Note: Descriptions are shown in the official language in which they were submitted.
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Improved process for preparing continuously variable-composition
copolymers
Description
The present invention relates to an improved process for preparing
continuously
variable-composition copolymers by effecting gradual changes in monomer com-
position during the polymerization process. An example of application of this
proc-
ess is the preparation of poly(meth)acrylate copolymers that have improved
lubri-
cating oil additive properties, for example, as pour point depressants or
viscosity
index improvers, when compared to related polymer additives made by conven-
tional means.
The behavior of petroleum oil formulations under cold flow conditions is
greatly in-
fluenced by the presence of paraffins (waxy materials) that crystallize out of
the oil
upon cooling; these paraffins significantly reduce the fluidity of the oils at
low tem-
perature conditions. Polymeric flow improvers, known as pour point
depressants,
have been developed to effectively reduce the "pour point" or solidifying
point of
oils under specified conditions (that is, the lowest temperature at which the
formu-
lated oil remains fluid). Pour point depressants are effective at very low
concen-
trations, for example, between 0.05 and 1 percent by weight in the oil. It is
be-
lieved that the pour point depressant material incorporates itself into the
growing
paraffin crystal structure, effectively hindering further growth of the
crystals and
the formation of extended crystal agglomerates, thus allowing the oil to
remain
fluid at lower temperatures than otherwise would be possible.
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One limitation of the use of pour point depressant polymers is that petroleum
base
oils from different sources contain varying types of waxy or paraffin
materials and
not all polymeric pour point depressants are equally effective in reducing the
pour
point of different petroleum oils, that is, a polymeric pour point depressant
may be
effective for one type of oil and ineffective for another. It would be
desirable for a
single pour point depressant polymer to be useful in a wide variety of
petroleum
oils.
One approach to solving this problem is disclosed in "Depression Effect of
Mixed
Pour Point Depressants for Crude Oil" by B. Zhao, J. Shenyang, Inst. Chem.
Tech., 8(3), 228-230 (1994), where improved pour point performance on two dif-
ferent crude oil samples was obtained by using a physical mixture of two
different
conventional pour point depressants when compared to using the pour point de-
pressants individually in the oils. Similarly, U.S. 5,281,329 and European
Patent
Application EP 140,274 disclose the use of physical mixtures of different poly-
meric additives to achieve improved pour point properties when compared to us-
ing each polymer additive alone in lubricating oils.
U.S. 4,048,413 discloses a process for the preparation of uniform-composition
copolymers by controlling the ratio and rate of addition of the monomers added
to
a polymerizing mixture of the monomers to offset the natural differences in
reactiv-
ities of the individual monomers that would normally lead to compositional
"drift"
during conventional polymerizations. There is no disclosure in U.S. 4,048,413
of
controlling the ratio and rate of addition of monomers to a polymerization
mixture
to provide a continuously changing- or continuously variable-composition
copoly-
mer.
Document WO 2006/015751 presents a method for free radical polymerization
where a monomer mixture is heated to an elevated temperature and initiator is
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added dropwise over multiple steps, with a greater rate of initiator addition
in the
latter steps.
None of these previous approaches provides good low temperature fluidity when
a single polymer additive is used in a wide range of lubricating oil
formulations.
Furthermore, US 6,140,431 presents a process to produce continuously variable-
composition methacrylate copolymers by forming two different reaction
mixtures,
each mixture containing polymerization free radical initiators and gradually
adding
either (a) reaction mix "A" to a mixing vessel while reaction mix "B" is being
added
to mix "A" and the content of the mixing vessel is being fed to the reaction
vessel
or (b) reaction mix "A" to the reactor at one feed profile while reaction mix
"B" is
also being added to the reactor at a different feed profile. US 6,140,431 does
not
disclose to provide a high amount of a specific monomer mixture to the
reaction
vessel before starting the addition of another monomer mixture.
The copolymers obtainable according to US 6,140,431 show a good efficiency as
pour point depressants. However, the process is difficult to control and needs
a
high investment. Based on the complexity of the process, the risk of mistakes
is
high.
It is an object of the present invention to provide an improved process for
prepar-
ing copolymers having a continuously variable-composition. A further object of
the
present invention is to provide a process being easy to control. Additionally,
the
process should be performed at a low risk of mistakes. Furthermore, it is an
object
of the present invention to provide a simple and inexpensive process for
preparing
copolymers having a continuously variable-composition.
These as well as other not explicitly mentioned tasks, which, however, can
easily
be derived or developed from the introductory part, are achieved by the
process
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for preparing continuously variable composition copolymers according to
present
claim 1. Expedient modifications of the process in accordance with the
invention
are described in the dependent claims.
The present invention provides a process for preparing continuously variable
composition copolymers comprising:
(a) providing a reaction vessel comprising a first monomer composition;
(b) providing a feed vessel comprising a second monomer composition;
(c) initiating a polymerization reaction in said reaction vessel;
(d) continuing the polymerization reaction during the gradual addition of said
sec-
ond monomer composition from said feed vessel to said reaction vessel wherein
the gradual addition of the second monomer composition is performed such that
continuously variable composition copolymers are achieved;
(e) maintaining said polymerization until at least 90 % of the total monomer
com-
position has been converted to a copolymer;
wherein said copolymer has a weight average molecular weight from 10,000 to
1,000,000; said copolymer is soluble in lubricating oil; and the monomers pro-
vided in the reaction vessel by said first monomer composition composes at
least
50 % by weight of all the monomers used to prepare said copolymer.
The process of the invention provides an improved process for preparing copoly-
mers having a continuously variable-composition. The process of the present in-
vention can easily be controlled. Therefore, the process can be performed at a
low risk of mistakes. Furthermore, the process to prepare continuously
variable
polymer compositions is very simple and inexpensive. This is very important
with
regard to the return of investment and up scaling of a plant for the
production of
the copolymers mentioned above. Additionally, the process of the present inven-
tion needs a reduced amount of initiator used. Moreover, the invention
provides
an improved process temperature control, and increased process reliability.
Fur-
thermore, the copolymers prepared by the process of the present invention have
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the aforementioned desired combination of lubricating oil properties in a
single
polymer additive.
According to the process of the present invention, a first monomer composition
is
provided in a reaction vessel. Additionally, a second monomer composition is
pro-
vided in a feed vessel. The expression "reaction vessel" means the reactor in
which the polymerization reaction takes place. Useful reaction vessels are
well
known in the art. The term "feed vessel" expresses a reservoir from which the
second monomer mixture is added to the reaction vessel.
The first monomer composition is different than the second monomer
composition.
For example, the first monomer composition may comprise a monomer which is
not present in the second monomer composition or the second monomer composi-
tion may comprise a monomer which is not present in the first monomer composi-
tion. Additionally, both monomer compositions may comprise the same monomers.
However, the monomers are present in different amounts.
According to a preferred embodiment the first monomer composition can contain
one or multiple polymerizable monomers, identified as A1, B1, C1, ... X1,
where
the sum of the weight percentages of each polymerizable monomer adds up to
100. The second monomer composition can also contains one or multiple poly-
merizable monomers, identified as A2, B2, C2, ... Xn, where the sum of the
weight
percentages of each polymerizable monomer adds up to 100. Similarly,
additional
monomer composition can be used as additional feed compositions. In this way,
continuously variable polymer compositions can be prepared where the initial
polymer compositions are equivalent to the first monomer composition,
identified
as A1, B1, C1, ... X1. The polymer composition then varies over the course of
the
reaction starting at the time that the second monomer composition feed is
begun,
such that the average composition can be defined by the equations:
Aavg=7- (An*Wn)/7- Wn
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Bavg-7- (Bn*Wn7- Wn
Cavg = 7- (Cin ~ Wn 7- Wn . . . .
Xavg=7- (Xn*Wn7- Wn
where Xn is the weight percent of each individual monomer (X) in each monomer
composition (n) and Wn is the total weight of monomer in that monomer composi-
tion.
The final polymer composition produced is equivalent to the unreacted monomer
composition present in the reaction vessel at the point where all monomer
feeds
are completed. Thus, the range of compositions in the final polymer can be
esti-
mated as ranging between:
Aavg + [Aavg - A, ] and Aavg - [Aavg - A1]
Bavg +[Bavg - B1] and Bavg -[Bavg - B1]
Cavg +[Ciavg - Ci j] a n d Ciavg -[Ciavg - Ci i] ...
Xavg + [Xavg - X, ] and Xavg - [Xavg - X1]
where [AaVg- A,] is the absolute value of the difference between the starting
com-
position (A,) and the average composition (Aavg) for monomer A, with
equivalent
definitions for the other monomers.
According to a preferred embodiment the concentration of at least one monomer
component in the first monomer composition differs preferably in at least 5%,
more preferably at least 10% and more preferably at least 5-50 % from the con-
centration of the same monomer component in the second monomer composition.
The difference between the first and second monomer compositions can be de-
fined by the sum of the differences of each individual monomer and can be de-
fined by the equation:
XDiff =7- IX1-X21 where Xi the weight percent of each individual monomer in
the first
monomer composition and X2 the weight percent of each individual monomer in
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the second monomer composition. In the preferred embodiment, the value for
XDiff
can range from 5% to 200% and more preferably range from 10% to 100%.
Using standard polymerization kinetics, one can estimate the instantaneous co-
polymer compositions as a function of polymer formation based on the first
monomer composition and the second monomer composition and feed rate. Fig-
ure 1 provides such an estimate for the case where the starting monomer compo-
sition of 71.4 parts with A1= LMA = 30% and B1= SMA = 70% and the second
monomer composition of 28.6 parts with A2 = LMA = 100%.
Note: LMA = lauryl-myristyl methacrylate, SMA = cetyl-stearyl methacrylate
In the preferred embodiment, the absolute range of compositions of at least
one of
the monomers is at least 5%, with a more preferable range of 5 - 30%, and a
maximum range as high as 100%.
There is no limitation on the number of monomers or monomer types used to pre-
pare continuously variable-composition copolymers of the present invention.
Monomers used in practicing the process of the present invention may be any
monomers capable of polymerizing with comonomers and which are relatively
soluble in the copolymer formed. Preferably the monomers are monoethylenically
unsaturated monomers. Polyethylenically unsaturated monomers which lead to
crosslinking during the polymerization are generally undesirable.
Polyethylenically
unsaturated monomers which do not lead to crosslinking or only crosslink to a
small degree, for example, butadiene, are also satisfactory comonomers.
One class of suitable monoethylenically unsaturated monomers is vinylaromatic
monomers that includes, for example, styrene, a-methylstyrene, vinyltoluene,
or-
tho-, meta- and para-methylstyrene, ethylvinylbenzene, vinylnaphthalene and vi-
nylxylenes. The vinylaromatic monomers can also include their corresponding
substituted counterparts, for example, halogenated derivatives, that is,
containing
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one or more halogen groups, such as fluorine, chlorine or bromine; and nitro,
cyano, alkoxy, haloalkyl, carbalkoxy, carboxy, amino and alkylamino
derivatives.
Another class of suitable monoethylenically unsaturated monomers is nitrogen-
containing ring compounds, for example, vinylpyridine, 2-methyl-5-
vinylpyridine,
2-ethyl-5-vinylpyridine, 3-methyl-5-vinylpyridine, 2,3-dimethyl-5-
vinylpyridine, 2-
methyl-3-ethyl-5-vinylpyridine, methyl-substituted quinolines and
isoquinolines, 1-
vinylimidazole, 2-methyl-1 -vinylimidazole, N-vinylcapro-lactam, N-
vinylbutyrolactam and N-vinylpyrrolidone.
Another class of suitable monoethylenically unsaturated monomers is ethylene
and substituted ethylene monomers, for example: a-olefins such as propylene,
isobutylene and long chain alkyl a-olefins (such as (C10 -C20)alkyl a-
olefins); vi-
nyl alcohol esters such as vinyl acetate and vinyl stearate; vinyl halides
such as
vinyl chloride, vinyl fluoride, vinyl bromide, vinylidene chloride, vinylidene
fluoride
and vinylidene bromide; vinyl nitriles such as acrylonitrile and
methacrylonitrile;
(meth)acrylic acid and derivatives such as corresponding amides and esters;
maleic acid and derivatives such as corresponding anhydride, amides and
esters;
fumaric acid and derivatives such as corresponding amides and esters; itaconic
and citraconic acids and derivatives such as corresponding anhydrides, amides
and esters.
A preferred class of (meth)acrylic acid derivatives is represented by alkyl
(meth)acrylate, substituted (meth)acrylate and substituted (meth)acrylamide
monomers. Each of the monomers can be a single monomer or a mixture having
different numbers of carbon atoms in the alkyl portion. Preferably, the
monomers
are selected from the group consisting of (C1 -C24)alkyl (meth)acrylates, hy-
droxy(C2 -C6)alkyl (meth)acrylates, dialkylamino(C2 -C6)alkyl (meth)acrylates
and dialkylamino(C2 -C6)alkyl (meth)acrylamides. The alkyl portion of each
monomer can be linear or branched.
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Particularly preferred polymers useful in the process of the present invention
are
the poly(meth)acrylates derived from the polymerization of alkyl
(meth)acrylate
monomers. As used herein, the term "alkyl (meth)acrylate" refers to either the
cor-
responding acrylate or methacrylate ester; similarly, the term "(meth)acrylic"
refers
to either the corresponding acrylic or methacrylic acid and derivatives.
Examples
of the alkyl (meth)acrylate monomer where the alkyl group contains from 1 to 6
carbon atoms (also called the "low-cut" alkyl (meth)acrylates), 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 the alkyl (meth)acrylate monomer where the alkyl group contains
from 7 to 15 carbon atoms (also called the "mid-cut" alkyl (meth)acrylates),
are 2-
ethylhexyl acrylate (EHA), 2-ethylhexyl methacrylate, octyl methacrylate,
decyl
methacrylate, isodecyl methacrylate (IDMA, based on branched (C1O)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), a mixture of linear and
branched isomers of dodecyl, tridecyl, tetradecyl and pentadecyl
methacrylates;
and lauryl-myristyl methacrylate (LMA), a mixture of dodecyl and tetradecyl
methacrylates. The preferred mid-cut alkyl methacrylates are lauryl-myristyl
methacrylate, dodecyl-pentadecyl methacrylate and isodecyl methacrylate.
Examples of the alkyl (meth)acrylate monomer where the alkyl group contains
from 16 to 24 carbon atoms (also called the "high-cut" alkyl (meth)acrylates),
are
hexadecyl methacrylate (also known as cetyl methacrylate), heptadecyl methacry-
late, octadecyl methacrylate (also known as stearyl methacrylate), nonadecyl
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methacrylate, eicosyl methacrylate, behenyl methacrylate and combinations
thereof. Also useful are: cetyl-eicosyl methacrylate (CEMA), a mixture of
hexade-
cyl, octadecyl, and eicosyl methacrylate; and cetyl-stearyl methacrylate
(SMA), a
mixture 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 (meth)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 10 and 15 or
16
and 20 carbon atoms in the alkyl group. Consequently, for the purposes of this
in-
vention, alkyl (meth)acrylate is intended to include not only the individual
alkyl
(meth)acrylate product named, but also to include mixtures of the alkyl
(meth)acrylates with a predominant amount of the particular alkyl
(meth)acrylate
named. The use of these commercially available alcohol mixtures to prepare
(meth)acrylate esters results in the LMA, DPMA, SMA and CEMA monomer types
described above. Preferred (meth)acrylic acid derivatives useful in the
process of
the present invention are methyl methacrylate, butyl methacrylate, isodecyl
methacrylate, lauryl-myristyl methacrylate, dodecyl-pentadecyl methacrylate,
cetyl-eicosyl methacrylate and cetyl-stearyl methacrylate.
For the purposes of the present invention, it is understood that copolymer
compo-
sitions representing combinations of the monomers from aforementioned classes
of monomers may be prepared using the process of the present invention. For ex-
ample, copolymers of alkyl (meth)acrylate monomers and vinylaromatic mono-
mers, such as styrene; copolymers of alkyl (meth)acrylate monomers and substi-
tuted (meth)acrylamide monomers, such as N,N-dimethylaminopropyl
methacrylamide; copolymers of alkyl (meth)acrylate monomers and monomers
based on nitrogen-containing ring compounds, such as N-vinylpyrrolidone; co-
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polymers of vinyl acetate with fumaric acid and its derivatives; and
copolymers of
(meth)acrylic acid and its derivatives with maleic acid and its derivatives.
The process of the present invention provides a means of preparing a mixture
of a
large number of copolymer compositions in a single operation by controlling
the
introduction of individual monomers or monomer types into the polymerizing me-
dium during polymerization. As used herein, "monomer type" refers to those
monomers that represent mixtures of individual closely related monomers, for
ex-
ample, LMA (mixture of lauryl and myristyl methacrylates), DPMA (a mixture of
dodecyl, tridecyl, tetradecyl and pentadecyl methacrylates), SMA (mixture of
hexadecyl and octadecyl methacrylates), CEMA (mixture of hexadecyl, octadecyl
and eicosyl methacrylates). For the purposes of the present invention, each of
these mixtures represents a single monomer or "monomer type" when describing
monomer ratios and copolymer compositions. For example, a copolymer de-
scribed as having a 70/30 LMA/CEMA composition is considered to contain 70%
of a first monomer or monomer type (LMA) and 30% of a second monomer or
monomer type (CEMA), although it is understood that the copolymer contains at
least 5 different individual monomers (lauryl, myristyl, hexadecyl, octadecyl
and
eicosyl methacrylates).
As used herein, all percentages referred to will be expressed in weight
percent
(%), based on total weight of polymer or composition involved, unless
specified
otherwise.
Preferably, the second monomer composition is directly and gradually added
from
the feed vessel to the reaction vessel. The expression directly means that the
second monomer composition is added to the reaction vessel without using a fur-
ther mixing vessel.
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Preferably, the first monomer composition comprises at least two monomers
and/or the second monomer composition comprises at least two monomers. Ac-
cording to a preferred embodiment of the present invention, the first monomer
composition comprises more different monomers than the second monomer com-
position; especially the first monomer composition may comprise at least one
monomer, more preferably at least two monomers which are not present in the
second monomer composition.
As used herein, the term "copolymer" or "copolymer material" refers to polymer
compositions containing units of two or more monomers or monomer types. As
used herein, the term "continuously variable-composition" refers to a
copolymer
composition where there is a distribution of single-composition copolymers
within
a copolymer material, that is, a copolymer material derived from a single
polym-
erization process. The distribution of single-composition copolymers must be
such
that no more than 50%, and preferably no more than 20% of any single-
composition copolymer is represented within the distribution range of single-
composition copolymers in the copolymer material and at least four, preferably
at
least 5 and more preferably at least 10, different single-composition
copolymers
comprise the continuously-variable composition copolymer.
For the purposes of the present invention, a copolymer having a continuously-
variable composition is defined as having a difference of at least 5%,
preferably
between 5% and 30% in at least one of the monomer or monomer type compo-
nents of the single-composition copolymers of the copolymer composition range
while satisfying the aforementioned requirement that no more than 50% of any
single-composition copolymer is present in the copolymer material. A single-
composition copolymer is defined as a copolymer differing from its nearest
most
similar copolymer by at least 1 % in at least one monomeric component.
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For example, in a copolymer material containing single-composition copolymers
ranging from 70 Monomer A/30 Monomer B to 30 Monomer A/70 Monomer B
(prepared by a polymerization using an initial 70 A/30 B monomer mix and grad-
ual addition of Monomer B to the polymerizing monomer mixture until it is 30 A
/70 B at the end of the monomer feed), the 61 A /39 B component is considered
a
single-composition copolymer and the 62 A /38 B component is considered a dif-
ferent single-composition copolymer. Using this example to further illustrate
the
concept of continuously variable-composition copolymers, the aforementioned co-
polymer composition would theoretically contain at least 40 different single-
composition copolymers, each differing by 1 % between 70 A/30 B and 30 A /70 B
based on the theoretical formation of each single-composition copolymer during
the polymerization, assuming the composition of the monomer feed being polym-
erized had been continuously adjusted throughout the polymerization process
from one extreme of A/B composition to the other extreme of A/B composition.
In
this case, the copolymer material can be described as theoretically having
about
2.5% each of 40 different single-composition copolymers, each differing by suc-
cessive increments of 1% A and 1% B
As used herein, "theoretical formation" corresponds to the composition and a-
mount (weight %) of a specific single-composition copolymer formed as a
fraction
of the entire range of copolymer compositions available. This is based on the
as-
sumption that the composition of the instantaneous polymer formed is
equivalent
to the unreacted monomer composition present in the reaction vessel at the
time
that the copolymer is formed. Thus, the initial single-composition copolymer
pre-
pared is equivalent to the first monomer composition described in Step (a),
which
can be identified as A1, B1, C1, ... X1. The unreacted monomer composition pre-
sent in the reaction vessel than changes with the start of gradual addition of
the
second monomer composition as described in Step (d) and with removal of avail-
able monomer from the reaction vessel as copolymerization occurs. As used
herein, the term "gradual addition" refers to continuous or intermittent
addition of
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monomer, monomer mixture or monomers over a period of time, dropwise or in a
stream. As used herein, "intermittent" addition includes the brief
interruption of the
addition of monomer feed to the reactor or in-line mixing device so long as
the in-
terruption corresponds to a theoretical formation of no more than about 50% of
a
single-composition copolymer (based on monomer ratio in the reactor) within
the
range of copolymer compositions formed during the polymerization. Intermittent
addition may also include multiple discrete additions of monomers or monomer
mixtures, where the compositions of the monomer mixture at each discrete addi-
tion differs from at least one of the compositions of the other discrete
additions by
at least 5% in one or more components of the monomer mixture and the maximum
contribution of any discrete monomer addition corresponds to less than 50% of
a
single-composition copolymer (based on monomer ratio in the reactor) within
the
range of copolymer compositions formed during the polymerization.
Preferably, the gradual addition of the one or more additional monomer
mixtures
in step (d) is conducted such that the addition begins before 50% of the first
monomer mixture is converted to copolymer, and preferably before 25% is con-
verted, and most preferably before 10% is converted. The one or more
additional
monomer mixtures is added at a rate such that at the end of the addition, at
least
50% of the total monomers is converted to copolymers, and preferably at least
75% is converted, and most preferably at least 90% is converted.
As used herein, "under polymerization conditions" refers to conditions within
the
polymerization reactor sufficient to produce substantial incorporation of any
monomers present into copolymer; that is, for example, the combination of tem-
perature, type of free-radical initiator, and any optional promoter, provides
an en-
vironment where the half-life of the initiator system is less than about 2
hours,
preferably less than 1 hour, more preferably less than 10 minutes and most
pref-
erably less than about 5 minutes.
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In step (c) the polymerization reaction in the reaction vessel is usually
initiated by
a free radical initiator. The initiation can be achieved, e.g. by raising the
tempera-
ture if an initiator is present in the reaction vessel. Preferably, the
initiation is
achieved either through gradual addition of a free radical initiator to the
reaction
vessel or by inclusion of a free radical initiator into the second monomer
composi-
tion after the desired reaction temperature has been achieved.
The process is directed towards producing a single continuously variable-
composition copolymer in contrast to the preparation (in separate polymeriza-
tions) of different copolymers that are then combined to produce a physical
mix-
ture of single-composition copolymers (see U.S. 5,281,329 and European Patent
Application EP 140,274). In this way, copolymers may be conveniently tailored
to
the specific end-use applications required of them without the need for
multiple
polymerization reactions and the isolation and storage of different copolymers
to
provide combination additive compositions.
There is no limitation on the extremes of the range of individual compositions
within a given copolymer material prepared by the process of the present inven-
tion. For example, a copolymer material having an overall average composition
of
50 A/50 B may be composed of individual single-composition copolymers ranging
from 100 NO B to 0 A/100 B or only from 55 A/45 B to 45 A/55 B. In a similar
fash-
ion, a copolymer material having an overall average composition of 80 A /10 B
/10
C (where C represents a third monomer) may be composed of individual single-
composition copolymers ranging from, for example, 100 A /0 B /0 C to 60 A /20
B
/20 C or only from 75 A/20 B/5 C to 85 A/O B/15 C.
An advantage of the process of the present invention is the ability to easily
vary
the number of different single-composition copolymers formed within a single
po-
lymerization process. In addition, for a copolymer with the same range of
individ-
ual single-composition copolymers as described above, the absolute number and
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distribution of the single-composition copolymers formed within a the
polymeriza-
tion process can be varied by varying parameters during the reaction such as
re-
action temperature, initiator feed rate, and/or the feed rate of the second
and sub-
sequent monomer mixtures. Using standard polymerization kinetics, one can es-
timate the instantaneous copolymer compositions as a function of polymer forma-
tion based on the first monomer composition and the second monomer composi-
tion using different feed rates for the second monomer composition. Figure 1
pro-
vides such an estimate for the case where the starting monomer composition of
71.4 parts with A1= 30% and B1= 70% and the second monomer composition of
28.6 parts with A2 = 100%. This is equivalent to an overall average
composition of
50 A/50 B and overall compositions of between 30 A /70 B and 70 A/30 B. As il-
lustrated in Figure 2, the instantaneous polymer composition produced
throughout
the copolymerization process varies as a function of the feed rate of the
second
monomer to the polymerization reactor. Similar variations are observed by
varying
the rate and/or amount of initiator addition and by varying the polymerization
tem-
perature.
The process of the invention may have multiple monomer feeds which can have
different feed rates in order to control the incorporation of monomers of
signifi-
cantly different reactivities, such as (meth)acrylic esters and styrene
derivatives. If
desired, control of copolymer composition can be derived from application of
the
well-known copolymer equation based on the use of monomer reactivity ratios
(Textbook of Polymer Science by F. W. Billmeyer, Jr., pp 310-325 (1966)). U.S.
Pat. No. 4,048,413 discloses the use of monomer reactivity ratios and addition
of
increasing amounts of the more reactive monomer component of the desired co-
polymer during the polymerization to achieve a constant-composition copolymer.
In contrast to the teachings and objects of U.S. No. 4,048,413, the process of
the
present invention is directed to providing continuously-changing composition
or
continuously-variable composition copolymers during a single polymerization
process.
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Preferably, the process of the present invention is practiced to prepare
copolymer
materials having a large number of individual single-composition copolymers,
the
range being represented by extremes in copolymer composition established by
the monomer feed conditions and monomer ratios. Variations in the composition
of the monomer feeds during the polymerization are not limited to being
uniformly
increased or decreased from an initial composition proceeding towards a speci-
fied final composition. All that is necessary is that the overall requirements
defin-
ing the preparation of a continuously variable-composition copolymer be
satisfied:
(1) no single-composition copolymer composition may represent more than 50%
of the copolymer material within the range of single-composition copolymers de-
fining the copolymer material,
(2) the copolymer material must contain individual single-composition
copolymers
having a difference of at least 5% between at least one of the monomer or mono-
mer type components of the single-composition copolymers,
(3) the copolymer material must contain at least four different single-
composition
copolymers, and
(4) a single-composition copolymer is defined as having a composition
differing
from its nearest most similar composition by at least 1 % in at least one
monomeric
component of the composition.
Lubricating oil additives, for example pour point depressants, thickeners,
viscosity
index (VI) improvers and dispersants, may be prepared using the process of the
present invention.
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Preferred polymers useful as VI improvers and/or pour point depressants com-
prise units derived from alkyl esters having at least one ethylenically
unsaturated
group. These polymers are well known in the art. Preferred polymers are obtain-
able by polymerizing, in particular, (meth)acrylates, maleates and fumarates.
The
term (meth)acrylates includes methacrylates and acrylates as well as mixtures
of
the two. These monomers are well known in the art. The alkyl residue can be
lin-
ear, cyclic or branched.
Compositions to obtain preferred copolymers comprising units derived from
alkyl
esters contain 0 to 100 wt%, preferably 0 to 90 wt%, especially 0 to 80 wt%,
more
preferably 0 to 30 wt%, more preferably 0 to 20 wt% based on the total weight
of
the monomer mixture of one or more ethylenically unsaturated ester compounds
of formula (I)
RI
R4 OR2 (I)
3 O
where R1 is hydrogen or methyl, R2 means a linear or branched alkyl residue
with
1-6 carbon atoms, R3 and R4 independently represent hydrogen or a group of the
formula -COOR', where R' means hydrogen or a alkyl group with 1-6 carbon at-
oms. In the preferred embodiment, R3 and R4 are hydrogen.
Examples of monomers according to formula (I) are mentioned above.
Furthermore, the monomer compositions to obtain preferred copolymers compris-
ing units derived from alkyl esters contain 0- 100 wt%, preferably 10-99 wt%,
es-
pecially 20-95 wt% and more preferably 30 to 85 wt% based on the total weight
of
the monomer mixture of one or more ethylenically unsaturated ester compounds
of formula (II)
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RI
R7 ORS
6 O
where R1 is hydrogen or methyl, R5 means a linear or branched alkyl residue
with
7-40, especially 10 to 30 and preferably 12 to 24 carbon atoms, R6 and R' are
in-
dependently hydrogen or a group of the formula -COOR", where R" means hy-
drogen or an alkyl group with 7 to 40, especially 10 to 30 and preferably 12
to 24
carbon atoms.
Of the ethylenically unsaturated ester compounds, the (meth)acrylates are par-
ticularly preferred over the maleates and furmarates, i.e., R3, R4, R6, R' of
formu-
las (I) and (II) represent hydrogen in particularly preferred embodiments.
In a particular aspect of the present invention, preference is given to using
mix-
tures of ethylenically unsaturated ester compounds of formula (II), and the
mix-
tures have at least one (meth)acrylate having from 7 to 15 carbon atoms in the
al-
cohol radical and at least one (meth) acrylate having from 16 to 30 carbon
atoms
in the alcohol radical. The fraction of the (meth)acrylates having from 7 to
15 car-
bon atoms in the alcohol radical is preferably in the range from 20 to 95% by
weight, based on the weight of the monomer composition for the preparation of
polymers. The fraction of the (meth)acrylates having from 16 to 30 carbon
atoms
in the alcohol radical is preferably in the range from 0.5 to 60% by weight
based
on the weight of the monomer composition for the preparation of the polymers
comprising units derived from alkyl esters. The weight ratio of the
(meth)acrylate
having from 7 to 15 carbon atoms in the alcohol radical and the (meth)acrylate
having from 16 to 30 carbon atoms in the alcohol radical is preferably in the
range
of 10:1 to 1:10, more preferably in the range of 5:1 to 1,5:1.
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Examples of monomers according to formula (II) are mentioned above.
Furthermore, the mixtures may comprise ethylenically unsaturated monomers that
can copolymerize with the ethylenically unsaturated ester compounds of formula
(I) and/or (II). Examples of these monomers are mentioned above.
In these cases, continuously variable-composition copolymers comprising single-
composition copolymers having monomeric units selected from two or more of
methyl methacrylate, butyl methacrylate, isodecyl methacrylate, lauryl-
myristyl
methacrylate, dodecyl-pentadecyl methacrylate, cetyl-eicosyl methacrylate and
cetyl-stearyl methacrylate are preferred. Preferably the continuously variable-
composition copolymers used as lubricating oil additives have an overall
average
composition of 40-90% A and 10-60% B and preferably 50-70% A and 30-50%
B , where A represents monomeric units selected from one or more of isodecyl
methacrylate (IDMA), lauryl-myristyl methacrylate (LMA) and dodecyl-pentadecyl
methacrylate (DPMA) and B represents monomeric units selected from one or
more of cetyl-eicosyl methacrylate (CEMA) and cetyl-stearyl methacrylate
(SMA).
Preferably the monomeric unit composition range of single-composition copoly-
mers in continuously variable-composition copolymers used as lubricating oil
ad-
ditives is 5 to 100%, preferably from 10 to 80%, more preferably from 20 to
50%
and most preferably from 30 to 40% for at least one of the monomeric unit com-
ponents, A or B ; for example, using the same definitions for A and B
monomeric
units as above, the continuously variable-composition copolymers may contain
10
LMA/90 SMA copolymer up to 90 LMA/10 SMA copolymer (range of 80%) or 25
LMA/75 SMA copolymer up to 75 LMA/25 SMA copolymer (range of 50%) or 30
LMA/70 SMA copolymer up to 70 LMA/30 SMA copolymer (range of 40%), with
each continuously-variable composition having an overall average composition
of
50 LMA/50 SMA. The monomeric unit composition range need not be symmetrical
around the overall average composition of the continuously-variable
composition
copolymer.
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A preferred application of this technique is the preparation of VI improver
addi-
tives that provide improved VI and low temperature performance by allowing
greater amounts of low-solubility monomers, such as methyl methacrylate, to be
used in the polymer additive. Another preferred application of this technique
is the
preparation of polymeric pour point depressant additives that provide improved
low temperature fluidity when used in a variety of petroleum base oils. In
general,
low temperature is meant to refer to temperatures below about -20 C (corre-
sponds to -4 F); fluidity at temperatures below about -25 C (corresponds to -
13
F) is of particular interest in the use of pour point depressant additives.
When the process of the present invention is used to prepare lubricating oil
addi-
tives, typical maximum [A; -AT] or [B; -BT] absolute values used during the
polym-
erization are from 5 to 100%, preferably from 10 to 80% and more preferably
from
20 to 50%, wherein A;, AT, B; and BT represent instantaneous weight percents
of
any two A and B monomers added to the reactor initially (A; and B;) and at
some
time later in the polymerization (AT and BT). For example, pour point
depressant
additives based on variable-composition copolymers prepared where the [A; -AT]
or [B; - BT] values are from 30 to 40% are preferred for use in a wide range
of base
oils.
Copolymers prepared by the process of the present invention offer wider
applica-
bility in treatment of base oils from different sources when compared to
single-
composition polymer additives or combinations of separately prepared single-
composition polymer additives. In some cases the continuously-variable composi-
tion copolymers of the present invention equal or exceed the low temperature
per-
formance of comparable single-composition polymer additives or mixtures
thereof;
in all cases the continuously-variable composition copolymers offer the
advantage
of broader applicability to different base oils without requiring the separate
prepa-
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ration and then combination of different single-composition polymers to
achieve
satisfactory performance in a variety of base oils.
Preferably, the process of this invention is used to produce continuously-
variable
composition copolymers by semi-batch methods. As used herein, semi-batch re-
fers to processes in which reactants are added to a polymerization reactor,
one or
more of which may be added over the course of the reaction, and the finished
co-
polymer is removed as the final product after polymerization has been
completed.
A batch polymerization refers to processes in which the reactants are all
added to
the reactor initially and the finished polymer is removed as the final product
after
polymerization has been completed. Among the reactor types useful in the prac-
tice of the present invention are, for example, pipe (plug-flow), recycle-loop
and
continuous-feed-stirred-tank (CFSTR) type reactors.
According to a preferred embodiment of the present process, the reaction
mixture
is intensively stirred during the addition of the second monomer composition
to
the reaction vessel. Preferably, the stirring rate in the reaction vessel is
in the
range from 10 to 1000 rpm, more preferably 50 to 500 rpm. Useful devices to
achieve a good mixing of the reaction mixture are well known in the art. E.g.
these
devices include pitched blade turbines.
Preferably, the process of the present invention can be conducted as a combina-
tion co-feed-heel process. A heel process is one where some portion of one or
more of the reactants or diluents is present in the polymerization reactor and
the
remaining reactants and diluents are then added to the reactor at some later
point. A combination of a heel and a co-feed process is one where a portion of
one or more of the reactants or diluents is present in the polymerization
reactor,
and the remainder of the one or more reactants or diluents is metered
(including
variation of individual monomer feed rates), or fed, into the reactor over a
period
of time.
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According to the process of the present invention, the monomers provided in
the
reaction vessel by the first monomer composition composes at least 50 % by
weight of all the monomers used to prepare said copolymer, preferably at least
60
% by weight of all the monomers used to prepare said copolymer and more pref-
erably at least 70 % by weight of all the monomers used to prepare said copoly-
mer. Preferably, the weight ratio of said first monomer composition to said
second
monomer composition is within the range of 20:1 to 1:1, most preferably 12:1
to
1:1
Two or more different monomer feeds can be added to the reaction vessel com-
prising the first monomer mixture. However, additional monomer feeds impart
higher efforts to control the copolymer composition and the polymerization
proc-
ess. Additionally, a higher investment is needed in order to build a plant
being
able to perform such process. Consequently, the reaction system preferably com-
prises just one feed vessel from which the second monomer composition is added
to the reaction vessel. Furthermore, the sum of the monomers of said first
mono-
mer composition and said second monomer composition preferably composes at
least 80 %, more preferably at least 95 % by weight of all the monomers used
to
prepare said copolymer. According to a preferred aspect of the present
invention
just one second monomer composition is added to the reaction vessel.
The addition rate of the second monomer composition can be either held
constant
or can be reduced or increased during the addition to the reaction vessel. In
the
preferred embodiment, the addition rate of the second monomer composition is
held constant during the addition to the reaction vessel.
According to a preferred embodiment, the addition rate of the second monomer
composition to the reaction vessel is adapted according to the conversion rate
of
the monomer composition being present in the reaction vessel. E.g. the
conversa-
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tion rate can be controlled by the initiator feed and/or by the reaction
temperature.
Preferably, the addition rate corresponds approximately to the conversion
rate.
For example, the ratio of the addition rate and the conversion rate can be
within
the range of 3:1 to 1:3, preferably 2:1 to 1:2.
The process of the present invention is applicable to preparing copolymers by
bulk or solution polymerization techniques.
The process of the present invention is particularly applicable to preparing
poly-
mers by solution polymerization. Preferably, the process of the present
invention
is applied to solution (solvent) polymerizations by mixing the selected
monomers
in the presence of a polymerization initiator, a diluent and optionally a
chain trans-
fer agent.
Generally, the temperature of the polymerization may be up to the boiling
point of
the system, for example, from about 60 to 150 C, preferably from 85 to 130 C
and more preferably from 110 to 120 C, although the polymerization can be con-
ducted under pressure if higher temperatures are used. The reaction
temperature
is either held constant or reduced at the end of the monomer feed. According
to a
preferred embodiment, the reaction temperature can be lowered by 0 C to 20 C,
more preferably 5 C to 15 C after completion of the addition of the second
mono-
mer composition. The polymerization (including monomer feed and hold times) is
run generally for about 4 to 10 hours, preferably from 2 to 3 hours, or until
the de-
sired degree of polymerization has been reached, for example until at least
90%,
preferably at least 95% and more preferably at least 97% of the
copolymerizable
monomers have been converted to copolymers. As is recognized by those skilled
in the art, the time and temperature of the reaction are dependent on the
choice of
initiator and target molecular weight and can be varied accordingly.
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When the process of the present invention is used for solvent (non-aqeuous)
poymerizations, initiators suitable for use are any of the well known free-
radical-
producing compounds such as peroxy, hydroperoxy and azo initiators, including,
for example, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, tert-butyl
peroxy-
isobutyrate, caproyl peroxide, cumene hydroperoxide, 1,1-di(tert-butylperoxy)-
3,3,5-trimethylcyclohexane, azobisisobutyronitrile and tert-butyl peroctoate
(also
known as tert-butylperoxy-2-ethylhexanoate). The total amount of initiator is
typi-
cally between 0.025 and 1 %, preferably from 0.05 to 0.5%, more preferably
from
0.1 to 0.4% and most preferably from 0.2 to 0.3%, by weight based on the total
weight of the monomers.
In the preferred embodiment of this invention, the initiator is added as a
separate
feed throughout the course of the polymerization reaction. According to that
spe-
cific embodiment, the addition of the initiator to the reaction vessel can be
per-
formed in two or more steps. Preferably, the addition rate of the initiator
can be
increased with the subsequent steps. The amount of initiator added to the
polym-
erization reaction before addition of the second monomer composition is
prefera-
bly in the range of 0.2 to 10 % by weight, more preferably 0.5 to 5 % based on
the
total amount of initiator. The amount of initiator added concurrently with the
addi-
tion of the second and subsequent monomers is preferably in the range of 20%
to
99.8% based on the total amount of initiator. More preferably, the amount
added
concurrently with the addition of the second and subsequent monomers is in the
range of 20% to 50%.
In the first and/or in the second and subsequent steps, the polymerization
initiator
can be added gradually, preferably with a constant application rate whereby
the
average application rate of the second and subsequent steps is higher than the
average application rate of the first or previous step. The ratio of the
average ap-
plication rate of the second step to the average application rate of the first
step is
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preferably more than 1.2 : 1, in particular in the range of 1.2 : 1 to 10:1,
more par-
ticular more than 1.5:1, most particular more than 2:1, especially 3:1.
Initiator addition is continued after completion of monomer feeds, with the
amount
of initiator added in the range of 20% to 80%, more preferably in the range of
40
to 70%. Alternatively, the initiator can be added as a single addition at the
com-
pletion of monomer feeds rather then added as a feed.
According to a preferred embodiment, initiator can be added to the reaction
ves-
sel as a separate continuous feed stream that starts when the reaction vessel
containing the first monomer composition reaches the desired reaction tempera-
ture.
The addition of the polymerization initiator can be carried out with or
without a sol-
vent. The addition of the polymerization initiator in solution is preferred,
in particu-
lar in form of a 3 to 25 wt% solution in at least one mineral oil.
The residual amount of polymerization initiator can be estimated in a known
man-
ner or on basis of known values as for example the decomposition rate, the tem-
perature profile during the polymerization and the addition profile.
For the addition with constant speed at a constant temperature the following
equation is approximately valid:
ISS/IE = 1 /(kd tE)
wherein the ratio ISS/IE refers to the part of polymerization initiator not
yet con-
sumed in reference to the total amount of the polymerization initiator added
in the
first step and wherein kd is the decomposition constant of the polymerization
initia-
tor and wherein tE is the addition period.
In the preferred embodiment, the addition of the polymerization initiator can
be
performed in three steps, wherein in the third step more initiator is added
than in
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the second step and more initiator is added in the second step than in the
first
step. In the preferred embodiment, the third addition step is started at the
conclu-
sion of the addition of the second monomer composition.
Alternatively, the addition of the initiator can be performed batchwise.
Further-
more, the first addition of the initiator may be performed as a batch addition
to the
first monomer composition in order to establish polymerization conditions.
After a
short time the second monomer composition is gradually added to the reaction
vessel, e.g. after 0 to 15 minutes, preferably 5 to 10 minutes. The second
mono-
mer composition may comprise polymerization initiator and, consequently, the
ad-
dition of the polymerization initiator in the second step involves the
addition of the
second monomer composition. Furthermore, the second addition of the polymeri-
zation initiator could be performed as a batch during the addition of the
second
monomer composition. E.g. the second step addition of initiator can be
performed
after 10 % by weight, preferably after 30 % by weight more preferably after 40
%
by weight of the second monomer composition has been added to the polymeriza-
tion reactor. As mentioned above, additional initiator may be added in a third
step.
The third step addition can be performed gradually or as a batch. E.g. the
third
step addition of initiator can be performed after 70 % by weight, preferably
after
90 % by weight more preferably after 100 % by weight of the second monomer
composition has been added to the polymerization reactor.
According to a preferred embodiment of the present invention, polymerization
ini-
tiator can be added to the reaction vessel after the addition of the second
mono-
mer feed has been completed. Preferably, the addition of the initiator can be
com-
pleted within a period of time of about 120 minutes, more preferably 60
minutes
after the second monomer addition has been completed and most preferably 30
minutes after the second monomer addition has been completed. The addition of
the initiator after the end of the addition of the second monomer composition
can
be performed as a batch or continuously.
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In addition to the initiator, one or more promoters may also be used. Suitable
promoters include, for example, quaternary ammonium salts such as
benzyl(hydrogenated-tallow)-dimethylammonium chloride and amines. Preferably
the promoters are soluble in hydrocarbons. When used, these promoters are
present at levels from about 1 % to 50%, preferably from about 5% to 25%,
based
on total weight of initiator.
Chain 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 mercaptan (also known as dodecyl mercaptan, DDM),
and the concentration of chain transfer agent used is from zero to about 2%,
pref-
erably from zero to 1 %, by weight.
If used, the chain transfer agent can be added during the polymerization
reaction
and/or before the start of the polymerization reaction. Preferably, the first
mono-
mer composition comprises at least 0.05% by weight, more preferably at least
0.1 % by weight of the chain transfer agent and/or the second monomer composi-
tion comprises at least 0.05% by weight, more preferably at least 0.1 % by
weight
of the chain transfer agent. According to a preferred embodiment, the first
mono-
mer composition and the second comprises at least one chain transfer agent.
When the polymerization is conducted as a solution polymerization using a sol-
vent other than water, the reaction may be conducted at up to about 100%
(where
the polymer formed acts as its own solvent) or up to about 70%, preferably
from
80 to 95%, by weight of polymerizable monomers based on the total reaction mix-
ture. The solvents, if used, can be introduced into the reaction vessel as a
heel
charge, or can be fed into the reactor either as a separate feed stream or as
a
diluent for one of the other components being fed into the reactor.
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Diluents may be added to the monomer mix or they may be added to the reactor
along with the monomer feed. Diluents may also be used to provide a solvent
heel, preferably non-reactive, for the polymerization. Preferably, materials
se-
lected as diluents should be substantially non-reactive towards the initiators
or in-
termediates in the polymerization to minimize side reactions such as chain
trans-
fer and the like. The diluent may also be any polymeric material which acts as
a
solvent and is otherwise compatible with the monomers and polymerization ingre-
dients being used.
Among the diluents suitable for use in the process of the present invention
for
non-aqueous solution polymerizations are aromatic hydrocarbons (such as ben-
zene, toluene, xylene and aromatic naphthas), chlorinated hydrocarbons (such
as
ethylene dichloride, chlorobenzene and dichlorobenzene), esters (such as ethyl
propionate or butyl acetate), (C6 -C20)aliphatic hydrocarbons (such as
cyclohex-
ane, heptane and octane), petroleum base oils (such as paraffinic and
naphthenic
oils) or synthetic base oils (such as olefin copolymer (OCP) lubricating oils,
for
example poly(ethylene-propylene) or poly(isobutylene)). When the concentrate
is
directly blended into a lubricating base oil, the more preferred diluent is
any min-
eral oil, such as 100 to 150 neutral oil (100 N or 150 N oil), which is
compatible
with the final lubricating base oil.
In the preparation of lubricating oil additive polymers, the resultant polymer
solu-
tion, after the polymerization, generally has a polymer content of about 50 to
95%
by weight. The polymer can be isolated and used directly in lubricating oil
formu-
lations or the polymer-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. The preferred concentration of
polymer in
the concentrate is from 30 to 70% by weight. When a polymer prepared by the
process of the present invention is added to base oil fluids, whether it is
added as
pure polymer or as concentrate, the final concentration of the polymer in the
for-
mulated fluid is typically from 0.05 to 20%, preferably from 0.2 to 15% and
more
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preferably from 2 to 10%, depending on the specific use application
requirements.
For example, when the continuously variable-composition copolymers are used to
maintain low temperature fluidity in lubricating oils, for example as pour
point de-
pressants, the final concentration of the continuously variable-composition co-
polymer in the formulated fluid is typically from 0.05 to 3%, preferably from
0.1 to
2% and more preferably from 0.1 to 1%; when the continuously variable-
composition copolymers are used as VI improvers in lubricating oils, the final
con-
centration in the formulated fluid is typically from 1 to 6% and preferably
from 2 to
5%; and when the continuously variable-composition copolymers are used as hy-
draulic fluid additives, the final concentration in the formulated fluid is
typically
from 5 to 15% and preferably from 3 to 10%.
The continuously variable composition copolymer is soluble in lubricating oil.
Lu-
bricating oils are well known in the art. Usually, these oils comprise
petroleum
base oils (such as paraffinic and naphthenic oils) or synthetic base oils as
men-
tioned above. Lubricating oils are also used as hydraulic fluids. As used
herein
the term "soluble" means that one fluid phase is formed with the lubricating
oil af-
ter addition of an effective amount of the present copolymers as mentioned
above.
Weight-average molecular weights of copolymers useful as lubricating oil addi-
tives may be from 10,000 to 1,000,000. As the weight-average molecular weights
of the polymers increase, they become more efficient thickeners; however, they
can undergo mechanical degradation in particular applications and for this rea-
son, polymer additives with Mw above about 500,000 are not suitable because
they tend to undergo "thinning" due to molecular weight degradation resulting
in
loss of effectiveness as thickeners at the higher use temperatures (for
example, at
100 C.). Thus, the desired Mw is ultimately governed by thickening
efficiency,
cost and the type of application. In general, polymeric pour point depressant
addi-
tives of the present invention have Mw from about 30,000 to about 700,000 (as
determined by gel permeation chromatography (GPC), using
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poly(alkylmethacrylate) standards); preferably, Mw is in the range from 60,000
to
350,000 in order to satisfy the particular use as pour point depressants.
Weight-
average molecular weights from 70,000 up to 300,000 are preferred.
The polydispersity index of the polymers prepared by the process of the
present
invention may be from 1 to about 15, preferably from 1.5 to about 4. The
polydis-
persity index (Mw /Mn, as measured by GPC, where Mn is number-average mo-
lecular weight) is a measure of the narrowness of the molecular weight
distribution
with higher values representing increasingly broader distributions. It is
preferred
that the molecular weight distribution be as narrow as possible for polymers
used
as VI improvers in crankcase and hydraulic fluid applications, but this is
generally
limited by the method of manufacture. Some approaches to providing narrow mo-
lecular weight distributions (low Mw /Mn) include, for example, one or more of
the
following methods: continuous-feed-stirred-tank-reactor (CFSTR); low-
conversion
polymerization; control of temperature or initiator/monomer ratio (such as dis-
closed in EP 561078 to achieve a constant degree of polymerization) during po-
lymerization; and mechanical shearing, for example homogenization, of the poly-
mer.
Those skilled in the art will recognize that the molecular weights set forth
through-
out this specification are relative to the methods by which they are
determined.
For example, molecular weights determined by GPC and molecular weights calcu-
lated 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. A VI improving
addi-
tive with good shear stability (low SSI value, see below) is typically used at
higher
initial concentrations relative to another additive having reduced shear
stability
(high SSI value) to obtain the same target thickening effect in a treated
fluid at
high temperatures; the additive having good shear stability may, however, pro-
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duce unacceptable thickening at low temperatures due to the higher use concen-
trations.
Therefore, polymer composition, molecular weight and shear stability of pour
point
depressant and VI improving additives used to treat different fluids must be
se-
lected to achieve a balance of properties in order to satisfy both high and
low tem-
peratures performance requirements.
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
vis-
cosity due to mechanical shearing and can be determined, for example, by meas-
uring sonic shear stability for a given amount of time according to ASTM D-
2603-
91 (published by the American Society for Testing and Materials). Depending on
the end use application of the lubricating oil, the viscosity is measured
before and
after shearing for specified time periods to determine the SSI value. In
general,
higher molecular weight polymers undergo the greatest relative reduction in mo-
lecular weight when subjected to high shear conditions and, therefore, these
higher molecular weight polymers also exhibit the largest SSI values.
Therefore,
when comparing the shear stabilities of polymers, good shear stability is
associ-
ated with the lower SSI values and reduced shear stability with the higher SSI
val-
ues.
The SSI range for alkyl (meth)acrylate polymers useful as lubricating oil
additives
(for example: VI improvers, thickeners, pour point depressants, dispersants)
pre-
pared by the process of this invention is from about zero to about 60%,
preferably
from 1 to 40% and more preferably from 5 to 30% and will vary depending upon
the end use application; values for SSI are usually expressed as whole
numbers,
although the value is a percentage. The desired SSI for a polymer can be
achieved by either varying synthesis reaction conditions or by mechanically
shearing the known molecular weight product polymer to the desired value.
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Representative of the types of shear stability that are observed for
conventional
lubricating oil additives of different Mw are the following: conventional
poly(methacrylate) additives having Mw of 130,000, 490,000 and 880,000, re-
spectively, would have SSI values (210 F) 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 (210 F) were 0, 35 and 50%, respectively; and based on a 100 hour ASTM
D-2882-90 pump test for hydraulic fluids, the SSI values (100 F) 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, Tex., Jun. 3-5, 1975, Society of Automotive Engineers).
Pumpability of an oil at low temperatures, as measured by the mini-rotary
viscometer (MRV), relates to viscosity under low shear conditions at engine
startup. Since the MRV test is a measure of pumpability, the engine oil must
be
fluid enough so that it can be pumped to all engine parts after engine startup
to
provide adequate lubrication. ASTM D-4684-89 deals with viscosity measurement
in the temperature range of -10 to -30 C. and describes the TP-1 MRV test.
SAE
J300 Engine Oil Viscosity Classification (December 1995) allows a maximum of
pascal*seconds (pa*sec) or 300 poise at -30 C for SAE 5W-30 oil using the
ASTM D-4684-89 test procedure. Another aspect of low temperature performance
measured by the TP-1 MRV test is yield stress (recorded in pascals); the
target
value for yield stress is "zero" pascals, although any value less than 35
pascals
25 (limit of sensitivity of equipment) is recorded as "zero" yield stress.
Yield stress
values greater than 35 pascals signify increasing degrees of less desirable
performance.
The invention is illustrated in more detail below by examples and comparison
ex-
30 amples, without intending to limit the invention to these examples.
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Example 1
A reaction mixture is prepared by blending 465 parts LMA, 438 parts SMA, and
3.3 parts DDM. The reaction mixture is heated to 120 C and a free radical
initiator
solution of 3.8 parts t-butyl peroctoate (50% in odorless mineral spirits) and
19.3
parts 100N polymerization oil is added over 165 minutes. Ten percent of this
free
radical initiator solution is added in the first hour, followed by 20% in the
second
hour, and the remainder in the final 0.75 hours. The monomer addition mixture
consisting of 70 parts LMA and 0.26 parts DDM is added at a constant rate over
1.92 hours, with the addition starting 5 minutes after the start of the
initiator solu-
tion addition. The reaction temperature is decreased to 105 C at the end of
the
addition of the monomer mixture. The reaction mixture is held one hour after
com-
pletion of the initiator addition, than diluted with 1467.5 parts of 100N oil.
The
composition of materials formed starts at about 52% LMA, 48% SMA and ends at
about 59% LMA,41 % SMA. The product before the dilution step contained 94.1 %
polymer solids, which represented a 99.0% conversion of monomers to polymer.
The polymer produced has an average molecular weight of about 124,000 and a
polydispersity of about 3.35.
The obtained continuously variable composition copolymers are evaluated by us-
ing different base oils. The results achieved are shown in Table 1.
Comparative Example 1
Monomer mixture "A" is prepared by blending 535 parts LMA, 4.22 parts t-butyl
peroctoate (50% in odorless mineral spirits), and 0.95 parts n-DDM. Monomer
mixture "B" is prepared by blending 438 parts SMA, 3.38 parts t-butyl
peroctoate
(50% in odorless mineral spirits), and 0.76 parts n-DDM. 143.4 parts of 100N
po-
lymerization oil and 0.95 parts t-butyl peroctoate (50% in odorless mineral
spirits)
is added to a reaction vessel and heated to 120 C. Monomer mixture "A" and
monomer mixture "B" is fed to the reactor over 90 minutes at rates designed to
provide a starting monomer ratio of 52 percent LMA and an ending monomer ratio
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of 59 percent LMA. At the end of the monomer feed, the temperature is
decreased
to 110 C and 2.91 parts t-butyl peroctoate (50% in odorless mineral spirits)
is fed
at a constant rate over 30 minutes. The reaction mixture is held 30 minutes
after
completion of the initiator addition, than diluted with 1336 parts of 100N
oil.
The obtained continuously variable composition copolymers are evaluated by us-
ing different base oils. The results achieved are shown in Table 1 and Table
2.
Table 1: Application Results
Formulation 1 Formulation 2 Formulation 3 Formulation 4
PPD Single Single Single Single
Process Feed Control Feed Control Feed Control Feed Control
SAE
GRADE 5W-30 5W-30 5W-30 5W-30 5W-30 5W-30 10W-? 10w-?
TP1 @ -35 -35 -35 -35 -35 -35 -30 -30
Ys 0 0 0 0 0 0 0 0
Viscosity 248 234 156 161 158 159 193 170
TP1 @ -40 -40 -40 -40 -40 -40 -35 -35
Ys 0 0 0 0 0 0 0 0
Viscosity 860 798 402 452 449 451 525 447
Example 2
A reaction mixture is prepared by blending 530 parts LMA, 582 parts CEMA, and
4.1 parts n-DDM. The reaction mixture is heated to 120 C and a free radical
initia-
tor solution of 5.2 parts t-butyl peroctoate (50% in odorless mineral spirits)
and
30.3 parts 1 00N polymerization oil is added over 100 minutes. Fifteen percent
of
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this free radical initiator solution is added in the first 30 minutes,
followed by 25%
in the next 40 minutes, and the remainder in the final 30 minutes. The monomer
addition mixture consisting of 216 parts LMA and 0.8 parts n-DDM is added at a
constant rate over 65 minutes, with the addition starting 5 minutes after the
start
of the initiator solution addition. The reaction temperature is decreased to
105 C
at the end of the addition of the monomer mixture. The reaction mixture is
held
one hour after completion of the initiator addition, than diluted with 2006.2
parts of
100N oil. The composition of materials formed starts at about 48% LMA, 52%
CEMA and ends at about 65% LMA,15% CEMA. The product before the dilution
step contained 94.6% polymer solids, which represented a 99.6% conversion of
monomers to polymer. The polymer produced had an average molecular weight
of about 133,000 and a polydispersity of about 3Ø
Example 3
A reaction mixture is prepared by blending 544.8 parts LMA, 230.3 parts MMA,
107.3 parts 100N polymerization oil and 5.14 parts n-DDM. The reaction mixture
is heated to 110 C and a free radical initiator solution of 4.6 parts t-butyl
peroc-
toate (50% in odorless mineral spirits) and 69 parts 100N polymerization oil
is
added over 165 minutes. Ten percent of this free radical initiator solution is
added
in the first hour, followed by 20% in the second hour, and the remainder in
the fi-
nal 45 minutes. The monomer addition mixture consisting of 389.2 parts LMA and
2.6 parts n-DDM is added at a constant rate over 115 minutes, with the
addition
starting 5 minutes after the start of the initiator solution addition. The
reaction
temperature is decreased to 100 C at the end of the addition of the monomer
mix-
ture. The reaction mixture is held 30 minutes after completion of the
initiator addi-
tion, than diluted with 245.6 parts of 100N oil. The composition of materials
formed starts at about 70% LMA, 30% MMA and ends at about 90% LMA,10%
MMA. A 99.6% conversion of monomers to polymer had been achieved.
Example 4
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A reaction mixture is prepared by blending 522 parts LMA, 410 parts SMA, and
3.4 parts DDM. The reaction mixture is heated to 120 C and a free radical
initiator
solution of 5.20 parts t-butyl peroctoate (50% in odorless mineral spirits)
and
27.61 parts 100N polymerization oil is added over 120 minutes. Fifteen percent
of
this free radical initiator solution is added in the first hour, followed by
25% in the
next half hour, and the remainder in the final half hour. The monomer addition
mixture consisting of 270 parts LMA, 129 parts of SMA and 1.46 parts DDM is
added at a constant rate over 1.5 hours, with the addition starting at the
start of
the initiator solution addition. The reaction temperature is decreased to 105
C at
the end of the addition of the monomer mixture. The reaction mixture is held
one
hour after completion of the initiator addition, than diluted with 2052.6
parts of
100N oil. The composition of materials formed starts at about 56.5% LMA, 43.5%
SMA and ends at about 63.5% LMA, 36.5% SMA. The product before the dilution
step contained 94.1 % polymer solids, which represented a 99.0% conversion of
monomers to polymer. The polymer produced has an average molecular weight
of about 101,000 and a polydispersity of about 2.27.
The obtained continuously variable composition copolymers are evaluated by us-
ing different base oils. The results achieved are shown in Table 2.
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Table 2: Application Results
Formulation 1 Formulation 2 Formulation 3
PPD Single Single Single
Process Feed Control Feed Control Feed Control
SAE GRADE 5W-30 5W-30 10W-40 10W-40 5W-30 5W-30
TP1 @ -35 -35 -30 -30 -35 -35
Ys 0 0 0 0 0 0
Viscosity 19,400 18,400 29,800 30,500 19,100 18,300
ASTM D5133
Gel Index 6.0 6.1 4.7 4.3 7.7 9.1
Viscosity @-300C 20,456 21,008 31,242 35,248 19,783 25,404
Example 5
A reaction mixture is prepared by blending 447 parts LMA, 352 parts SMA, and
2.9 parts DDM. The reaction mixture is heated to 120 C. A monomer addition
mixture consisting of 344.5 parts LMA, 187 parts of SMA, 1.95 parts DDM and
5.2
parts t-butyl peroctoate (50% in odorless mineral spirits) is added at a
constant
rate over 1.5 hours. The reaction temperature is decreased to 105 C at the end
of
the addition of the monomer mixture and an initiator solution consisting of
2.6
parts t-butyl peroctoate (50% in odorless mineral spirits) and 25 parts 100N
po-
lymerization oil is fed at a constant rate over 30 minutes. The reaction
mixture is
held one hour after completion of the initiator addition, than diluted with
2052.6
parts of 100N oil. The composition of materials formed starts at about 56.5%
LMA,
43.5% SMA and ends at about 63.5% LMA, 36.5% SMA. The polymer produced
has an average molecular weight of about 105,000 and a polydispersity of about
2.35.
