 carbon atoms, such as methyl, ethyl, propyl, isobutyl, hexyl, octyl, decyl, dodecyl and octadecyl; substituted alkyl having 1 to 18 carbon atoms, such as 3-chloropropyl and 3,3,3-trifluoropropyl; aryl having 6 to 16 carbon atoms, such as phenyl and naphthyl; substituted aryl
DeGroot, Jr. Jon Vierling
Skinner Michael Ward
Warren Stephen Clay
Dow Corning Corporation
Moore Margaret G.
Warren Jennifer S.
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