Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Reexamination Certificate
1994-04-14
2001-05-08
Johnson, Jerry D. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
C526S079000, C526S329200
Reexamination Certificate
active
06228819
ABSTRACT:
The present invention relates to viscosity index improving additives for lubricating oils and, more particularly, to a method for making a copolymer of alkyl (meth)acrylate monomers and a vinyl aromatic monomer.
Lubricating oil compositions for internal combustion engines typically include polymeric additives for improving the viscosity index of the lubricating composition, that is, modifying the relationship between temperature and the viscosity of the oil composition to reduce the temperature dependence of the viscosity and to lower the “pour point” of the composition, that is, to allow the composition to remain fluid at reduced temperature.
Japanese Patent 84020715 (JP '715) discloses an oil soluble copolymer obtained by reaction of 40 weight percent (wt %) to 75 wt % (meth) acrylate monomers composed of 0 parts by weight (pbw) to 80 pbw of a (meth)acrylate having a (C
8
-C
15
)alkyl group and 20 pbw to 100 pbw of a (meth)acrylate having a (C
16
-C
28
)alkyl group; and 25 wt % to 60 wt % of styrene or an alkyl styrene.
While the properties of the copolymer disclosed in JP '715 are desirable, current environmental and health concerns dictate that the amount of residual styrenic monomer present in any commercial embodiment of the copolymer be reduced to a level below 1000 parts per million. JP '715 is silent with respect to the amount of residual styrene monomer present in the copolymers disclosed in that patent.
It is impractical to rely upon running the polymerization reaction to a sufficiently high monomer conversion so as to leave less than 1000 parts per million (ppm) nonreacted styrenic monomer in the copolymeric product, so that relatively costly processing steps as, e.g., stripping of the copolymeric product, may be required to remove residual styrenic monomer from the product copolymer.
A method for making a viscosity index improving copolymer of a (meth)acrylate monomer and a styrenic monomer that overcomes the above-noted difficulties is disclosed hererin. The method includes:
polymerizing a monomer mixture in an oil soluble diluent and in the presence of a polymerization initiator to form a polymerization intermediate, said monomer mixture comprising:
from about 5 parts by weight (pbw) to about 70 pbw of a first (meth)acrylate monomer having the structural formula (1):
wherein:
each R
1
is independently H or CH
3
; and
each R
2
is independently selected from (C
16
-C
24
)alkyl;
from about 5 pbw to about 85 pbw of a second (meth)acrylate monomer having the structural formula (2):
wherein:
each R
3
is independently H or CH
3
; and
each R
4
is independently selected from (C
7
-C
15
)alkyl; and
from about 5 pbw to about 50 pbw of a styrenic monomer; and
polymerizing from about 2 pbw to about 20 pbw additional (meth)acrylate monomer per 100 pbw of the combined first and second (meth)acrylate monomers of the monomer mixture, said additional (meth)acrylate monomer comprising a first (meth)acrylate monomer, a second (meth)acrylate monomer or a mixture thereof, in the presence of the polymerization intermediate, provided that the combined monomers of the monomer mixture and additional monomer comprise from about 5 wt % to about 70 wt % of the first (meth)acrylate monomer, from about 5 wt % to about 85 wt % of the second (meth)acrylate monomer and from about 5 wt % to about 50 wt % of the styrenic monomer, to provide a solution of from about 30 weight percent to about 90 weight percent of a viscosity index improving copolymer in the diluent, said solution including less than or equal to 1000 pbw residual styrene monomer per 1,000,000 pbw solution.
The limitation on the amount of residual styrenic monomer in the product solution may, alternatively, be expressed on the basis of copolymer solids as less than or equal to 3,333 pbw residual styrene monomer per 1,000,000 pbw copolymer solids. In a preferred embodiment, the method of the present invention provides a copolymer solution that includes less than or equal to 1,000 pbw, more preferably, less than or equal 500 pbw, residual styrene monomer per 1,000,000 pbw copolymer solids.
The terminology “(meth)acrylate” is used herein to generally refer to acrylate esters, methacrylate esters and mixtures thereof Commercially available alkyl (meth)acrylate monomers may be, and typically are, mixtures of esters. Such mixtures are typically referred to, and are referred to herein, using a contracted version of the names of the ester species predominating in the mixture, e.g., “lauryl-myristyl methacrylate”, “cetyl-eicosyl methacrylate”, “cetyl-stearyl methacrylate”, “dodecyl-pentadecyl methacrylate”.
As used herein, (C
16
-C
24
)alkyl means any straight or branched alkyl group having 16 to 24 carbon atoms per group, e.g., stearyl, cetyl, heptadecyl, nonadecyl, eicosyl.
Monomers having the structural formula (1) include, for example, stearyl acrylate, stearyl methacrylate, cetyl methacrylate, heptadecyl acrylate, heptadecyl methacrylate, nonadecyl methacrylate, eicosyl methacrylate and mixtures thereof, e.g., cetyl-stearyl methacrylate, cetyl-eicosyl methacrylate.
As used herein, (C
7
-C
15
)alkyl means any straight or branched alkyl group having 7 to 15 carbon atoms per group, e.g., heptyl, octyl, nonyl, n-decyl, isodecyl undecyl, lauryl, tridecyl and myristyl.
Monomers having the structural formula (2) include, for example, octyl acrylate octyl methacrylate, nonyl methacrylate, decyl acrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, myristyl methacrylate, pentadecyl methacrylate and mixtures thereof, e.g., lauryl-myristyl methacrylate.
The term “styrenic monomer” means those polymerizable vinyl aromatic compounds having a single aromatic ring per molecule and mixtures thereof and includes, for example, styrene, alkyl-substituted styrenes such as &agr;-methyl styrene, &agr;-ethyl styrene, p-methyl styrene and vinyl xylene, halogenated styrenes such as chlorostyrene, bromostyrene and dichlorostyrene and other vinyl aromatic compounds having a single aromatic ring per molecule and having one or more nonreactive substituents on the aromatic ring. In a preferred embodiment, the styrenic monomer is styrene.
The copolymer of the present invention is made, e.g., by free radical polymerization of selected relative amounts of the above-disclosed monomers in an oil soluble hydrocarbon diluent in the presence of an effective amount of a polymerization initiator.
In a preferred embodiment, the total monomer charge includes from about 20 wt % to about 50 wt %, more preferably, about 25 wt % to about 35 wt %, (meth)acrylate monomer of the structural formula (1), from about 20 wt % to about 50 wt %, more preferably, about 25 wt % to about 40 wt %, (meth)acrylate monomer of the structural formula (2) and form about 20 wt % to about 40 wt %, more preferably, about 25 wt % to about 35 wt %, of the styrenic monomer.
The diluent may be any inert oil soluble organic liquid and is preferably a hydrocarbon lubricating oil which is miscible with or identical to the lubricating oil base oil in which the additive is to be subsequently employed. In a preferred embodiment, the oil soluble diluent is a paraffinic or naphthenic neutral oil.
In a preferred embodiment, the reaction mixture includes from about 15 to about 400 pbw diluent per pbw total monomer charge and, more preferably, from about 50 to about 200 pbw diluent per 100 pbw total monomer charge. As used herein the terminology “total monomer charge” means all monomers charged to the reaction vessel during the process of the present invention, i.e., the combined monomers of the monomer mixture and the additional (meth)acrylate monomer.
Suitable polymerization initiators include those initiators which dissociate upon relatively mild heating, e.g., at temperatures in the range of 70° C. to 140° C., to yield a free radical. The specific reaction temperature to be used in the polymerization reaction is selected in a known way, based on the composition of the initiator used in the reaction. Suitable initiators are known i
Johnson Jerry D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rohm and Haas Company
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