Note: Descriptions are shown in the official language in which they were submitted.
12~5~
.
DISPEl:~SAi~T--VISCOSITY INDEX IMPROVER PRODUCT
This invention is directed to an oil-soluble product
useful in lubricating oil compositions. ~lore particularly, this
invention is directed to a star-shaped polymer having the proper-
ties of both a viscosity index improver and a dispersant, the
preparation thereof and lubricating oil compositions containing it.
The newer engines place increased demands on the lubri-
cants to be employed. In the past a number of different additives
have been added to lubricating oils to improve such properties as
viscosity index and dispersancy. One such additive added to
lubricating oils to improve viscosity index is a two-block copoly-
mer having the general configuration A-B where A is styrene and s
is hydrogenated isoprene. See generally United States Patent Nos.
3,763,044 and 3,772,196. A VI improver having greatly improved
mechanical shear stability is the selectively hydrogenated star-
shaped polymer disclosed in United States Patent No~ 4,116,917.
Significant reductions in cost can be made by employing
a single additive that improves a number of lubricant properties.
For example, in United States Patent No. 4,141,847 a selectively
hydrogenated star-shaped polymer is reacted first with an alpha-
beta carboxylic acid, anhydride or ester, and then the product is
reacted with an amine to form a dispersant-VI improver. Likewise,
in United States Patent No. 4,077,893 a similar product is obtained
where an alkane polyol reactant is employed in place of the amine
reactant to form a dispersant-VI improver. Still further, in the
copending United States patent application 4,358,565 a hydrogenated
~ I" '' ' ''!'
p,.. '` 4~ ~
:lZ~55~
- la -
star-shaped polymer is reacted with a nitrogen containing polymeri-
zable organic polar compound to form a dispersant-VI improver.
The processes to form the above three products all have certain
shortcomings. In each of the above-described patents, the syn-
thesis process involved an additional step whereby the star-
shaped polymer is subjected to either free radical polymerization
initiators, such as, tert-butyl hydroperoxide and tert-butyl ben-
zoate or a high temperature condensation reaction between an ~-~un-
3 20SS9V
-- 2 --
saturated carboxylic acid or derivative and the residual olefinbonds in the star-polymer. The acidic derivatized site would then
be reacted with an amine ~r alkane polyol. The high ~emperatures
required for the free radical process (140~C) and condensation
processes (180-250C) add higher energy requirements for their
manufacture and the additional reaction time as well as high
temperatures increase the likelyhood of unwanted side-reactions
such as cross-linking and chain-sciss~on of the polymer. In each
case the addition of a polar molecule, and more specifically a
nitrogen-based molecule to the star-polymer backbone allows for
the attainment of dispersant properties. Further process difficul-
ties are encountered in controlling the degree of graftlng and
reproduceability of the functionalization reaction.
A new lube additive has been found that has significantly
improved property advantages over the prior art additives.
The present invention is directed to an oil-soluble, star-
shaped product having the properties of both a viscosity index-
improver and a dispe~sant, said oil soluble product comprising:
(a) a poly(polyalkenyl aromatic)nucleus;
(b) at least three hydrogenated polymeric arms linked to said
nucleus, said hydrogenated polymeric arms bein~ selected from
the group consisting o~:
(i) hydrogenated homopolymers and hydrogenated copolymers of
con~ugated dienes;
(ii) hydrogenated copolymers of conjugated dienes and mono-
alkenyl arenes; and
(iii)mixtures thereof; and wherein at least about 80% of the
aliphatic unsaturation of the polymeric arms has been
reduced by hydrogenation while preferably less than 20%
of the aromatic unsaturation has been reduced, and
(c) a~ least one polymerized nitrogen containing polar compound
arm linked to said nucleus.
The dispersant-VI improvers of the present invention possess
excellent viscosity improving properties, oxidative stability,
mechanical shear stability and dispersancy. The advantages of the
1~5590
-- 3 --
above-described process include lower functionalization tempera-
tures, better control of the process and the degree of function-
alization, short reaction times, and less polymer degradation such
as cross-linking and chain scission. In essence, this process
involves terminating the poly(polyalkenyl aromatic)nucleus with a
suitable polar compound. This added step is a simple addition to
the process of forming the said star-polymers and requires no
inc}eased temperatures, extra catalysts or long reaction times to
affect the functionalization. Likewise, control over the degree of
added polar compound which becomes chemically bonded to the poly
(polyalkenyl aromatic)nucleus can be achieved by adjusting the
molar ratio of polar compound to organo lithium compound used to
polymerize the arms of the star-polymer.
The process for preparing this product comprises:
(a) solution polymerizing one or more conjugated diene and
optionally one or more monoalkenyl arene monomers under
polymerization conditions with an organolithium compound,
forming living polymeric arms;
(b) contacting said living polymeric arms with a polyalkenyl
aromatic coupling agent forming a coupled polymer having a
poly(polyalkenyl aromatic)nucleus and attached polymeric
arms;
(c) contacting said coupled polymer with a nitrogen containing
polar compound monomer attaching poly(nitrogen containing
polar compound)arms to said nucleus, and
td) reducing by hydrogenation at least 80% of tbe aliphatic
unsaturation of the polymeric arms while preferably reducing
les~ than 20% of the aromatic unsaturation.
A~ is well-known, living polymer~ may be prepared by anionic
solution polymerization of conjugated dienes and, optionally,
monoalkenyl arene compounds in the presence of an alkali metal or
an alkali-metal hydrocarbon, e.g., sodium naphthalene, as anionic
initiator. The preferred initiator is lithium or a monolithium
hydrocarbon. Secondary-butyllithium is the preferred initiator.
The initiators may be added ~o the polymerization mixture in two
120~5~
or more stages optionally together with additional monomer. The
living polymers are olefinically and, optionally, aromatically
unsaturated.
The living polymers obtained by reaction step (a), which are
linear unsaturated living polymers, are prepared from one or more
conjugated dienes, e.g., C4 to Cl2 conjugated dienes and, op-
tionally, one or more monoalkenyl arene compounds.
Preferred dienes are, butadiene and/or isoprene. Preferred
monoalkenyl arene compounds are the monovinyl aromatic compounds
such as styrene, as well as the alkylated derivatives thereof. If
a monoalkenyl arene compound is used in the preparation of the
living polymers it is preferred that the amount thereof be below
about 50% by weight, preferably about 3% to about 50%.
The living polymers may be living homopolymers or living
copolymers. E.g. the living homopolymers may be represented by the
formula A-M, wherein M is an ionic group, e.g., lithium, and A is
polybutadiene or polyisoprene. Living polymers of isoprene are the
preferred living homopolymers.
The living copolymers may be living block copolymers, living
random copolymers or living tapered copolymers.
The solvents in which the living polymer6 are formed are
inert liquid solvents such as hydrocarbons, e.g., aliphatic
hdyrocarbons, such as pentane, hexane, heptane octane, 2-ethyl-
hexane, nonane, decane, cyclohexane 9 methylcyclohexane or aromatic
hydrocarbons, e.g., benzene, toluene, ethylbenzene, the xylenes,
diethylbenzenes, propylbenzenes. Cyclohexane is preferred. Mix-
tures of hydrocarbons, such as a lubricating oil~ may also be
used.
The temperature at which the polymerization i6 carried out
30 may vary between wide limits such as from -75C to 150C, pre-
ferably from 20C to 80C. The reaction is suitably carried out in
an inert atmosphere such as nitrogen and may be carried out under
pressure, e.g., a presfiure of from 0.5 to 10 bars.
~2~5~3~
The concentration of the initiator used to prepare the living
polymer may also vary between wide limits and is determined by the
desired molecular weight of the living polymer.
The molecular weight of the living polymers prepared in
reaction step (a) may vary between wide limits. Suitable number
average molecular weights are from 5,000 to 150,000 with number
average molecular weights of from 15,000 to lO0,000 being pre-
ferred. Consequently, the number average molecular weight of the
hydrogenated polymers chains of the final star-shaped polymer may
l0 also vary between these limits.
The living polymers produced in reaction step (a) are then
reacted, in reaction step (b), with a polyalkenyl coupling agent.
Polyalkenyl coupling agents capable of forming star-shaped po-
lymers are known. See generally U.S. Patent No. 3,985,830, Ca-
nadian Patent No. 716,645, and British Patent No. 1,025,295. Theyare usually compounds having at least two non-conjugated alkenyl
groups. Such groups are usually attached to the same or different
electron-with-drawing groups, e.g., an aromatic nucleus. Such~
compounds have the property that at least two of the alkenyl
groups are capable of independent reaction w~th different living
polymers and in this respect are different from conventional
conjugated diene polymerizable monomers such as butadiene, i-
soprene, etc. Pure or technical grade polyalkenyl coupling agents
may be used. The preferred coupling agents are the polyalkenyl
aromatic compounds and the most pref~rred are the polyvinyl
aromatic compounds. Examples of such compounds include those
aromatic compounds, e.g., benzene, toluene, xylene, anthracene,
naphthalene and durene which are substituted by at least two
alkenyl groups preferably directly attached thereto. The preferred
compounds are represented by the formula: A-4CHu~_CH2)x wherein h
i6 an optionally substituted aromatic nucleus and x i8 an lnteger
of at least 2. Divinyl benzene, in particular metadivinyl benzene,
is the most preferred aromatic compound. Pure or technical grade
divinylbenzene (containing various amounts of other monomers,
e.g., styrene and ethyl styrene) may be used. The coupling agents
3 2(~5S90
-- 6 --
may be used in admixture with small amounts of added monomers
which increase the size of the nucleus, e.g., styrene or alkylated
styrene. In this case, the nucleus may be described as a poly-
(dialkenyl) coupling agent/monoalkenyl aromatic compound)nucleus,
e.g., a poly(divinylbenzene/monoalkenyl aromatic compound)-
nucleus. From the above it will be clear that the term divinyl-
benzene when used to describe the nucleus means either purified or
technical grade divinyl benzene.
The polyalkenyl coupling agent should be added to the living
polymer after the polymerization of the monomers is substantially
complete, i.e., the agent should only be added after substantially
all of the diene and monoalkenyl arene monomer has been converted
to living polymers.
The amount of polyalkenyl coupling agent added may vary
between wide limits but preferably at least 0.5 mole is used per
mole of unsaturated living polymer. Amounts of from 1 to 15 moles,
preferably from 1.5 to 5 moles are preferred. The amount, which
may be added in two or more stages, is usually such so as to
convert at least 80 or 85%w of the living polymers into star-
shaped polymers.
The reaction step (b) may be carried out in the same solventsas for reaction step (a). A list of suitable solvents is given
above. In reaction step (b) the temperature may also vary between
wide limits, e.g., from 0 to 150C, preferably from 20 to 120C.
The reaction may also take place in an inert atmosphere, e.g.,
nitrogen and under pressure, e.g., a pressure of from 0.5 to 10
bars.
The star-shaped polymers prepared in reaction step (b) are
characterized by having a dense centre or nucleus of cross-linked
poly(polyalkenyl coupling agent) and a number of arms of sub-
stantially linear unsaturated polymers extending outwardly there-
from. The number of arms may vary considerably but is typically
between 3 and 25, preferably from about 7 to about 15. Star-
shaped homopolymers may be represented by the formula A-x--~A)
and star-shaped copolymers may be represented by the formula
lZOS~
A-B-x (s-A)n wherein n is an integer, usually between 2 and 24
and x is the poly(polyalkenyl coupling agent)nucleus. From the
above it can be seen that x is preferably a poly(polyvinyl aro-
matic coupling agent)nucleus and more preferably a poly(divinyl-
benzene)nucleus. As stated above it is believed that the nucleiare cross-linked. It has been found that the greater number of arms employed in
the instant invention significantly improve both the thickening
efficiency and the shear stability of the polymer since it is then
possible to prepare a VI-improver having a high molecular weight
(resulting in increased thickening efficiency) wlthout the ne-
cessity of excessively long arms (resulting in improved shear
stability).
In step (C), the star-shaped polymer ls contacted with a
nitrogen-containing polar compound monomer, resulting in the
attachment of at least one polymer arm directly to the poly(poly-
vinyl aromatic)nucleus. The nitrogen containing polar compound is
preferably selected from the group consisting of 2-vinylpyridine
and 4-vinylpyridine, with 2-vinylpyridine being most preferred.
However, other polymerizable nitrogen-bearing compounds are also
contemplated in the present invention, including, by way of
example: 2-methyl, 5-vinyl pyridine; acrylamide; methacrylamides;
N-alkyl acrylamides; N,N-dialkyl acrylamides; N,N- dialkylmethacryl-
amides, where the alkyl group contains from one to seven carbon
atoms. Other polymerizable nitrogen-bearing compounds are:
N-vinyl imidazole and N-viny~ carbazole; s-caprolactam; N-vinyl-
oxazolidone; N-vinylcaprolactam; N-vinylthiocaprolactam; and
N-vinyl-pyrrolidone. Non-polymerizable nitrogen heterocycles can
also be added with the polymerizable nitrogen-containing polar
compound to give the desired functionality including: piperidine,
pyrrolidine, morpholine, pyridine, aziridine, pyrrole, indole,
pyridazine, quinoline and isoquinoline, pyridazine, pyrimidine,
pyrazine, and derivatives and poly-pyridines having less than 20
pyridyl groups such as 2,2'-bipyridine and tripyridine, etc.
1205S90
-- 8 --
In the interests of simplicity, the remainder of the spe-
cification shall refer to vinylpyridine instead of nitrogen-
containing polar compound.
After contacting the star-shaped polymer with the vinyl-
pyridine monomer, the resulting star-shaped copolymer contains
about 0.1 to about 10 per cent by weight vinylpyridine, preferably
about 0.1 to about 5.0 per cent by weight. The number of poly(vinyl-
pyridine)arms is typically between one and about 10, preferably
between one and about 5. Accordingly, the molecular weight of the
]O poly(vinylpyridine) arms is between about 105 and about 10,000,
preferably between about 105 and about 1000.
The addition of the polar compound, preferably 2-vinylpyrl-
dine, to the poly(polyalkenyl aromatic)nucleus occurs at tem-
peratures between -78C and +80C, preferably between 25C and
60C.
The molecular weights of the star-shaped polymer to be
hydrogenated may vary between relatively wide limits. However, an
important aspect of the presen~ invention is that polymers posses-
sing good shear stability may be produced even though the polymers
have very high molecular weights. It is possible to produce star
polymers having peak molecular weights between about 25,000 and
about 1,250,000. Preferred molecular weights are 100,000 to
500,000. These peak molecular weights are determined by gel
permeation chromotography (GPC) on a polyætyrene scale.
In step (d), the star-shaped polymers are hydrogenated by any
suitable technique. Suitably at least 80%, preferably 90 to abou~
98% of the original olPfinic unsaturation is hydrogenated. If the
star-shaped polymer is partly derived from a monoalkenyl arene
compound, then the amount of aromatic unsaturation which i6
hydrogenated, if any, will depend on the hydrogenation conditions
used. However, preferably less than 20%, more preferably less than
5% of æuch aromatic unsaturation is hydrogenated. If the poly(poly-
alkenyl coupling agent)nucleus is a poly~polyalkenyl aromatic
coupling agent)nucleus, then the aromatic unsaturation of the
nucleus may or may not be hydrogenated again depending upon
~0559~
the hydrogenation conditions used. The molecular weights of the
hydrogenated star-shaped polymers correspond to those of the
unhydrogenated star-shaped polymers.
The hydrogenation of the olefinic unsaturation is important
5 with the regard to the thermal and oxidative stability of the
product. This hydrogenation may be carried out in any desired way.
The hydrogenation of the star-shaped polymer is very suitably
conducted in solution in a solvent which is inert during the
hydrogenation reaction. Saturated hydrocarbons and mixtures of
10 saturated hydrocarbons are very suitable and it is of advantage to
carry out ~he hydrogenation in the same solvent in which the
polymerization has been effected.
A much preferred hydrogenation process is the selective
hydrogenation process shown in U.S. Patent No. 3,595,942. In that
15 process, hydrogenation is conducted, preferably in the same
solvent in which the polymer was prepared, utiliæing a catalyst
comprising the reaction product of an aluminium alkyl and a nickel
or cobalt carboxylate or alkoxide. A favoured catalyst is the
reaction product formed from triethyl aluminium and nickel octoate.
Another suitable process is a stoichometric hydrogenation
process wherein the polymer is contacted with a hydrazine or
p-toluenesulphonylhydrazide reactant forming N2H2, which reduces
the polymer by hydrogenation.
The advantage of the p-toluenesulphonylhydrazide and hydrazine
25 hydrogenation technique iB the ability to selectively reduce
olefin unsaturation within the block copolymers without excessive
degradation (chain-sci~sion, cross-linking) of the polymer chain.
Likewise, hydrogenation by this technique is mild and can be
achieved in the presence of various functional groups. Specifi-
30 cally the unsatureated portion of the polymer chains containingprlmary, secGndary or tertiflry amines can be reduced to at least
about 80%. Other functional groups which are rather inert toward
the dilmide reduction process are double-bonds which possess a
polar character such as: (-C--N,~C=N-,~C=O). Hence, the ma~or
35 advantage of the diimide reduction procedure is the
1205590
-- 10 --
selectivity, allowing for the reduction of the olefinic sites
within the block-polymer chain, while leaving other polar func-
tional groups intact. Preferred solvents are cyclohexane, hexane,
benzene, toluene, meta-, ortho- and para-xylenes or mixtures
5 thereof. Most preferably, xylenes are used as the hydrogenation
solvent.
Without wishing to be bound to a particular theory, it is
considered that in this stoichiometric hydrogenation, the reactant
thermally decomposes, resulting in the formation of a diimide
10 which serves as the actual hydrogenating agent. Next, the diimide
quickly undergoes a concerted cis-addition to the polymer alipha-
tic do~ble bonds affecting the hydrogenation, while releasing
nitrogen as the gaseous by-product. The reactants employed herein
include p-toluenesulphonylhydrazide (PTSH) and hydrazine, with
15 PTSH being preferred.
The mechanism of the hydrogenation step can be envisioned as
follows, with PTSH as the reactant:
(1) CH3 ~ S02NH-NH2 ~ uxC 3 ~ S02H + ~¦¦
Xylene 135C NH
Diimide
H ~ HC-CH3
+ 11 3 N (~)~ +
N
H
~20SS90
The temperature during the reactant decomposition stage is
e.g. between 50C and 150C, preferably between 80C and 135C.
The molar ratio of PTSH or hydrazine reactant to conjugated diene
units (aliphatic unsaturation bonds) is typically between 5:1 and
1:1, preferably between 3:1 and 1:1.
The hydrogenated star-shaped polymer is then recovered in
solid form from the solvent in which it is hydrogenated by any
convenient technique such as by evaporation of the solvent.
Alternatively, an oil, e.g., a lubricating oil, may be added to
the solution and the solvent stripped off from the mixture so
formed to produce concentrates. Easily handleable concentrates are
produced even when the amount of hydrogenated star-shaped polymer
therein exceeds 10%w. Suitable concentrates contain from 10 to
25%w of the hydrogenated star-shaped polymer.
The reaction product of this invention can be incorporated $n
lubricating oil compositions, e.g., automotive crankcase oils, in
concentrations within the range of about 0.1 to about 15, pre-
ferably about 0.1 to 3, /OW based on the weight of the total
compositions. The lubricating oils to which the additives of the
invention can be added include not only mineral lubricating oils,
but synthetic oils also. Syn~hetic hydrocarbon lubricating oils
may also be employed, as well as non-hydrocarbon synthetic oils
including dibasic acid esters such as di-2-ethyl hexyl sebacate,
carbonate esters, phosphate esters, halogenated hydrocarbons,
polygilicones, polyglycols, glycol esters such as C13 oxo acid
diesters of tetraethylene glycol, etc. When used in gasoline or
fuel oil, e.g., diesel fuel, No. 2 fuel oil, etc., then usually
about 0.001 to 0.5 %w, based on the weight of the total com-
position of the reaction product will be used. Concentrations
compriging a minor proportion, e.g., 15 to 45 /Ow of said reaction
product in a major amount of hydrocarbon diluent, e.g., 85 to 55
/Ow mineral lubricating oil, with or without other additives
present, can also be prepared for ease of handling.
~20ss~o
In the above compositions or concentrates, other conventional
additives may also be present, including dyes, pour point depres-
sants, antiwear, e.g., tricresyl phosphate, zinc dialkyl dithio-
phosphates of 3 to 8 carbon atoms, antioxidants such as phenyl-
alpha-naphthyl-amine, tert-octylphenol sulphide, bis-phenols such
as 4,4'-methylene bis(3,6-di-tert-butylphenol), viscosity index
improvers such as the ethylene-higher olefin copolymer,
polymethylacrylates, polyisobutylene, alkyl fumaratevinyl acetate
copolymers, and the like as well as other ashless dispersants or
detergents such as overbased sulphonates.
The invention is further illustrated by the following Exam-
ples.
Example 1
A 2-litre glass-bowl reactor equipped with a stirrer and
appropriate temperature control was utilized for the synthesis of
the star-shaped poly(isoprene) and the dispersant VI-improver.
Anionic polymerization techniques were employed and all reagents
such as:
monomers, solvents, initiators, etc. were dry and of high purity.
The polymerization was achieved under an inert gas such as argon
or nitrogen in order to avoid contamination with the atmosphere.
The reactor was charged with 1170 grams of cyclohexane and
heated to 35C. A small amount of 1,1-diphenylethylene was then
added to serve as an indicator for the subsequent titration.
Incremental additions of sec-butyllithium were introduced
into the reactor until a permanent yellow colour was reached. This
~erved a~ an indicator that all impurities had been scavenged from
the system. The solution was then back titrated with solvent until
the yellow colour had ~ust disappeared. The required amount of
initiator was then charged, which was calculated to be 5.7x10 3
moles of sec-butyllithium. To this ~olution was then added 294 mls
of isoprene monomer. The temperature was allowed to increase to
60C, where the polymerization continued for 2 hours. To the
~Z~590
_ 13 _
living poly(isoprene) was next added 00028 moles of commercial
divinylbenzene, such that the molar ratio of divinylbenzene to
sec-RLi was 5:1. The reaction was allowed to proceed for 1-2 hours
at 60GC. The solution turned deep red after addition of the di~Jinyl-
benzene. This divinylbenzene coupling formed the star-shaped
poly(isoprene). After the coupling step, 0.87 grams of 2-vinyl-
pyridine was added to the solution giving the polymer a chemically
bonded polar group. The polymer was then precipitated into a large
excess of isopropanol, filtered, and dried in a vacuum oven until
a constant weight was obtained.
Analysis of the polymer by Kjeldahl nitrogen analysls in-
dicated that the polymer contained from 350 to 450 ppm nitrogen.
This corresponds to around 0.5 ZOw 2-vinylpyridine in the polymer.
G.P.C. analysis of the polymer revealed the number-average
arm molecular weight to be 38,000 and the functionality was
observed to be around 9-10 arms. The polymer was stabilized with
Ionol and stored until needed for subsequent hydrogenation.
Stoichiometric Hydrogenation
Hydrogenation of the 2-vinylpyridine functionalized
starshaped poly(isoprene) was achieved with para-toluenesulphonyl-
hydrazide in refluxing xylene. A one-litre, four necked reaction
flask, fitted with a condenser, nitrogen inlet, thermometer, and
sample port was assembled and heated with a silicone oil bath.
The reaction flask was charged with 300 mls of xylene, to
which was added 5 grams of polymer. The reactor was heated to 60C
to aid polymer dissolution. Once the temperature had stabilized,
0.304 mole6 of para-toluenesulphonylhydrazide was added through a
powder funnel to the reaction. This amounts to a 4 to 1 molar
ratio of para-toluenesulphonyl-hydrazide to polymer double bonds.
The reaction medium was then heated to the reflux temperature of
xylene (130-135C) and allowed to react for 5 hours. The hydrogen-
ated product was recovered~by filtering the hot xylene solution,
followed by coagulation of the polymer solution in isopropanol.
~ ~ .
lZOSS90
_ 14 _
The polymer was washed several times with hot water and isopropa-
nol to remove any unreacted by-products. The polymer was then
dried overnight in a vacuum oven at 50C.
Analysis of the polymer by an O3 titration technique, re-
sulted in a 98% yield for the degree of hydrogenation. G.P.C.analysis of the polymer after hydrogenation likewise indicated
that no polymer degradation took place during the reaction.
Example 2
A 20-gallon (76-litre) stainless steel batch reactor was
employed for the synthesis of the dispersant VI-improver. To the
reactor was charged 8.8 gallons (33 litre) of cyclohexane, followed
by 7.8 pounds (3.5 kg) of isoprene monomer. This solution was
titrated with sec-butyllithium, and then the required amount of
sec-butyllithium was added (0.118 moles) to initiate the poly-
merization. The reaction was allowed to proceed at 60~C for 2hours, at which poi nt 64.4 grams of commercial divinylbenzene was
added. The star-coupling reaction was allowed to continue for 1-2
hours at 60~C. Next, was added 18.5 grams of 2-vinylpyridine to
the solution to form the chemically bonded polar group. The
polymer cement was terminated with methanol, and then stabilized
with an anti-oxidant and stored until needed for subsequent
hydrogenation.
K~eldahl nitrogen analysis indicated 460 ppm nitrogen, which
amount~ to 0.3-0.4 a/oWt 2-vlnylpyridine.
G.P.C. analysis of the polymer revealed the number average
arm molecule weight to be 32,000, and the functionality was
observed to be around 9-10 arms.
Catalytic Hydrogenation
To hydrogenate the star-polymer as described above, a ca-
talytic hydrogenation technique was employed. This method involves
sub~ecting the polymer cement to catalyst comprising the reaction
product of an aluminium alkyl and a nickel carboxylate, more
specifically triethyl-aluminium and nickel octoate.
:.
lZ055~0
~s
To a 10 gallon (38 litre) stainless steel autoclave reacto~,
equipped with a stir~e}, hydrogen inlet, and appropriate tem-
perature control, was charged ~2 pounds (18.9 kg) (6.5 gallons)
(24.7 litre) of a 12~ow polymer solution in cyclohexane. The
5 reactor was then heated to 40C. This charge amounts to 5.04
pounds (2.27 kg) of neat polymer.
The autoclave was then pressurized with hydrogen to 750 psi
(52.5 bar) followed by the addition of 5,959 ml of the catalyst
solution of a 6,000 ppm nickel concentration. The catalyst solution
] was added in three increments (i.e., 1,986 ml per increment) being
careful not to allow the temperature to increase beyond 70C. (The
overall amount of catalyst added was 1,500 ppm). The reaction
temperature was maintained within 60-70C for 4 hours at which
point the conversion, as determined by 03 titration, was found to
lS be 98%.
The reaction was allowed to continue overnight resulting in a
final degree of hydrogenation of 98.4%. After completion of the
hydrogenation step, the polymer cement was sub~ected to several
citric-acid wash cycles to remove the residual nickel from the
20 polymer. Analysis of the polymer by an atomic absorption technique
indicated the remaining nickel concentration to be on the order of
155-160 ppm nickel based on the weight of neat polymer. Ionol
ant~-oxidant was added to the cement and the polymer cement was
stored until needed. The polymer could be easily isolated, by
coagulation into isopropanol, followed by vacuum drying.
Product Evaluation
The disper6ancy of the star-shaped polymer was assessed by a
spot dispersancy test (SDT). The new dispersant VI-improvers were
evaluated and compared to known commercial dispersant VI-improvers
such a6: Amoco 9250, Lubrizol 6401 and Acryloid 1155. Acryloid
1155 i6 a nitrogen functionalized ethylene-propylene random
copolymer. Lubrizol 6401, an ashless dispersant, is a polyisobu-
tylene-maleic anhydride graft copolymer functionalized with
~205590
_16
pentaerythritol. Amoco 9250 is a poly-~sobutylene-amlne ashless
dispersant also containing boron. The spot dispersancy test is a
qualitative measure of the ability of an oil to disperse sludge.
In these tests a 2%w solution of the additive was added to a
5 common lubricating oil base stock, is mixed with a sludge-con-
taining oil and heated to 149C for 15 minutes and shaken for one
hour. The samples were then left in an oven overnight at 149~C.
The samples were next allowed to cool to room temperature and two
drops of the solution were placed, with an eye dropper, on se-
10 parate 12 cm diameter No. 1 whatman filter papers. Ihe diametersof the spots were measured after 24 hours. The longitudinal and
latatudinal diameters of the inner sludge spot were measured in
millimetres (mm) and an average diameter was taken. Xn a similar
fashion, the average outer diameters of the oil spot was measured.
lS The ratio of the inner spot diameter to the outer spot diameter is
known as the SDT ratio, a larger rztio indicating better dis-
persancy. Table I summarizes the data, comparing the commercially
known dispersant VI~improvers to a blank control, and the 2-vinyl-
pyridlne func~ionalized star-shaped hydrogenated poly~isoprene).
~zoss9~
_ 17-
TABLE I
SPOT DISPERSANCY TEST
SAMPLE (SDT RATIO ~)
(1) Blank 76
(2) Blank + Amoco 9250 (2 ~Ow) 79
(3) Blank + Lubrizol 6401 ~2 ~Ow) 83
(4) Blank + Acryloid 1155 (1.2 ~Ow) 81
(5) Blank + Acryloid 1155 (2.4 ~/~w) 81
(6) Blank + Star-PI-(2vp) (1.2 r/oW) 87
10 (7) Blank + Star-PI-(2vp) (2.4 ~/Ow) 94
As observed from Table I, the dispersancy of the hydrogenated
2-vinylpyridine-star-poly(isoprene) is excellent, being much
higher than the commercial dispersant VI-improvers used for
comparison.
l5 A viscometric comparison of the dispersant VI-improver and a
similar star-shaped poly(isoprene) without 2-vinylpyridine function-
ality was made and the data are summarized in Table II.
TABLE II
VISCOMETRIC COMPARISON
TESTDISPERSANT VI NON-DISPERSANT VI
Vk, cSt, 40C 117 84.2
Vk, cSt, 100C18.58 13.9
Viscosity Index 178 172
Vd, -18C, cP 2,100 2,060
25 Vd~ -25C, cP 19,691 15,132
The kinematic viscosity data a~ mea~ured at both high and low
temperatures indicate the polymer has good thickening capability,
qualifying this polymer as a suitable VI-imrover as well as a
dispersant. These superior properties make the hydrogenated
star-poly(isoprene) with 2-vinylpyridine groups an excellent
dispersant VI-improver.
