Note: Descriptions are shown in the official language in which they were submitted.
DISPERSANT POLYMETHACRYLATE VISCOSITY INDEX
IMPROVERS
RELA7 lED U.S. APPLICATION DATA
This application is a continuation-in-part of co-pending application Serial
Number 854,924 filed March 20, 1992.
BACKGRS)UND OP THE INVENTION
This invention relates to polymers derived from (a) monomers selected from
the group consisting of (Cl-C24)aLkyl methacrylates and (Cl-C24)aLlcyl acrylates and (b)
a monomer selected from the group consisting of hydroxy(C2-C6)alkyl methacrylates
and hydroxy(C2-C6)alkyl acrylates wherein the number of carbon atoms in the alkyl
groups averages from about 7 to about 12. These polymers are useful as additives to
lubricating oils for providing viscosity index improvement, dispersancy and low
temperature performance properties without adversely affecting fluoropolymer
seals and gaskets. The novel polymers are normally dissolved or dispersed in
refined rnineral lubricating oil for eventual incorporation in a mineral or synthetic
base oil.
Desirable lubricating oils for internal combustion engines, automatic
transmission fluids and hydraulic fluids have relatively little change in viscosity
over a wide range of temperatures, dispersant properties and good fluidity at low
temperatures, including low pour point. Viscosity index (or VI) is a measure of the
degree of viscosity change as a function of temperature; high viscosity index values
indicate a smaller change in viscosity with temperature variation compared to low
viscosity index values. Viscosity index improver additives having high viscosityindex values coupled with good low temperature fluidit,v allow the oil to flow at the
lowest possible temperature of operation, usually at engine start-up, and, as the
temperature increases into the operating range, the viscosity remains at a levelsuitable for good performance.
Polymeric additives have been used to improve the performance of engine
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lubricating oils in regard to several of these properties. Polymers of alkyl acrylates or
alkyl methacrylates have been used successfully as viscosity index improvers andpour point depressants. Enhanced dispersant properties may be introduced into the
polymer compositions by using polar, particularly basic comonomers, such as vinyl
heterocycles (N-vinylpyrrolidone, N-vinylimiclazole, vinylpyridine and the like),
dialkylaminoalkyl methacrylates, N,N-dialkylaminoalkyl methacrylamides and the
like. However, grafting conditions needed to incorporate the nitrogen-containingbasic comonomers very often introduce poor shear stabllity characteristics. In
addition, viscosity index improvers containing nitrogen-containing basic
comonomers may cause objectionable odor or degrade the effectiveness of gaskets
and seals found in automobile engines that are based on fluoropolymers, such as
VitonTM fluoroelastomer.
U.S. 3,311,597 discloses an approach to improved viscosity index and
dispersant properties of poly(methacrylate) polymers which involves the
copolymerization of alkyl methacrylates with tetrahydrofurfuryl methacrylate andthe optional incorporation of hydroxyethyl methacrylate, hydroxypropyl meth-
acrylate, N-vinyl pyrrolidone or t-butylaminoethyl methacrylate. Poly(alkylmeth-acrylate) polymers having improved pour point properties based on copolymerizingalkyl methacrylates with from 9 to 23 mole percent methacrylic acid followed by
ethoxylation, wherein the average number of carbon atoms in the alkyl group is 12.5
to 14.3, are disclosed in U.S. 3,598,737. A lauryl methacrylate-stearyl methacrylate
copolymer with 23 mole percent hydroxyethyl methacrylate is disclosed in U.S.
3,249,545 for use in oil formulations containing bisphenol antioxidants.
In another approach to providing dispersant viscosity index improvers, EP
418610A disdoses the use of polyalkyl(meth)acrylates characterized in that 80-95.5%
by weight of the copolyIner is derived from (C6-C24)alkyl(meth)acrylates and 0.5-20%
is derived from a hydroxy(C2-C6)alkyl(meth)acrylate or a multialkoxylized alkyl-(meth)acrylate with an optional 0-17% by weight being derived from (C1-Cs)alkyl~(meth)acrylates.
Poly(methacrylate~ polymers as additives for machine tool working oils based
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on 92-99% (C1-Cl8)alkyl methacrylate and 1-8% hydroxy(C2-C3)alkyl methacrylate
pol,vmers having number-average molecular weights (Mn) of 20,000-60,000 are
disclosed in Japanese Patent JP 52-018202B. These polymeric additives are disclosed
as being unsuitable for use as dispersant viscosity index improver additives forengine oils.
None of these latter approaches combines dispersancy, good viscosity index
and compatibility with fluoropolymer sealing materials with good low-temperaturefluidity in a single polymer and it is an object of the present invenlion to provide
this combination of properties in a single poly~ner.
SUMMARY OF THE INVENTION
This invention relates to polymers derived from polyrnerizing monomers
comprising (a) from about 90 to about 98 weight percent of a monomer selected from
the group consisting of (C1-C24)alkyl methacrylates and (C1-C24)alkyl acrylates and (b)
from less than 10 to about 2 weight percent of a monomer selected from the groupconsisting of hydroxy(C2-C6)alkyl methacrylates and hydroxy(C2-C6)aLl~yl acrylates
wherein the number of carbon atoms in the side chain alkyl groups of the backbone
polymer averages from about 7 to about 12. These polymers are llseful as additives
to lubricating oils for providing viscosity index improvement, dispersancy and low
temperature performance properties without adversely affecting fluoropolymer
seals and gaskets. The novel polymers, when used in lubricating oils, are normally
dissolved or dispersed in refined mineral lubricating oil for eventual incorporation
in a mineral or synthetic base oil. Examples of lubricating oils include crankcase
engine oils, automatic transmission fluids, hydraulic fluids, gear oils and shock
absorber fluids.
DETAILED DESCRIPTION OF THE INVEN~ION
Each of the monomers used in the present invention can be a single
monomer or a mixture having different nurnbers of carbon atoms in the alkyl
portion. The alkyl portion of both the (a) methacrylate and acrylate monomers and
the (b) hydroxyalkyl methacrylate and acrylate monomers is an important factor ir
the performance characteristics of the polymers of the inve.ntion. By this is meant
that the average number (n) of carbon atoms (Cn) in the side chain alkyl and hydroxy-
alkyl groups of the acrylate or methacrylate backbone ~olymer is selected to
maximize viscosity index characteristics and to maintain oil solubility of the
pol,vmer additive in both new oil and in used oil, where the additive has functioned
as a sludge dispersant. Generally, when the average Cn is less than about 7, theresultant polymers may have poor solubility in the base oils and the additives may
not be fully functional as dispersant viscosity index improvers. When the average
Cn is significantly greater than about 12, poorer low temperature fluidity properties
may be observed. By low temperature is meant temperatures below about -5C::.
Consequently, the average number of carbon atoms in the alkyl group of the acrylate
or methacrylate monomers used to prepare the polymeric additives is from about 7to about 12, preferably from about 8 to about 10. In the instance where the
monomers are all acrylates or substantially all acrylates, then the average carbon
number of the side chain alkyl groups of the backbone polymer will vary somewhatand the average number of carbon atoms will be that which matches the solubilityparameters of the corresponding methacrylate backbone polymers. Such solubility
parameters are readily known and understood by those in the art.
Preferably, monomer (a) is selected from the group consisting of (C1-C20)alk
methacrylates and (Cl-C20)alkyl acrylates and monomer (b) is selected from the
group consisting of hydroxy(C2-C6)alkyl methacrylates and hydroxy(C2-C6)alkyl
acrylates. The allcyl portion of either monomer may be linear or branched. Alkylmethacrylates and hydroxyaLIcyl methacrylates are preferred.
To obtain a balance of desired performance characterisistics relating to
viscosity index improvement, good dispersancy and low temperature performance,
rnixtures of aLkyl methacrylates and alkyl acrylates are used. Consequently, in one
embodiment of the invention, monomer (a) generally comprises (i) O to about 40%
of an alkyl methacrylate or alkyl acrylate in which the alkyl group contains from 1 to
6 carbon atoms, and mixtures thereof, (ii) frorn about 30 to about 90% of an alkyl
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methacrylate or alkyl acrylate in which the alkyl group contains from 7 to 15 carbonatoms, and mixtures thereof, and (iii) 0 to about 40% of an alkyl methacrylate or
alkyl acrylate in which the alkyl group contains from 16 to 24 carbon atoms, andmixtures thereof, and monomer (b) comprises from less than 10 to about 2% of a
hydroxyalkyl methacrylate or hydroxyaL~yl acrylate in which the alkyl group
contains 2 to 6 carbon atoms and is substituted with one or more hydroxyl groups.
All percentages are by weight, are based on the total weight of the polymer and the
total of (i), (ii), (iii) and (b) equals 100 percent of the weight of the polymer. The
amount of (i) in the polymer is preferably from ~ to about 25%; the amount of (ii) is
preferably from about 45 to about 85% and more preferably from about 50 to about60%; the amount of (iii) is from about 5 to about 35% and more preferably from
about 25 to about 35%; and the amount of (b) is preferably from about 4 to about 8%
and more preferably about 5 to about 6%.
Examples of monomer (a), the alkyl methacrylate or alkyl acrylate where the
alkyl group contains from 1 to 6 carbon atoms, also called the "low-cut" alkyl
methacrylate or alkyl acrylate, are methyl methacrylate (MMA), methyl and ethyl
acrylate, propyl methacrylate, butyl methacrylate (BMA) and acrylate (BA), isobutyl
methacrylate (IBMA), hexyl and cyclohexyl methacrylate, cyclohexyl acrylate and
combinations thereof. Preferred low-cut alkyl methacrylates are methyl
methacrylate and butyl methacrylate.
Examples of monomer (a~, the alkyl methacrylate or alkyl acrylate where the
alkyl group contains from 7 to 15 carbon atoms, also called the "mid-cut" aLkyl
methacrylates or alkyl acrylates, are 2-ethylhexyl acrylate (EHA), 2-ethylhexyl
methacrylate, octyl methacrylate, decyl methacrylate, isodecyl methacrylate (ID~A,
based on branched ~CIo)alkyl isomer mixture), undecyl methacrylate, dodecyl
methacrylate (also known as lauryl methacrylate), tridecyl methacrylate, tetradecyl
methacrylate (also known as myristyl methacrylate), pentadecyl methacrylate and
combinations thereof. Also useful are: dodecyl-pentadecyl methacrylate (DPMA), amixture of linear and branched isomers of dodecyl, tridecyl, tetradecyl and penta-
decyl methacrylates; and lauryl-myristyl methacrylate (LMA), a mixture of dodecyl
IJ~J~
and tetradecyl methacrylates. The preferred mid-cut alkyl methacrylates are lauryl-
myristyl methacrylate and isodecyl methacrylate.
Examples of monomer (a), the alkyl methacrylate or alkyl acrylate where the
aLkyl group contains from 16 to 24 carbon atoms, also called the "high-cut" alkyl
methacrylates or alkyl acrylates, are hexadecyl rnethacrylate, heptadecyl meth-
acrylate, octadecyl methacrylate, nonadecyl met'hacrylate, cosyl methacrylate, eicosyl
methacrylate and combinations thereof. Also useful are: cetyl-eicosyl methacrylate
(CEMA), a mixhlre of hexadecyl, octadecyl, cosyl and eicosyl methacrylate; and cetyl-
stearyl methacrylate (SMA), a rnixture of hexadecyl and octadecyl methacrylate. The
preferred high-cut alkyl methacrylates are cetyl-eicosyl methacrylate and cetyl-stearyl
methacrylate.
The mid-cut and high-cut alkyl methacrylate and alkyl acrylate monomers
described above are generally prepared by standard esterification procedures using
technical grades of long chain aliphatic alcohols, and these commercially available
alcohols are mixtures of alcohols of varying chain lengths containing between 10and 15 or 16 and 20 carbon atoms in the alkyl group. Consequently, for the purposes
of this invention, alkyl methacrylate is intended to include not only the individual
alkyl methacrylate product named, but also to include mixhlres of the alkyl meth-
acrylates with a predorninant amount of the particular alkyl methacrylate named.The use of these commercially available alcohols to prepare acrylate and meth-
acrylate esters results in the LMA, DPMA, SMA and CEMA monomer mixtures
described above.
Examples of monomer (b) are those alkyl methacrylate and acrylate
monomers with one or more hydroxyl groups in the aLkyl radical, especially thosewhere the hydroxyl group is found at the ,B-position (2-position) in the alkyl radical.
HydroxyaL~cyl methacrylate and acrylate monomers in which the substituted alkyl
group is a (C2-C6)aLkyl, branched or unbranched, are preferred. Among the hydroxy-
alkyl methacrylate and acrylate monomers suitable for use in the present invention
are 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate, 2-hydroxypropylmethacrylate, l-methyl-2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate,
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l-methyl-2-hydroxyethyl acrylate, 2-hydroxybutyl methacrylate and 2-hydroxybutylacrylate. The preferred hydroxyalkyl methacrylate and acrylate monomers are
HEMA, 1-methyl-2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate.
A mixture of the latter two monomers is commonly referred to as "hydroxypropyl
methacrylate" or HPMA, which is a more preferred hydroxyalkyl methacrylate as are
each of the components of the HPMA.
Among the hydroxyalkyl methacrylate and acrylates monomers of interest,
preferred are those monomers which are essentially free of crosslinker or cross-linker precursor impurities and contaminants which may be present as a result ofthe method of preparation of the monomer. By crosslinker is meant any poly-
functional material which causes crosslinking of the polymer, such- as ethylene
glycol dimethacrylate. The presence of these crosslinker materials detracts fromproperties of the additives of the invention due to gel formation and related
problems. Preferred hydroxyalkyl methacrylate and acrylates are those containingless than about 0.5%, more preferably less than about 0.2% and most preferably about
0.1% or less by weight of crosslinker or crosslinker precursor materials.
Preferred polymers are those where monomer (a) comprises monomers
wherein (i) is selected from one or more of the group consisting of methyl meth-acrylate, butyl methacrylate and isobutyl methacrylate, (ii) is selected from one or
more of the group consisting of 2-ethylhexyl methacrylate, isodecyl methacrylate,
dodecyl-pentadecyl methacrylate and lauryl-myristyl methacrylate, (iii) is selected
from one or more of the group consisting of cetyl-stearyl methacrylate and cetyl-
eicosyl methacrylate, and monomer (b) is selected from one or more of the group
consisting of 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl
methacrylate, 1-methyl-2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate,
1-methyl-2-hydroxyethyl acrylate, 2-hydroxybutyl methacrylate and ?-hydroxybutylacrylate.
A preferred polymer is one in which monomer (a) is about 10% methyl
methacrylate, about 55% isodecyl methacrylate and about 30% cetyl-stearyl or cetyl-
eicosyl methacrylate, and monomer (b) is about 5% of a mixture of 2-hydroxypropyl
.
methacrylate and 1-methyl-2-hydroxyethyl methacrylate.
Another preferred polymer is one in wh;ch monomer (a) is about 20% butyl
or isobutyl methacrylate, about 45% isodecyl methacrylate and about 30% cetyl-
stearyl or cetyl-eicosyl methacrylate, and monomer (b) is about 5% of a mixture of
2-hydroxypropyl methacrylate and 1-methyl-2-hydroxyethyl methacrylate.
Another preferred polymer is one in which monomer (a) is about 15~o butyl
or isobutyl methacrylate and about 80% lauryl-rnyristyl or dodecyl-pentadecyl
methacrylate and monomer (b) is about 5% of a mixture of 2-hydroxypropyl
methacrylate and 1-methyl-2-hydroxyethyl methacrylate.
Another preferred polymer is one in which monomer (a) is about 5 to about
10% methyl methacrylate, about 85 to about gO% lauryl-myristyl, isodecyl or dodecyl-
pentadecyl methacrylate, and 0 to about 5% cetyl-eicosyl methacrylate and (b) isabout 5% of a mix of 2-hydroxypropyl and 1-methyl-2-hydroxyethyl methacrylate.
A polymer composition which is particularly preferred for use in automatic
transmission fluids is one in which monomer (a) is 0 to about 5% methyl meth-
acrylate, about 80 to about 90% lauryl-myristyl methacrylate and 0 to about 10% cetyl-
eicosyl methacrylate, and monomer (b) is about 5% of a mixture of 2-hydroxypropyl
methacrylate and 1-methyl-2-hydroxyethyl methacrylate.
Another preferred polymer composition for use in automatic transrnission
fluids is one in which monomer (a) is 0 to about 20% butyl methacrylate, about 65 to
about 90% lauryl-myristyl methacrylate and 0 to about 10% cetyl-eicosyl meth-
acrylate, and monomer (b) is about 5% of a mixture of 2-hydroxypropyl methacrylate
and 1-methyl-2-hydroxyethyl methacrylate.
Besides the average number (n) of carbon atoms (Cn) in the side chain alkyl
and hydroxyalkyl groups of the acrylate or methacrylate backbone polymer, the
nature of the alkyl portion of the methacrylate and acrylate monomers is an
important factor in the performance characteristics of the polymers of the
invention. For example, a mix of (C1-C6)alkyl methacrylates or acrylates,
(C7-C1s)alkyl methacrylates or acrylates and (C16-C24)aL~cyl methacrylates or acrylates
may be copolymerized with a hydroxyaL~cyl methacrylate such that ~e polymer has
an average carbon number content in the alkyl side chains of about 9. In this case
there is a good balance of viscosity index properties and solubility in base oils; in
addition, the (Cl6-C24)aLkyl methacrylate portion of the polymer is wax-like and will
interact with the waxy components in ~e base oil resulting in improved low-
temperature properties, e.g., pour point, low temperature pumpability and cold-
cranking engine ~tartup. If, on the other hand, a single (Clo) or (Cl2)alkyl meth-
acrylate monomer is copolymerized with a hydroxyalkyl methacrylate to provide anaverage carbon number in the alkyl side chains of about 9, the resulting polymeradditive would have satisfactory oil solubility but little wax interactioll capability
resulting in poorer low-temperature properties, such as poorer pumpability due to
viscosity buildup, even though the Cn values are similar for both types of polymer.
Consequently, to obtain good low temperature performance properties, while
retaining a good balance of viscosity index properties and solubility in base oils, it is
preferred that a portion of monomer (a3 comprise from about 5 to about 40,
preferably from about 5 to about 35 and more preferably from about 25 to about 35
weight percent of (Cl6-C24)alkyl methacrylates and (Cl6-C24)alkyl acrylates, preferably
wherein the alkyl portion is Cl6 to C2n. Low temperature performance refers to
viscosity under high shear and low shear conditions. For example, cold cranking
startup of an engine, as measured by CCS (Cold-Cranking Simulator) viscosity,
relates to viscosity at high shear conditions. On the other hand, pumpability of an
oil at low temperatures, as measured by the mini-rotary viscometer (Ml~V), relates
to viscosity under low shear conditions. Since the high-cut alkyl methacrylate and
acrylates are wax-like, they act as pour point depressants changing the structure or
morphology of the wax in the base oil at low temperatures. The amount of the high-
cut alkyl methacrylate or acrylate used is dependent upon the particular high-cut
alkyl methacrylate or acrylate selected, the properties of the base oil and the desired
low temperature properties. Generally, the greater the number of carbons in the
alkyl portion the more wax-like properties the monomers have and less of this
monomer is used. Since these high-cut alkyl methacrylates are wax-like, too muchcan cause congealing in the base oil and loss of low temperature fluidity.
:`
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- The optirnization of the ratio of the high-, mid- and low-cut alkyl meth-
acrylates is dependent on the base oils used in the formulation and the level ofperformance desired. Once the high-cut monomer is optimized then the mid- and
low-cut monomer ratios are balanced to give ~ptimum viscosity index and
solubility. The balanced formulation will have an alkyl carbon content (Cn) of from
about 8 to about 10.
Thus, within the preferred ranges for the various monomers, including the
hydroxyalkyl methacrylate and acrylate monorners, and the average number of
carbon atoms in the side chain alkyl groups of the backbone polymer, the addition of
a polymer of the present in~ention can result in an engine oil formulation
exhibiting the viscosit,v and low temperature fluidity properties of an oil a full
viscosity grade lo~ver. For example, an SAE 10W-30 oil would meet the pumpability
requirements of an SAE 5W-30 oil.
Within these preferred ranges, the polymers of the present invention also
provide a lower CCS viscosity while maintaining good low temperature
pumpability (measured by MRV) of lubricating oils, thus allowing the use of baseoils having higher viscosities. Consequently, the polymers of the invention allow
more extensive use of these heavier base oils in formulated oils, resulting in lower
costs, reduced oil consumption and also cleaner engines since these heavier base oils
are less volatile than lighter viscosity base oils and reduce piston deposit formation
at high operating temperatures, particularly in diesel engines.
In order to achieve the combination of polymer solubility, viscosity index,
dispersancy and low temperature properties (such as pour point and cold-crankingengine startup performance) of polymers of the present invention, use levels of low-
cut (Cl-C3)alkyl methacrylates, such as methyl methacrylate, may be from zero toabout 25%, typically frorn about 5 to about 15% by weight of the polymer. Polymer
solubility refers to the property in which the more hydrophilic or polar monomers,
such as those having a low carbon content ~Cl-C3) in the alkyl portion, provide a
polymer that is less soluble in the base oils than polymers from the more
hydrophobic monomers, such as those having a high carbon content (C4 or greater)
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in the alkyl chain. Therefore, if greater than about 10% methyl methacrylate isincorporated into some polymers, depending upon the level of other polar
monomers used, e.g., hydroxyalkyl methacrylate, solubility in some base oils may be
insufficient for the additive to be fully functional as a dispersant viscosity index
improver. On the other hand, if low-cut (C4-C6)alkyl methacrylates are used, such as
butyl methacrylate or isobutyl methacrylate, then zero to about 40% by weight,
preferably 2Q to 35%, of these monomers may be used to provide an optimum
balance of the aforementioned properties, including solubility in the base oils.The weight-average molecular weight (Mw) of the present invention's
polymers is not highly critical. It must be sufficient to impart the desired viscosity
properties to the lubricating oil. As the weight-average molecular weights of the
polymers increase, they become more efficient thickeners; however, they can
undergo mechanical degradation in particular applications. Thus, the Mw is
ultimately governed by thickening efficiency, cost and the type of application. In
general, polymeric lubricating oil additives of the present invention have Mw from
about 100,000 to about 1,000,000 (às determined by gel permeation chromatography(GPC), using poly(alkylmethacrylate) standards); preferably, Mw is in the range from
about 300,000 to about 800,000 in order to satisfy the particular use application of the
oil, e.g., engine oil and automatic transrnission fluid. Weight-average molecular
weights of from about 100,000 up to about 300,000 are preferred for hydraulic fluids,
gear oils and the like.
Those skilled in the art will recognize that the molecular weights set forth
throughout this specification are relative to the methods by which they are
determined. For example, molecular weights determined by gel permeation
chromatography (GPC) and molecular weights calculated by other methods, may
have different values. It is not molecular weight per se but the handling
characteristics and performance of a polymeric additive (shear stability and
thickening power under use conditions) that is important. Generally, shear stability
is inversely proportional to molecular weight and use of a very shear stable additive
will require more polymer to obtain good thickening.
- -
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The shear stability index (SSI) can be directly correlated to polymer molecular
weight and is a measure of the percent loss in polymeric additive-contributed
viscosity due to shear and can be deteDned by measuring sonic shear stability
according to ASTM D-2603-91 ~published by thle American Society for Testing and
Materials). In general, higher molecular weight polymers undergo the greatest
relative reduction in molecular weight when subjected to high shear conditions
and, therefore, these higher molecular weight polymers also exhibit the largest SSI
values. The SSI range for the polymers of this invention is from about 10 to about
75%, preferably from about 10 to about 25% for low molecular weight polymers andfrom about 30 to about 50% for high molecular weight polymers. The desired SSI
can be achieved by either var,ving the reaction conditions or by mechanically
shearing the known molecular weight product polymer.
Representative of the types of shear stability that are observed for lubricatingoil additives of different weight-average molecular weights (Mw~ are the following:
conventional poly(methacrylate) additives having Mw of 130,000, 490,000 and
880,000, respectively, would have SSI values (210F) of 0, 5 and 20%, respectively,
based on a 2000 mile road shear test for engine oil formulations; based on a 20,000
mile high speed road test for automatic transmission fluid (ATF) formulations, the
SSI values (210F) were 0, 35 and 50%, respectively; and based on a 100 hour ASTM
D-2882-90 pump test for hydraulic fluids, the SSI values (100F) were 18, 68, and 76%,
respectively (Effect of Viscosity Index Improver on In-Service Viscosity of Hydraulic
Fluids, R.J. Kopko and R.L. Stambaugh, Fuel and Lubricants Meeting, Houston,
Texas, June 3-5, 1975, Society of Automotive Engineers).
The polydispersity index of the oil-soluble polymers of the present invention
may be from 1.5 to about 15, preferably from 2 to about 4. The polydispersity index
~W/Mn) is a measure of the narrowness of the molecular weight distribution with a
minimum value of 1.5 and 2.0 for polymers involving chain termination via
combination and disproportionation, respectively, and higher values representingincreasingly broader distributions. It is preferred that the molecular weight
12
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distribution be as narrow as possible, but this is generally limited by the method of
manufacture. Some approaches to providing narrow molecular weight
distributions (low MW/Mn) may include one or more of the following methods:
anionic polymerization, continuous-feed-stirred-tank-reactor (CFSTR) technology,low-conversion polymeri~ation, control of temperature, etc., during
polymerization, mechanical shearing, e.g., homogenization, of the polymer and the
like.
Polymers of the present invention having a polydispersity index from 2 to
about 4 are preferred because these polymers allow more efficient use of the additive
to satisfy a particular formulated engine oil viscosity specification, e.g., about 5 to
10% less additive may be required to produce a viscosity of about 9 to about 20
centipoise (at 100C) in a 100N base oil compared to an additive having a
polydispersity index of about 10.
Thus, a fully effective poly~ler additive should provide a balance of shear
stability and thickening ability at low usage levels, impart low temperature fluidity
without detracting from other properties, such as dispersancy, and be chemicallyneutral to fluoropolymer seals and gaskets. Typically, these performance properties
in engine oils, automatic transrnission fluid formulations and the like, were only
achieved by mixing two, three or more different additives, i.e., using separate
dispersant, viscosity index improver, and pour point depressant additives. The
additives of the present invention provide this combination of performance
properties in a single polymer.
The polymers of this invention are prepared by mixing monomers (a) and (b)
- in the presence of a polymerization initiator, a diluent and optionally a chain
transfer agent. The reaction can be run under agitation in an inert atmosphere at a
temperature of from about 60 to 140C and more preferably from 115 to 125C.
Typically, the batch will exotherm to the polymerization temperature of 115-120C.
The reaction is run generally for about 4 to 10 hours or until ~e desired degree of
polymerization has been reached. As is recognized by those skilled in the art, the
time and temperature of the reaction are dependent on the choice of initiator and
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can be varied accordingly.
Initiators useful for this polymerizalion are any c)f the well known free-
radical-producing compounds such as peroxy, hydroperoxy and azo initiators
including acetyl peroxide, benzoyl peroxide, lauroyl peroxide, t-butyl peroxyiso-
butyrate, caproyl peroxide, cumene hydroperoxide, 1,1-di(f-butylperoxy)-3,3,5-tri-
methylcyclohexane, azobisisobutyronitrile and t-butyl peroctoate. The initiator
concentration is normally between 0.025 and 1% by weight based on the total weight
of the monomers and more preferably from 0.05 to 0.25%. ~hain transfer agents
may also be added to the polymerization reaction to control the molecular weight of
the polymer. The preferred chain transfer agents are alkyl mercaptans such as lauryl
(dodecyl) mercaptan, and the concentration of chain transfer agent used is from O to
about 0.5% by weight.
Among the diluents suitable for the polymerization are aromatic
hydrocarbons, such as benzene, toluene, xylene, and aromatic naphthas, chlorinated
hydrocarbons such as ethylene dichloride, esters such as ethyl propionate or butyl
acetate, and also petroleum oils or synthetic lubricants.
After the polymerization, tXe resultant polymer solution has a polymer
content of between about 50 to 95% by weight. The polymer can be isolated and used
directly in mineral or synthetic base oils or the polymer and diluent solution can be
used in a concentrate form. When used in the concentrate form the polymer
concentration can be adjusted to any desirable level with additional diluent
(paraffinic base oil). The preferred concentration of polymer in the concentrate is
from 30 to 70% by weight. When the concentrate is directly blended into a
lubricating base oil, the more preferred diluent is any mineral oil, such as 10û to 150
neutral oil (lOON or 150N oil), which is compatible with the final lubricating base
oil.
When a polymer of the present invention is added to lubricating base oils,
such as automatic transrr~ission fluids, hydraulic fluids and engine oils, whether it is
added as pure polymer or as concentrate, the final concentration of the polymer in
the lubricating base oil is from about 0.5 to 15% by weight and more preferably from
14
about 1 to 8%, depending on the specific use application requirements. For example,
about 1.5 to about 5% in engine oils, automatic transmission and shock absorber
fluids, and up to as much as 10 to 15% in special application gear oils and hydraulic
fluids. Lubricating base oils may be either mineral oil types (paraffinic or
naphthenic) or synthetic types (polyolefin). The concentration used is dependent on
the desired viscometric properties of the lubricating oil and the severity of shear in
the intended application; generally, if a low molecular weight polymer is used, a
higher concentration is necessary to achieve adequate thickening in the blend and if
a high molecular weight polymer is used, a lower concentration can be used in the
oil.
The polymers of the present invention were evaluated by a wide variety of
performance tests commonly used for lubricating oils and they are discussed below.
Engine oils containing viscosity index improvers generally have viscosity
index (VI) values in the range of 120 to about 230, values greater than about 140
being preferred depending upon the blend specifications. The higher the value, the
less the change in viscosity as the temperature is raised or lowered. Viscosity index
improver compositions of the presen~ invention offer high viscosity index .values
(Example 4) while maintaining good dispersancy (Example 5), good cold-cranking
engine startup (Example 7) and good chemical neutrality towards fluoropolymer
seal materials (Example 6).
Performance characteristics of lubricating oil additives of the present
invention were also evaluated for engine cleanliness in the Sequence VE Test,
which measures the sludge dispersant characteristics of additives under low and
medium temperature operating conditions according to the conditions described inASTM Research Report No. D-2:1002. The engine parts were evaluated and rated at
the end of 12 days and cleanliness was rated according to a Coordinating Research
Council (CRC) merit system with a value of 10 representing the cleanest engine;
target values for average sludge and for rocker arm cover (RAC~ sludge are greater
than 9.00 and 7.00, respectively.
Compositions of the present invention were also subjected to a compatibility
- :
2?~
test for fluorohydrocarbon polymers, in particular, vitonTM fluoroelastomers. This
test (Engine Seal Compatibility Test, Example 6) was used to evaluate the degree of
compatibility of the lubricating oil additives of the present invention with materials
used in engine seals, gaskets, etc. The test is based on the immersion of seal or
gasket materials in fluids containing candidate lubricating oil additive samples for 7
days, after which their elongation characteristics (percent elongation-at-break or
%ELB) were determined. Values of the relative change in %ELB of zero to -5% wererepresentative of neutral conditions, i.e., compatibile with the engine seals.
Compositions of the present invention were subjected to tests designed to
measure viscosity performance at low temperatures at low and high shear rates, i.e.,
according to the SAE J30Q Engine Oil Viscosity Classification, January, 1991. In these
circumstances the viscosity of the formulated oil should be low enough to allow
sufficient crarlking speed for startup of the engine while providing adequate
lubrication of all engine parts.
The Cold-Cranking Simulator (CCS) test estimates the apparent viscosity of
engine oils under conditions where engine cranking and startup is mast dif~icultand is based on the procedure defined in ASTM D-5293-92. For example, the CCS
viscosity specification for an SAE 5W-30 grade oil is less than 35 poise at -25C and it
is difficult to satisfy this requirement with many of the commercially availableviscosity index improvers.
The mini-rotary viscometer (MRV) test procedure measures low-temperature
low-shear performance at engine startup. The MRV test (Example 8) is a measure of
the pumpability of an engine oil, i.e., the engine oil must be fluid enough so that it
can be pumped to all engine parts after engine startup to provide adequate
lubrication. Dispersant viscosity index improvers of the present invention offergood low-temperature performance when forrnulated in a wide range of different
base oils.
The following examples are intended to illustrate the inven~on and not to
lirnit it, except as it is limited in the claims. All ratios and percentages are by weight,
and all reagents are of good commercial quality unless otherwise indicated.
16
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2~ ;5
Examples 1 through 3 give synthesis information for preparing polymers of the
present invention and Examples 4 through 7 give performance data on oil
formulations containing polymers of the invention.
EXAMPLE 1
A monomer mix was prepared from 30.0 parts cetyl-eicosyl methacrylate
(100% basis, 95% purity), 55.0 parts isodecyl methacrylate (100% basis, 98% purity),
10.0 parts methyl methacrylate, 5.0 parts hydroxypropyl methacrylate, 0.06 partsdodecyl mercaptan, and 0.10 parts 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane.
A heel charge was prepared from 20.0 parts paraffin~c oil base stock (lOON oil) and
0.028 parts 1,1-di(f-butylperoxy)-3,3,~trimethylcyclohexane. The heel charge wasthen charged to a nitrogen flushed kettle fitted with a thermometer and
ThermowatchTM to control temperature, a water-cooled reflux condenser with
nitrogen outlet, a stirrer, a nitrogen inlet, and an addition furmel to control the
addition of the monomer mK. The contents of the flask were heated to 120C and
held there. The monomer mix (100 parts) was then added uniformly over a 90
minute period and heating or cooling was applied as needed to maintain the
polymerization temperature at 115-120C.
Twenty minutes after the end of the monomer feed, the first of three delayed
initiator shots, each containing 0.10 parts of 1,1-di(t-butyl-peroxy)-3,3,5-trimethyl-
cydohexane in 10.0 parts paraffinic base oil, were added. The other two initiator
shots were added at twenty minute intervals. Twenty minutes after the last initiator
addition, about 62 parts of paraffinic base oil was added to bring the batch to a
theoretical solids of 50% polymer in oil. Throughout the polymerization, the batch
temperature was maintained at 115-120C. Thirty mimltes after the addition of the
paraffinic base oil, the batch was homogeneous and the polymerization was
considered complete. The conversion of monomer to polymer was about 95% and
the polymer had a shear stability index (SSI) of 45 (according to ASTM D-2603-91).
lEXAMPLE 2
The same procedure as Example 1 was followed except the monomer rnix uras
145 parts cetyl-eicosyl methacrylate, 225 parts isodecyl methacrylate, 99 parts butyl
methacrylate, 24 parts hydroxypropyl methacrylate and 0.19 parts cumene
hydroperoxide. The heel charge was 106 parts paraffinic base oil containing 0.1 gram
cumene hydroperoxide and 0.83 parts of 25% tallow-t-octylphenyldimethyl-
ammonium chloride in mixed butanols. Also, the three delayed initiator shots
were added at 30 minute intervals and each consisted of 0.13 parts of cumene
hydroperoxide and 0.83 parts of 25% tallow-t-octylphenyldimethylammonium
chloride in mixed butanols in 3.6 parts paraffinic base oil. The batch had a
theoretical solids of 52% polymer. The conversion of monomer to polymer was
about 93% and the polymer had an SSI of 73.3.
EXAMPLE 3
A monomer mix was prepared from 5.0 parts cetyl-eicosyl rnethacrylàte (100%
basis, 95% purity), 85.0 parts isodecyl methacrylate (100% basis, 95% purity), 5.0 parts
methyl methacrylate, 5.0 parts hydroxypropyl methacrylate, 0.29 parts dodecyl
mercaptan, 0.13 parts t-butyl peroctoate (t-butyl peroxy-2-ethylhexanoate) and 4.9
parts paraffinic base oil (lOON oil). Part of the above monomer mix (40%) was
charged to a nitrogen flushed kettle fitted with a thermometer and ThermowatchTMto control temperature, a water-cooled reflux condenser with nitrogen outlet, a
stirrer, an nitrogen inlet, and an addition funnel to control the addition of the
monomer mix. The contents of the kettle were heated to 105C and allowed to
exotherm to 130C before controllirlg by cooling to maintain the temperature below
130C; if the exotherm had not started after about 5 minutes at 105C, the batch was
heated slowly to 115-120C until the exotherrn started. When the temperature
reached 115C during the exotherm the rernainder of the monomer mix was then
added uniformly over a 45 min~te period with cooling to control the exotherm
below 125C. The temperature was then maintained at 115-120C for an additional
18
30 minutes. At this point the first of three delayed initiator shots, each consisting of
0.10 parts t-butyl peroctoate in 9.8 par~s 100N oil, was added to the kettle after which
the batch was held at the same temperahlre for 30 minutes. Two additional initiator
shots were made at thirty minute intervals. Thirty minutes after the last ad~ition of
initiator, approximately 65 parts of 100N base oil was added to dilute the batch to
about 50% polymer. The batch temperature was then raised to 130~C and held therefor 30 mi~utes. The final diluted polymer solution had an SSI of 13.2.
EXAMPLE 4
Viscosity index (VI) is a measure of the effect of temperature change on the
kinematic viscosity of an oil. Viscosity index is expressed as an arbitrary value based
on a calculation according to ASTM method D-2270-74 from kinematic viscosity
(centistokes) measured at 40C and 100C. Table 1 contains data on viscosity index
improvers which have been formulated in two different base oils. Viscosity indeximprover (VII) compositions 1-2 represent poly(alkylmethacrylate) additives of the
prior art which contain no hydroxyalkyl methacrylate monomer; VII compositions
3-7 are representative of the present invention based on poly(MMA/IDMA/CIiMA/
HPMA) with relative monomer contents of 9-10/53-56/28-30/4-6 parts by weight,
respectively.
TABLE 1
Viscosity Index Val~es
Formulation 1 Formulation 2
VI I %HPMA 100 40 VI 100 40 VI
0 11.0 57.1 189 10.6 54.9 187
2 0 10.6 55.8 186 10.3 53.6 185
3 4 10.6 53.5 195 10.2 50.5 197
4 4 10.9 54.4 197 10.5 51.5 201
10.4 52.3 195 10.1 49.5 197
6 5 10.7 50.7 211 10.5 51.0 203
7 6 9.8 42.9 192 9.5 46.0 199
19
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EXAMPLE 5
Performance characteristics in the Sequence VE Test (engine cleanliness) of
the lubricating oil additives of the present invention are presented in Table 3. The
sludge values listed in Table 2 are for the rocker arm cover sludge and the average
sludge (target values are greater than 7.0 and 9.0, respectively, with 10.0 representing
the cleanest engine). Each of the formulations, M through S, contains 4-8% of the
oil additive being tested, 8-10% of a commercial DI package, and 82-87% of a
paraffinic base oil. Commercial DI packages typically consisted of an antiwear or
antioxidant component, such as zinc dialkyl dithiophosphate; an ashless dispersant,
such as polyisobutene based succinimide; a detergent, such as metal phenate or
sulfonate; a friction modifier, such as sulfur-containing organic; and an antifoam
agent such as silicone fluid: HitecTM 993 is available from Ethyl Corporation and
Amoco~9 A-8004 is available from Amoco Chemicals. The oil additives tested were
based on poly(MMA/IDMA/CEMA/HPMA) with relative monomer contents of
9-10/53-56/28-30/4-8 parts by weight, respectively. The paraffinic base oils used were
Exxon 100N or 150N oils.
The compositions of the various formulations tested were:
M 4.7% additive/8% HitecTM 993 DI package/87% 150N oil
N 4.5% additve/8% HitecTM 993 DI package/87% 150N oil
0 6.9% additive/10% Amoco~3' A-8004 DI package/83% 100N oil
P 6.7% additive/10% Amoco~ A-8004 DI package/83% 100N oil
Q 7.7% additive/10% Amoco~9 A-8004 DI package/82% 100N oil
R 6.5% additive/10% Amoco~ A-8004 DI package/83% 100N oil
S 4.4% additive/10% Amoco~ A-8004`DI package/78% 100N oil/
7% 150N oil
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TABLE 2
Sequence VE Test (Engine Cleanliness~
% ~PMA in Sludge
Formulation Additive (Rocker Arm Cov/Aver)
M 5% 9.3/9.4
N 5% 9.3/9.1
O 5% 9.4/9.4
P 5% 9.2/9.4
Q 5% 9.3/9.6
R 4% 8.1/8.0
S 8% 9.4/9.5
EXAMPLE 6
Compositions of the present invention were subjected to a compatibility test
(Engine Seal Compatibility Test) for fluorohydrocarbon polymers, in particular,
VitonTM fluoroelastomers, used in engine seals, gaskets, etc. This test was conducted
under conditions sirnilar to those defined in the ISO-37-1977(E) prvcedure
(developed by the technical committee of the International Organization for
Standardization (ISO/TC45)) using a S3A dumb-bell shaped test specimen.
Evaluation was conducted as follows: in a beaker, three S3A dumb-bell
shaped specirnens made of VitonTM fluoroelastomer (AK6) were immersed in the
test fluid such that 80 parts of test fluid were present per 1 part of test specimen
(volume/volume). The test fluid contained 5% (weight) of the dispersant viscosity
index improver composition to be tested together with an appropriate detergent-
inhibitor (DI) package at a recommended use level in Exxon 150N oil. The beaker
was then covered with a watch glass and placed in a forced-air oven maintained at
149-151C. The test specimens were subjected to the above conditions for 7 days,after which they were removed, allowed to cool and then rinsed lightly with hexane
to remove residual test fluid. The test specimens were then air-dried and the tensile
strength and elongation characteristics (percent elongation-at-break OI %ELB) were
determined using a standard stress-strain measurement procedure at 5.75
21
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inches/minute elongation rate. The change of elongation of VitonTM elastomer test
specimens was then compared to the elongation data from untreated VitonTM
elastomer samples and the result was expressed as a percentage:
[%ELBtreated - %ELBuntreated] X 100 = %ELB Change
[%ELBuntrec~ted]
The more negative the value for %ELB Change, the greater the aggressiveness of the
test fluid towards the VitonTM fluoroelastomer specimen. Under the test conditions
described, fluids resulting in a reduction of more than 45% of the original
(untreated) %ELB value (expressed as %ELB Change = -45%) were considered to be
very aggressive towards the sample tested and, therefore, incompatible with the
YitonTM fluoroelastomer engine seal. Values of %~LB Change of zero to -5% were
representative of neutral conditions and, therefore, compatible with the engine
seals. Values of %ELB Change of about -20% or less, i.e., more negative, indicated
poor seal compatibility. The %ELB results are greatly affected by the rnanner inwhich the equipment is used and it is important to include comparative untreatedsample results with each new set of immersion test samples.
Performance characteristics in the Engine Seal Compatibility Test of the
lubricating oil additives of the present invention and those representing
commercial nitrogen-containing oil additives are presented in Table 3. Samples of
VitonTM fluoroelastomer were immersed in test fluids containing the additives
listed. %ELB Change values are expressed as the average for three specimens tested
in each fluid. In all cases the test fluids contained 1.5% OLOATM 267 (component of
commercial detergent-irlhibitor (DI) package available from Chevron Chemicals).
A-Comparative: Commercial poly(alkyl methacrylate) nitrogen-containing
viscosity index improver
B-Comparative: Commercial polyolefin nitrogen-containing viscosity
index improver
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Compositions C through H represent polymeric additives (monomer type
and relative parts by weight indicated) of the present invention (MMA is methyl
methacrylate, IDMA is isodecyl methacrylate, CEMA is cetyl-eicosyl methacrylate,LMA is lauryl-myristyl methacrylate, HPMA is hydroxypropyl methacrylate):
C MMA/LMA/HEMA (8/88/4)
D MMA/IDMA/CEMA/HPMA (10/56/30/4)
E MMA/IDMA/CEMA/HPMA (10/56/30/4)
F MMA/IDMA/CEMA/HPMA (10/56/29/5)
G MMA/IDMA/CEMA/HPMA (10/56/29/5)
H MMA/IDMA/CEMA/HPMA (9/53/29/9)
TABLE 3
~ngine Se~l Compatibility Te$t
Additive Tvpe %ELB Change
A-Comparative Nitrogen-containing -47
B-Comparative Nitrogen-containing -39
C 4% HEMA 0
D 4% HPMA -2
E 4% HPMA -1
F 5% HPMA 3
G 5% HPMA -2
H 9% HPMA -3
EXAMPLE 7
Performance characteristics in the Cold-Cranking Simulator (CCS) test for the
lubricating oil additives of the present invention are presented in Table 4. Blends of
the additives to be tested in a base oil were prepared by mixing 2.24% ~active) of the
polymer additive and 11.4% of DI package (available from Lubrizol Company as
LZ-7838G) with a calculated amount of 100N oil. For example, if the polymer
additive is available as 50% solids in 100N oil, then 4.48 parts of the polymer
additive oil solution was mixed with 11.4 parts of LZ-7838G and 84.12 parts of 100N
oil to produce the final oil composition to be tested. The CCS viscosity specification
for an SAE 5W-30 grade oil is less than 35 poise at -25C.
23
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TABLE 4
Cold-Cranlcing Simulal:or (C(:~$) Te~t
Polymer Additive Composition CCS Viscosity
% MMA % IDMA % CEMA % HPh~A Poise ~ -25~C
0 70 30 0 3~.9
0 65 30 5 34.5
0 60 30 1() 3~L.2
65 30 0 34.0
60 30 5 33.6
55 30 10 32.5
60 30 0 36.0
55 30 5 33.8
50 30 10 33.g
EXAMPLE 8
Apparent viscosity by mini-rotary viscometer (MRV) was determined by
two different test methods and is a measure of engine oil pumpability after cold-
engine startup. ASTM D-3829-87 deals with viscosity measurement in the 0 to -40C
temperature range and describes the standard MRV test. ASTM D-4684-89 deals
with viscosity measurement in the temperature range of -15 to -30C and describes
the TP-1 MRV test. Table 5 contains data for 2 sets of 5 different SAE 5W-30 oilformulations, using 5 different commercial base oils. One set uses a commercial
poly(alkylmethacrylate) type nitrogen-containing viscosity index improver and the
other set uses a poly(10 MMA/55 IDMA/30 CEMA/5 HPMA) additive composition
of the present invention. SAE J300 Engine Oil Viscosity Classification (January 1991)
allows a maximum of 300 poise at -30C for SAE 5W-30 oil using the ASTM D-4684-
89 test procedure.
24
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TABLE 5
MRV_Pumpability Test
Source of
Viscosity Index $ource of Viscosity at -30C, poise
Improver Base Oil TP-1 MRV Std MRV
Commercial A 85.3 74.1
Commercial B 78.4 74.5
Commercial C 72.2 66.1
Commercial . D 64.2 64.2
Commercial E 73.1 71.2
Invention A 86.9 67.8
Invention B 75.7 73.5
Invention C 62.8 63.5
Invention D 60.4 57.2
Invention E 61.2 63.7
A - Solvent-extracted 100N base oil
B - Solvent-extracted, solvent dewaxed 100N base oil
C - Hydrocracked, catalytically dewaxed 100N base oil
D - Solvent extracted, solvent dewaxed 100N base oil
E - Solvent extracted, hydrofinished, solvent dewaxed 100N base oil~
. .
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