Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components
Reexamination Certificate
2001-11-19
2004-03-30
Toomer, Cephia D. (Department: 1714)
Compositions
Heat-exchange, low-freezing or pour point, or high boiling...
Organic components
C508S469000, C526S078000, C526S328000, C526S329500
Reexamination Certificate
active
06712991
ABSTRACT:
TECHNICAL FIELD
The present invention relates to certain poly(alkyl (meth)acrylates) useful as viscosity index improving additives for hydraulic fluids.
BACKGROUND
Hydraulic systems, e.g., systems wherein the operation of high speed, high pressure hydraulic pumps is subject to wide temperature variations, can impose severe demands on hydraulic fluids.
Additives for improving the properties, e.g., the viscosity index, of hydrocarbon base oils used in hydraulic fluids are known. Viscosity index improving additives reduce the influence of temperature changes on fluid viscosity. British Patent GB 1,172,697 discloses viscosity index improving copolymers of up to 50 weight % “readily polymerizable” monoethylenically unsaturated monomers, e.g., styrene, t-butyl methacrylate, methyl methacrylate and mixtures thereof, with at least 50 weight % “difficulty polymerizable” monoethylenically unsaturated monomers, e.g., lauryl methacrylate. U.S. Pat. No. 5,112,509 discloses a method for making a poly(methyl methacrylate-co-lauryl methacrylate) copolymer for use in hydraulic fluids and lubricating oil compositions as a viscosity index improver. The process includes heating a reaction mixture of the monomers and a polymerization initiator to a temperature from 200° F. to 300° F.
Paraffinic oils have a tendency to gel at low temperatures due to ordering of wax molecules in the oil. In some hydraulic systems, e.g., mobile equipment, startup temperatures may be well below 0° F. and it is critically important that the hydraulic fluid in the system remains fluid at the low temperatures encountered. High performance hydraulic fluid compositions for applications involving low startup temperatures typically include a pour point depressing additive, in addition to a viscosity index improving additive, to improve the low temperature fluidity of the hydraulic fluid.
Along with their several advantageous effects, known poly(alkyl (meth)acrylate) viscosity index improvers can impart at least one undesirable property to the hydraulic fluids in which they are used. Hydraulic fluids formulated with such additives have shown a tendency to form emulsions with ambient moisture during use. The performance of the emulsified fluids is compromised with respect to, e.g., lubricity, corrosion resistance, low temperature performance and compressibility. In addition, the presence of small amounts water in hydraulic fluids has been found to detrimentally effect the filterability of such fluids. Reduced filterability may result in plugging of hydraulic system filters.
SUMMARY OF THE INVENTION
A method for making a copolymer for improving the viscosity index of a hydraulic fluid is disclosed. The method includes the steps of:
heating a reaction mixture to a reaction temperature from about 75° C. to about 100° C., said reaction mixture comprising:
from about 55 weight percent to about 99.5 weight percent of a first monomer selected from the group consisting of (C
8
-C
5
)alkyl (meth)acrylates and mixtures thereof;
from about 0.5 weight percent to about 45 weight percent of a second monomer selected from the group consisting of (C
1
-C
7
)alkyl (meth)acrylates, (C
16
-C
24
)alkyl (meth)acrylates and mixtures thereof;
an effective amount of a polymerization initiator; and
a hydrocarbon diluent; and
maintaining the reaction mixture at the reaction temperature for a period of time effective to allow copolymerization the monomers. Copolymers made by the process of the present invention provide viscosity index improvement to the hydraulic fluids in which they are used while providing improved demulsibility and filterability relative to viscosity index improving additives made by known processes.
DETAILED DESCRIPTION OF THE INVENTION
The copolymer of the present invention includes from about 55 weight percent (wt %) to about 99.5 wt % repeating units, each having the structural formula (1):
wherein each occurrence of R
1
is H or methyl and each occurrence of R
2
is independently selected from the group consisting of (C
8
-C
15
)alkyl and from 0.5 wt % to about 45 wt % repeating units selected from the group consisting of repeating units of the structural formulae (2), (3) or (4) disclosed below, and mixtures thereof. As used herein, the term “copolymer” means a polymer having more than one type of repeating unit and includes, e.g., copolymers, terpolymers and tetrapolymers.
Preferably, R
1
is methyl.
As used herein, (C
8
-C
15
) alkyl means any straight or branched alkyl group having 8 to 15 carbon atoms per group, e.g., octyl, nonyl, decyl, isodecyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl. Preferably, R
2
is(C
10
-C
15
)alkyl. More preferably, R
2
is selected from the group consisting of isodecyl, lauryl, tridecyl, myristyl, pentadecyl and mixtures thereof.
The copolymer of the present invention includes from about 0 wt % to about 45 wt % repeating units, each having the structural formula (2):
wherein each occurrence of R
3
is independently H or methyl and each occurrence of R
4
is independently n-butyl, isobutyl or t-butyl.
The copolymer includes from about 0 wt % to about 20 wt % repeating units, each having the structural formula (3):
wherein each occurrence of R
5
is independently H or methyl. Preferably, R
5
is methyl.
The copolymer includes from about 0 wt % to about 35 wt % repeating units, each having the structural formula (4):
wherein each occurrence of R
7
is independently H or methyl and each occurrence of R
8
is independently selected from the group consisting of (C
16
-C
24
) alkyl.
Preferably, R
7
is methyl.
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, heptadecyl, cetyl, nonadecyl, eicosyl. Preferably, and R
8
is (C
16
-C
20
)alkyl. More preferably, R
8
is selected from the group consisting of stearyl, cetyl, eicosyl and mixtures thereof.
The copolymer of the present invention has a number average molecular weight, determined, e.g., by gel permeation chromatography, between about 15,000 and about 120,000, preferably between about 20,000 and about 100,000, and most preferably between about 25,000 and about 75,000.
The copolymer of the present invention has a weight average molecular weight, determined, e.g., by gel permeation chromatography, between about 25,000 and about 225,000, preferably between about 37,500 and about 225,000, and most preferably between about 50,000 and about 200,000.
In a preferred embodiment, the copolymer includes from about 55 wt % to about 99.5 wt % repeating units of the structural formula (1) and from about 0.5 wt % to about 45 wt % repeating units of the structural formula (2). More preferably, the copolymer includes from about 60 wt % to about 90 wt % repeating units of the structural formula (1) and from about 10 wt % to about 40 wt % repeating units of the structural formula (2). Even more preferably, the copolymer includes from about 70 wt % to about 85 wt % repeating units of the structural formula (1) and from about 15 wt % to about 30 wt % repeating units of the structural formula (2).
In a second preferred embodiment, the copolymer includes from about 55 wt % to about 98.5 wt % repeating units of the structural formula (1) from about 0.5 wt % to about 44 wt % repeating units of the structural formula (2) and from about 1 wt % to about 20 wt % repeating units of the structural formula (3). More preferably, the copolymer includes from about 60 wt % to about 87.5 wt % repeating units of the structural formula (1) from about 10 wt % to about 37.5 wt % repeating units of the structural formula (2) and from about 2.5 wt % to about 17 wt % repeating units of the structural formula (3). Still more preferably, the copolymer includes from about 70 wt %, to about 80 wt % repeating units of the structural formula (1) from about 15 wt % to about 25 wt % repeating units of the structural formula (2) and from about 5 wt % to about 15 wt % repeating units of the structural formula (3)
In a third preferred embodiment, the copolymer includes from about 55 wt % to about 97 wt % re
Gore Robert H.
Stevens Bridget M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rohmax Additives GmbH
LandOfFree
Method of making a copolymer useful as viscosity index... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of making a copolymer useful as viscosity index..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making a copolymer useful as viscosity index... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3251241