CA1168223A - Hydrocarbon solutions of polymers having an improved resistance to mechanical degradation - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The resistance to mechanical degradation of poly-mer modified lubricating oils can be improved by reducing the elastic character of the fluids at a given viscosity and polymer concentration. Stored energy per bond, which is the energy for degradation, and which is provided by the flow process, is related to this elasticity. This stored energy can be reduced by altering the molecular weight distribution and molecular topology, i.e., macroscopic structure (linear, branched and ring structures) of the polymer. When a polymer solution is deformed, part of the energy is expended as viscous dissipation (i.e. heat) and part causes deformation of the polymer molecules which stores energy rather than dissipating it. The amount of energy the molecules can store is measured by their compliance, which indicates for example how much the chains will retract when the stress is removed. A large compliance means that the molecules deform easily when stress is applied. Stored energy per volume of solution is quantitatively related to the elasticity of the solutions through the compliance of the solution. This solution compliance depends on the com-pliance of the polymer molecules and their concentration.
Rules are formulated using the compliance which permit selection of MWD and molecular topology to maximize mechan-ical stability. Nonlinear structures and particular MWD
classes are claimed.

Description

1 ~ 68~

1 This invention relates to hydrocarbon solutions of

2 polymers having improved resistance to mechanical degradation

3 and the preparation thereof. More particularly, it relates to

4 viscosity index improving additives for mineral oils of lub-ricating viscosity by the addition thereto of macromolecules 6 whereby the mineral oil is provided with increased resistance 7 to mechanical degradation of the viscosity of said lubricating 8 oil composition.
9 As is well known ~o those skilled in the art, lu-bricating oils may be evaluated by many criteria each of which 11 relates to the proposed use of ~he oil. One of the more im-12 portant of these criteria is the viscosity inde~
13 It is known that the viscosity index of lubricating 14 oils can be usefully modified by the addition of oil-soluble polymeric viscosity index (V.I.) improvers such as polyesters 16 and polyolefins, e.g. butadiene-isoprene copolymers, poly-17 isobutylenes and ethylene copolymers including ethylene-higher 18 alpha-olefin copolymers and terpolymers; however, such an 19 addition can introduce chemical instability.
Recently, ethylene-propylene copolymers have become 21 widely used as viscosity improvers in lubricating oils because 22 of the low treat levels and improved viscometric properties.
23 The patent literature is replete with many publica-24 tions dealing with ethylene copolymers including tri- and te~rapolymers containing one or more types of dienes introduced 26 for a variety of reasons including a means to introduce branchi-27 ness into the ethylene polymer and to provide a means for croQs-28 link~ng said polymer through introduction of a crosslinking 2~ agent reactive with a portion of said diene. Those patents, how~ver, dealing with ethylene tri- and tetrapolymers added 31 to a mineral oil as a viscosity index modifying additive are 32 Of li~ited number and are best illustrated by the specificat~on 33 of U.S. Patent 3,790,480. This specification teaches ethylene 34 ter- and tetrapolymers involving ethylene, a C3 to C18 higher alpha-olefin, for example, propylene, and two classes of dienes 36 based upon the relative polymerizabilities of each of the 1 double bonds. In one class of dienes (as represented by 2 1,4-hexadiene) only one of the double bonds is readily 3 polymerizable whereas in the other class (as represented 4 by 2,5-norbornadiene) both double bonds are readily poly-S merizable. It is taught therein that an ethylene polymeric 6 viscosity index additive for mineral oils is superior when 7 and if it is an ethylene tetrapolymer containing both 8 classes of dienes rather than the prior art ethylene ter-9 polymer containing the class of dienes having only one readily polymerizable double bond. Allegedly, this super-11 iority obtains because the introduction of the second 12 diene comonomer with two readily polymerizable double bonds 13 into the terpolymer composition provides a significant in-14 crease in bulk polymer viscosity with only a minor increase of the inherent viscosity (see col. 8, lines 23-30) and 16 without degradation of the property of the terpolymer to 17 provide viscosity index improvement to mineral oils. Un-18 fortunately, these polymers as well as ethylene-propylene 19 copolymers generally in lubricating oil solutions are mech-anically degraded during lubrication of the operating device 21 and/or machine by exposure to the shear and operational 22 stresses resulting in instability and/or reduction of the 23 viscosity modifying activity of the ethylene copolymers.
24 Although believed misleading, U.S. 3,790,480 teaches (col. 6, lines 22-28) that optimum shear stability is achieved with 26 ethylene copolymers when the molecular weight distribution 27 is relatively narrow (preferably when the MW/Mn is less than 28 about 8). The (Mn) and (Mw) are measured by the well-known 29 techniques of vapor pressure (VPO) or membrane osmometry and light scattering, respectively.
31 This mechanical degradation of polymers in solution 32 is not limited to ethylene copolymers but applies to polymers 33 in general, including other types of known V.I.-improving 34 polymers, e.g. polybutadienes, polystyrene and polyesters, as is apparent from a U.S. Department of Commerce National 36 Technical Information Service Publication AD-A038139 of 1 June 1976 entitled "Mechanical Shear Degradation of Polymers 2 in Solution: A Review by J. Knight" or "Polymer Stress 3 Reactions" A. Casale, R. Porter Academic Press 1978. In 4 these reviews, an attempt is made to correlate shear stab-ility with molecular parameters, such as the effects of 6 molecular weight (~) and molecular weight distribution (M~D), 7 solvent, concentration and structure of repeat unit. With 8 regard to molecular weight distribution, it is stated that g polymers above a critical molecular weight will rupture under a given stress leading to a narrowing of the molecular weight 11 distribution. With regard to polymer type, it is believed 12 that degradation is correlated with the strength of bonds 13 and degree of chain flexibility. Nothing is concluded about 14 molecular topology. By topology we mean the connectivity of polymer backbone's contour e.g. linear, large and/or flexible 16 ring of long-chain branch-containing polymers, said rings or 17 branches will generally contain 100 or more backbone carbon lR atoms.
With regard to molecular topology, in U.S. Patent 4,077,893 it i8 stated that the viscosity index of lubricat-21 ing oil~ can be improved by a two-block copolymer of styrene 22 and hydrogenated isoprene or a hydrogenated "star-branched"
23 type polymer (which i8 a unique topological type) claimed to 24 have greatly improved mechanical shear stability which poly-mer m~y or may not be reacted with an alkane polyol having 26 at least two hydroxy groups (see col. 1, lines 10-18 and 27 50-55). No explanation of this polymer's claimed superiority 28 is given.
29 It is an object of this invention to provide polymer solutions having viscosity index improving actlvity for 31 mineral oils of lubricating viscosity which have increased 32 resistance to mechanical degradation. More particularly, 33 it is an object of this invention to provide polymer solu-3~ tions of improved resistance to mechanical stress over that exhibited by polymer solutions formulated from polymers of 36 equivalent thickening efficiency and the same chemical repeat 37 units.

4 ~ lLt;82Z3 1 It has been discovered that solutions ~f polymers at 2 a concent~ation such that ~n ]c ranges from one-tenth to 3 five (where ~n ] is the intrinsic viscosity of the poly~er 4 in the oil and c is the concentration in the same units e.g.
if [n] is in ml/gm then c must be gm/ml) exhibit increased 6 or enhanced stability to vis osity loss to polymer degrada-7 tion when this solution is subjected to mechanical stress9 8 if the compliance of said solution is no larger than twenty, 9 preferably 10, times the value exhibited by a linear mono-lo disperse polymer of the same chemical structure and of the 11 same weight average molecular weight (Mw).
12 Thus, the above ob3ective can be met by a lubricating 13 composition which comprises, according to this invention, a 14 mineral oil of lubricating viscosity and at least a viscosity index improving amount of an oil-soluble ~olymer of weight 16 average molecular weight of from about 10 to 107, said 17 polymer being characterized by providing an oil solution 18 which at a concentration such that [~ ~ c ranges from 0.1 to 19 5 provides a compliance of said polymeric solution no larger t~lan 20, pre~erably 10, ~ore preferably 5, optimally 3 times 21 the value exhibited by a linear monodisperse polymer of the 22 same chemical structure as said polymer and of the same 23 weight average molecular weigh~ (all ~ herein are deter-24 mined by light scattering techniques). The actual value sel-ected for the limit for the compliance will be determined by 26 the thickening efficiency, severity of use condition and 27 acceptable limits on degradation for the use. This invention 28 teaches how to meet the criteria once a permissib9e degrada-29 tion level is secured which value for purposes of V.I. im-proving activi~y has been selected as a maximum value of 20 31 (it must be realized that the lower value of the range can 32 be less than 1 and for this reason only the upper limit has 33 been defined).
34 Im~licit in this discovery that the control of the compliance level of polymer solutions at a given viscosity 36 modification level can provide for improved mechanical shear resistance of said solutions, is a finding that said resistance is a function of both the molecular weight distribution (MWD) of and the molecular topology of said polymer. For purposes of this disclosure, the compliance Je is set forth in the following equation:
o JeRMw MzMz+l (11 -Jo cRT ~w2 nO2 wherein JeR is the reduced compliance which depends on mole-cular topology. JeR can be determined experimentally and estimated theoretically in the prescribed concentration range.
(See for example J.S. Ham, J. Chem. Phys., 26 625 (1957)~.
In the equation n is the viscosity of the polymer solution at concentration c; ~ s is the viscosity of the unmodified oil; T is temperature; and, R is the gas constant.
Je can be measured experimentally as to a so-called elastic parameter of the fluid and is related to the normal stresses exerted in shearing flow as J = lim 12 (~o) C ~

where ~ is the strain rate and Pll-P22 is the first normal stress difference (see for example W.W. Graessley Adv. Polymer Sci., 16, 60 (1974)).
Molecular weight is designated herein as M. Mz, Mz+l, Mw and Mn are molecular weight averages, see for example, "Science and Technology of Rubber", F. Eirich, editor, Wiley 1978, p. 83ff. These molecular weight averages (MaV) may be determined by a combination of gel permeation chromatography and on-line light scattering forming the sums over the chromatogram as Mav ~ ci where a = 0,1,2 or 3 respectively for the number weight, z and z+l average molecular weights, and where Ci is the concentration 6- ~

1 of polymer subfraction i which has scattering intensity R9i 2 above that of the solvent and K is the appropriate scattering 3 constant and a is the scattering angle,which is small; e.g.
4 less than 5 degrees.
Alternatively, these molecular weight averages may 6 be obtained by ultracentrifugation techniques.
7 It will be shown that for a given n and c, a reduc-8 tion in Je correlates with improved shear stability. This 9 variation in Je can be brought about by lowering JeR
through branching or ring formation and/or by changing MWD
11 as defined by ~ Mz+l. The literature suggests that the 13 ~ 2 14 shear-stable polymer MWD range can be chosed by selection of an appropriate Mw/Mn value wherein tMn) is the number 16 average molecular weight. This approach is insufficient, 17 not adequately discriminatory and/or sufficiently accurate 18 for practice of th~s invention since the ratio does not 19 articulate tho5e polymeric structures which provide the im-proved resistance to mechanical stress of polymer solutions 21 so that the advantages of the invention may be realized.
22 Mechanical degradation is caused by stress assis~ed 23 chemical bond rupture of the polymer backbone chains. A
24 direct measure of the stress per bond caused by flow in 2~ linear polymers is the stored energy or normal stress. Thus, 26 for a given set of chemical constraints, concentration, and 27 a given vi~cous dissipation, it is anticipated that in 28 situations where a higher stored energy per molecule exists 29 more degradation will occur. Since in dilute or semi-dilute polymer solutions, branched and loop containing poly-31 meric structures of the same molecular weight have lower re-32 duced compliances than do linear ones (at least in the linear 33 viscoelastic region), it is proposed that they should degrade 34 less. In addition to lower stored energy per molecule, the connectivity of non-linear structures leads to lower stress 36 per bond, e.g. four-arm star structures are anticipated to have z~;~

1 only about half the stress per bond near the molecule~s cen-2 ter that would be experienced by a linear molecule storing the 3 same energy. It is the sum of these two effects which is of importance. Since, as inferred below, non-linear molecules

5 have lower [ n ] and thus thickening efficiency for a given

6 Mw and MWD, it is not immediately clear whether the higher Mw

7 needed for non-linear structures to reach the same thickening

8 efficiency as linear ones, will cause the compliance and stored

9 energy/bond to be greater for the non-linear molecules at the

10 same thickening efficiency. For the particular case of star-

11 branched molecules coupling of these effects in a calculation

12 of the maximum stored energy per bond using the Rouse model

13 (see J. S. Ham or W. ~J. Graessleyreferences above for Rouse

14 model) results in the following ratio of maximum stored en-lS ergy per bond for branched and linear structures at the same 16 [ n ] and c: 2 17 Maximum stored energy per bond of Branched Structure=(l6 f-l)f 18 Linear Structure (3 f-2)3 19 where f is the number of equal length arms in the star (f = 2 20 for a linear molecule). This is a decreasing function of f 21 indicating even at the same thickening efficiency (and MWD) 22 star-branched structures should degrade less. Although the 23 solution viscosity (in the prescribed [ n ]c range) of a branch-24 ed polymer of a given molecular weight continues to decrease as`
25 the number of branches (f) increases, there is a limit to how 26 much the stored energy per bond can be reduced. For the case 27 at hand, with [ n ] and c constant, the maximum stored energy/
28 bond can be reduced to 16/27 of the value for a linear polymer 29 when the number of branches becomes large. Thus one might ex-30 pect reduced effectiveness of additional branching at high 31 branching degrees. The preferred range for the degree of 32 branching (f) is between 5 and 16. This calculation was per-33 formed for a particular branch type and molecular model for 34 behavior in the linear viscoelastic region. Other branched 35 and loop-containing structures should behave similarly. Simi-36 lar calculations should give the proper ordering of behavior in - 8 - ~ 23 1 the non-linear region. In Example 1, we show experimentally 2 that lightly branched structures do degrade less than their .3 linear counterparts at the same [ n ] and c. Finally, ~ once bond rupture occurs, the rate of viscosity (and normal stress) loss per break will be less for the non-linear struc-6 tures. This is so in dilute to semidilute solution, where 7 the viscositv increment caused by the polymer will be propor-8 tional to [~ ]c. ExperimentallY, [n ]NONLINEAR=f(~) [n]LINEAR' 9 where polymers of the same molecular weight are 10 considered and f (g) < 1 is a function of the molecular topo-g G NONLINEAR/< ~G ~ ~INEAR-<RG2>is the mean 12 square radius of gyration of the polymer. Since f (g) increases 13 with g and any scission process will tend to make the average 14 g for the polymer molecul~ in solution larger, one can see

15 that the incremental change in intrinsic viscosity with the

16 molecular weight (d [ n ]/dM) will be less for non-linear struc-

17 tures than for linear polymeric structures. Two additional

18 points worth noting are that the incremental change in mole-

19 cular weight with number of bond ruptures (dM/d (bond rupture)]

20 will vary with topology and will always be less for non-linear

21 structures. For the first bond rupture on a ring it is zero,

22 and [ n ] will actually increase.

23 It is well known in polymerization reactions that

24 both the polymeric MWD and the intrinsic viscosity of poly-

25 mers can be readily manipulated by varying the reaction com-

26 ponents and conditions. Since this knowledge is well known,

27 it will not be necessary to go into a description of obtaining

28 the desired MWD and/or intrinsic viscosity.

29 The invention herein relates to enhancement of all types of polymer solutions generally; however, for purposes 31 of illustration the specific teaching of the invention is 32 directed to selected types of polymeric viscosity index 33 (V.I.) improver additives for lubricating oil compositions 34 which additives are characterized by the property of reducing the extent of the formulated oil's viscosity change as a li~;8223 i resul t o tem~era~ure ~hange. These polymeric mate~ials are 2 oil-soluDle an~ possess a linear an~ extended metnylene 3 chaln (de_ived _rom the polymer-zation of an ethylenically 4 unsaturated nome,) which provides for said oil-solubility.
These V.I. im~roving polymers are hydrocarbon polymers having 6 a ~ ranging from 15,000 to 10,000,000, preferably 20,000 7 to 2,000,000. The specific preferable range depends on the 8 composition and topology of the polymer selected. The 9 main hydrocarbon chain may have hydrocarbon substituents which can be connected either directly via carbon atoms or 11 indirectly via one or more other atoms, such as oxygen, 12 sulfur, nitrogen and phosphorous, although it is preferred 13 that the connecting atom be either carbon or o~ygen.
14 Thus, the useful hydrocarbon solutions of the invention normally contain from 0.5 to 10 weight percent polymeric 16 viscosity index improvers which include olefin polymers such 17 as polybutene, atactic polypropylene, ethylen~-propylene 18 copolymers including ter- and tetrapolymers, hydrogenated l9 polymers and copolymers and terpolymers of styrene with isoprene and/or butadiene, polymers of alkyl acrylates or 21 alkyl methacrylates, copolymers of alkyl methacrylates with 22 N-vinyl pyrollidone or dimethylaminoalkyl methacrylate, 23 poly (alkyl styrenes), alk~-lene polyethers, alkyl fumarate-24 vinyl acetate copolymers, post-grafted interpolymers of ethylene-propylene with an active monomer such as maleic 26 anhydride which may be further reacted with an alcohol or 27 an alkylene polyamine, styrene/maleic anhydride polymers 28 post-reacted with alcohols and amines, ethoxylated deriva-29 tives of acrylate polymers, etc.
Commonly used are oil-soluble polymers of isobutylene.
31 Such polyisobutylenes are readily obtained in a known manner 32 as by following the procedure of U.S. P~t. No. 2,084,501 33 wherein the isoolefin, e.g. isobutylene, is polymerized in 34 the presence of a suitable Friedel-Crafts catalyst, e.g.
boron fluoride, aluminum chloride, etc., at temperatures 36 substantially below 0C. such as at -40C. Such polyiso-1 butylenes can also be polymerized with a higher straightchained alpha-olefin of 6 to 20 carbon atoms as taught in 3 U.S. Pat. No. 2,534,095 where said copolymer contains from 4 about 75 to about 99% by volume of isobutylene and about 1 S to about 25% by volume of a higher normal alpha-olefin of 6 6 to 20 carbon atoms.
7 Other polymeric viscosity index modifier systems used 8 in accordance with this invention are: copolymers of 9 ethylene and C3-C18 monoolefins as described in Canadian Pat. No. 934,743; copolymers of ethylene, C3-C12 mono-11 olefins and C5-C8 diolefins as described in U.S. Pat. No.
12 3,598,738; mechanically degraded copolymers of ethylene, 13 propylene and if desired a sm~ll amount, e.g. 0.5 to 12 14 wt.%, of other C4 to C12 hydrocarbon mono- or diolefins as taught in U.S. Pat. No. 3,769,216 and U.K. Pat. No. 1,397,994;
16 a polymer of conjugated diolefin of from 4 to 5 carbon atoms 17 includ~ng butadiene, isoprene, 1,3-pentadiene and mixtures 18 thereof as described in U.S. Pat. No. 3,312,621; random 19 copolymers of butadiene and styrene which may be hydrogenated as described in U.S. Pat. Nos. 2,798,853 and 3,554,911; and 21 hydrogenated block copolymers of butadiene and sty~rene as 22 described in U.S. Pat. No. 3,772,169; random or block in-23 cluding hydrogenated (partially or fully) copolymers of 24 butadiene and isoprene with up to 25 mol percent of a C8-C20 monovinyl aromatic comp~und, e.g. styrene, as described 26 in U.S. pat. No. 3,795,615; graft copolymers of polystyrene 27 and polyisobutylene (see U.S. 3,992,310); 4-methyl-1-pentene 28 interpolymers (see U.S. 3,320,968) esterified olefin (in-29 cludes both C2_4 alpha-olefins and styrene) alpha, beta unsaturated aliphatic acid or anhydride interpolymers (see 31 U.S. 4,080,303); and graft copolymers of butadiene-sty~rene 32 (see U.S. 4,085,055).
33 Ethylene_Copolymers 34 One subgroup of V.I. improvers useful for preparing solutions according to this invention are ethylene co-36 polymers of from about 2 to about 98, preferably 30 to 80, ~t~ X.'~;~

l optimally 38 to 70 wt~o/o of ethylene and one or more C3 to 2 C30 higher alpha-olefins, preferably propylene, which have 3 a degree of crystallinity of less than 25 wt.%, as deter-4 mined by X-ray or differential scanning calorimetry, and have a Mw in the range of about 104 to about 107. These 6 ethylene copolymers are prepared from ethylenically un-7 saturated hydrocarbons including cyclic, alicyclic and 8 acyclic monomers containing 2-30 carbons. The higher alpha-g olefins which may be used in the preparation of the ethylene copolymers used in the practice of this invention include ll those monomers which are linear, or short-chain branched 12 where the branching occurs three or more carbon atoms from 13 the double bond. Mixtures of C2 to C30 olefins may be 14 employed. Suitable examples of the preferred range of C3 to C18 alpha-olefins include propylene, l-butene, l-pentene, 16 l-hexene, l-heptene, l-octene, l-nonene, l-decene, 4-methyl-17 l-pentene, 4-methyl-1-hexene, 5-methyl-1-hexene, 4, 4-di-18 methyl-l-pentene, 4-methyl-1-heptene, 5-methyl-1-heptene, 19 6-methyl-1-heptene, 4,4-dimethyl-1-hexene, 5,6,5-trimethyl-l-heptene and mixtures thereof. It is preferred however, 21 that the ethylene monomer be copolymerized with propylene.
22 Ethylene Ter- and Tetrapolymers 23 The terpolymers employed in the instant invention are 24 well-known. For example, ethylene-propylene-non^con~ugated diene terpolymers are well-known; they can be prepared using 26 Ziegler-Natta catalysts. These terpolymers, which are 27 primarily produced for use in elastomeric compositions, are 28 characterized by the absence of chain or backbone unsatura-29 tion and contains sites of unsaturation in groups which are pendant to or are in cyclic structures outside of the main 31 polymer chain.
32 Useful copolymers for the production of the solutions 33 of this inventioncomprise ethylene, a C3 to C8 straight or 34 branched chain alpha-olefin and a non-conjugated diene.
Representative non-limiting examples of non-con3ugated 36 dienes that may be used as the third monomer in the terpolymer l include:
2 a. Straight chain acyclic dienes such as:
3 1,4-hexadiene; 1,5-heptadiene, 1,6-octa-4 diene.
b. Branched chain acyclic dienes such as: 5-6 methyl-1,4-hexadiene; 3,7-dimethyl 1,6-7 octadiene; 3,7-dimethyl 1,7-octadiene; and 8 the mixed isomers of dihydro-myrcene and 9 dihydro-cymene.
c. Single ring alicyclic dienes such as: 1,4-ll cyclohexadiene; 1,5-c~cloctadiene,1,5-cyclo-12 dodecadiene, 4-vinylcyclohexene; 1-allyl,4-13 isopropylidene cyclohexane; 3-allyl-cyclo-14 pentene; 4-allyl cyclohexene and l-iso-propenyl-4-(4-butenyl) cyclohexane.
16 d. Multi-single ring alicyclic dienes such as:
17 4,4'-dicyclopentenyl and 4,4'-dicyclo-18 hexenyl diene~.
19 e. Multi-ring alicyclic fused and bridged ring dienes such as: tetrahydroindene; methyl 21 tetrahydroindene; dicyclopentadiene; bicyclo 22 (2.2.1) hepta 2,5-diene; alkenyl, alkylidene, 23 cycloalkenyl and cycloalkylidene norbornenes 24 such as: 5-methylene-6-methyl-2-norbornene;
5-methylene-6,6-dimethyl-2-norbornene; 5-26 propenyl-2-norbornene; 5-(3-cyclopentenyl)-2-27 norbornene and 5-cyclohexylidene-2-norbornene.
28 In general, useful terpolymers contain non-conju-29 gated dienes having 5 to 14 carbon atoms and exhibit Mw molecular weights of from lO to lO . Preferred dienes 31 include ethylidene norbornene, dicyclopentadiene, 1,4-32 hexadiene and 2,5-norbornadiene.
33 Structurally, the terpolymers suitable for the 34 polymeric solutions of the present invention may be illus-trated for various non-conjugated diene monomers as random 36 terpolymers in which the following moieties are linked in 22;3 1 the polymer chain in a more or less random sequence and in 2 a varying number as illustrated in ,the following:

Xigher ~thylene alpha-olefin 1,4-hexadiene units units H H
2 CH2 ~ C ~ H2 CH ~ (2) HC CH
\f H 2 HC CH
3Ethylene Dicyclopentadiene Hi~her-al~ha units units olefin units ~ C- C ~ ~2 lCH ~ ~H2 2 HC~ CH2 ~ H
H2C - C ~ CH - CH3 5-ethylidene- higher alpha- Ethylene 2-norbornene olefin units units units 4 wherein x, y and z are cardinal numbers and R are alkyl groups.
5 While these terpolymers are essentially amorphous in character, 6 they may contain up to about 25 percent by weight of crystal-7 line segments as determined by X-ray or differential scanning 8 calorimetry. Details on these methods for measurements of 9 crystallinity are found in J. Polymer Science, A-2, 9, 127 (1971) by G. Ver Strate and Z. W. Wilchinsky.
11 Terpolymers, u8eful in the present in~ention contain 12 at least 30 mol percent, preferably not re than about 85 13 mol percent of ethylene; between about 15 and about 70 mol :L percent o' a higher alpha-olefin or mixture thereof, pre-;2 ferably propylene; and between 1 and 20 mol percent, 3 preferably 1 to 15 mol percent, of a non-conjugated diene 4 or mixture thereof. Especially preferred are polymers of about 40 to 70 mol percent ethylene, 20 to 58 mol percent 6 higher monoolefin and 2 to 10 mol percent diene, On a 7 weight basis, usually the diene will be at least 2 or 3 8 weight percent of the total terpolymer.
9 Suitable copolymers may be prepared in either 10 batch or continuous reactor systems. In common with all 11 Ziegler-Natta polymerizations, monomers, solvents and 12 catalyst components are dried and freed from moisture, 13 oxygen or other constituents which are known to be harm-14 ful to the activity of the catalyst system. The feed tanks, lines and reactors may be protected by blanketing with an 16 inert dry gas such as purified nitrogen. Chain progaga-17 tion retarders or stopper~, such as hydrogen and anhydrous 18 hydrogen chloride, may be fed continuously or intermit-19 tently to the reactor for the purpose of controlling the molecula~ weight and/~r M~D within the desired 21 limits.
22 Alkyl Styrene Polymers 23 Those useful polymeric materials are produced by the 24 polymerization of compounds of the formula (4) CH2 = C - P (4) ~
~ Ç

26 wherein Rs and R6 are the same or different and selected 27 from hydrogen and alkyl radicals having from 1 to about 20, 2~ preferably from 3 to 10, carbon atoms. Compounds within 29 the scope of formula (4) useful herein include alkyl sty-renes, alpha alkyl styrenes and alpha alkyl alkylstyrenes.
31 Of these three types of compounds alkyl s~yrenes are the 32 most preferred for use herein.

1 ~ f~ 23 1 Alkyl styrenes are compounds within the scope of 2 formula (4) wherein R5 is hydrogen and R6 is selected from 3 alkyl radicals having from 1 to about 20 and preferably 4 from about 3 to about 10 carbon atoms.
Examples of alkyl styrenes useful herein include but 6 are not limited to n-propyl styrene, i-propyl 7 styrene, n-butyl styrene, t-butyl styrene (most preferred), 8 n-hexyl styrene, 2-ethylhexyl styrene, n-octyl styrene, etc.
9 Alpha alkyl styrenes are compounds within the scope of formula (4) wherein R5 is selected from alkyl 11 radicals having from 1 to about 20, and R6 is hydrogen.
12 Examples of alpha alkyl styrenes useful herein include 13 aLpha n-butyl styrene, alpha n-pentyl styrene, alpha n-hexyl 14 styrene (most preferred), alpha n-decyl styrene, e~c.
Alpha alkyl alkylstyrenes are compounds within the 16 scope of formula (4) wherein R5 is selected from alkyl 17 radicals having from 1 to about 20 and R6 is selected from 18 alkyl radicals having from 1 to about 20 carbon atoms.
19 Examples of alpha alkyl alkylstyrenes useful herein include alpha methyl n-butylstyrene, alpha methyl t-21 butylstyrene (most preferred), alpha methyl hexylstyrene, 22 alpha methyl ethylhexylstyrene, alpha ethyl t-butylstyrene, 23 alpha ethyl dodecylstyrene~ alpha butyl t-butylstyrene, 24 alpha butyl ethylhexylstyrene, alpha hexyl n-butylstyrene, alpha dodecyl methylstyrene, etc.
26 Styrene Copolymers 27 These are generally known as alkenylarene-con~ugated 28 diene interpolymers and include interpolymers of an alkenyl-29 arene monomer, such as styrene, and a conjugated diene 3~ monomer, such as butadiene, which have been preferably 31 fully hydrogenated to remove substantially all of the olefinic 32 unsaturation, although, in some situations, partial hydrogena-33 tion of the aro~atic-type unsaturation is effected. These 34 interpolymers are prepared by conventional polymerization techniques involving the formation of interpolymers having 36 a controlled type of steric arrangement of the polymerized :~ ~t;~

l monomers, i.e. random, block, tapered, etc. Hydrogenation 2 of the interpolymer is effected using conventional hydro-3 genation processes.
~I Hydrogenated alkenylarene-conjugated diene interpoly-mers of relatively high molecular weight are suitable herein.
6 SUch high molecular weight interpolymers include those which 7 can be characterized as having a molecular weight of 104 to 8 107. Preferred interpolymers have molecular weight in a 9 range of between about 30,000 snd about 150,000. Such interpolymers are known in the prior art.
11 Suitable alkenylarene monomers include vinyl mono-, 12 di- or polyaromatic compounds, such as a styrene or a vinyl 13 naphthalene monomer. The preferred alkenylarene monomers 14 are styrene, and substituted styrenes, such as alkylated sty;ene, or halogenated styrene. The alkyl group is the 16 alkylated styrene, which may be a substituent on the aromatic 17 ring or on an alpha carbon atom, may contain from 1 to about 18 20 carbon~, preferably 1-6 carbon atoms. Suitable conjugated 19 diene nomers include butadiene and alkyl-substituted buta-diene, having from 1 to about 6 carbons in the alkyl 21 substituent. Thus, in addition to butadiene, isoprene, 22 piperylene and 2,3-dimethylbutadiene are useful as the diene 23 monomer. Two or more different alkenylarene monomers as 24 well as two or more different conjugated diene monomers may be polymerized to form the alkenylarene-conjugated diene 26 interpolymers. The majority of these interpolymers known 27 in the prior art are copolymers prepared from one type of 28 each monomer.
29 A number of hydrogenated alkenylarene-con~ugated diene interpolymers are known in the prior art to be 31 effective viscosity index (V.I.) improvers for lubricating 32 oils.
33 U.S. Pat. Nos. 3,554,911; 3,630,905 and 3,772,169 34 are concerned with the use of hydrogenated random butadiene-styrene copolymers as V.I. improvers for lubricating oils.
36 These copolymers are prepared by the copolymerization, using x;~

1 conventional techniques, of butadiene and styrene in the 2 presence of a randomizing agent and subsequently the 1 copolymers are partially hydrogenated. The hydrogenated 4 copolymers have a ~ from about 10,000 to about 125,000;
preferred range of from 30,000 to 100,000. These copolymers 6 contain butadiene in the range of from 30% to 44% by weight 7 with the remainder being styrene. Prior to hydrogenation, 8 the copolymers have a vinyl content of less than 35% by 9 weight. During hydrogenation, the olef~nic group hydro-genation ~s 95% by weight or more, and the phenyl group 11 hydrogenation is 5% by weight or less.
12 U.S. 3,752,767 discloses a V.I. improver of hydrogenated 13 random copolymers of a conjugated diene and a vinyl aromatic 14 compound, in which the diene and/or the vinyl aromatic com-pound contains at least one alkyl substituent. These copoly-16 mers are further defined as derived from a C4 6 conjugated 17 diene and a styrene in which the diene and/or styrene con-18 tains at least one lower Cl_6 alkyl substituent. Dienes 19 include piperylene, 2,3-dimethylbutadiene, isoprene and butadiene. The vinyl aromatic compound is styrene or an 21 alkylated styrene. In the alkylated styrene, the alkyl 22 substituent may be attached to either the alpha-carbon of 23 the styrene, i.e., alpha-methylstyrene, or to the aromatic 24 ring, i.e., p-methylstyrene. The molar ratio between the conjugated diene and the vinyl aromatic compound varies depend-26 ing upon the nature of the vinyl aromatic component, since 27 the oil-solubility depends upon the presence or absence of an 28 alkyl substituent in the vinyl aromatic compound. Thus, 29 when the vinyl aromatic compound consists entirely of styrene, up to about 70 molar percent styrene may be utilized. When 31 the vinyl aromatic compound contains an alkyl group of 32 sufficient oil-solubilizing properties, e.g., p-t-butylsty-33 rene, up to about 90 molar percent may be used. These co-34 polymers are prepared by copolymerization, ~Ising conventional techniques, of the appropriate vinyl axomatic and conjugated 36 diene compounds in the presence of a randomizing agent and 1 subsequently, the copolymers are psrtially hydrogenated.
2 In the hydrogenated copolymer, it is preferred that m~re 3 than 95% of the olefinically unsaturated bonds and less than 4 5% of the aromatic unsaturation originally prese~t in the 5 random copolymer is saturated in the final hydrogenated 6 random copolymer. The Mw is in the range from 104 to 107.
7 U.S. 3,775,329 is concerned with the use of hydrogenated 8 tapered copolymers of isoprene and a monovinyl aromatic com-9 pound as V.I. ~mprovers for lubricating oil. These tapered 10 copolymers are defined as including both 'Isingle tapered 11 copolymers" and '~ultiple tapered copolymers". These 12 particular copolymers are derived from isoprene and a vinyl 13 mono-, di-, os polyaromatic compound, such as a sLy~-ene or 14 a vinyl naphthalene. ~he preferred vinyl aromatic monomers 15 are styrene, alkylated styrene, e.g. para-t-butyl styrene, 16 or halogen-substituted styrene. The copolymers are prepared 17 by the copolymerization, using conventio~al techniques, of 18 the appropr~ate monomers, and subsequently, the copolymers 19 are hydrogenated using conventional techniques to the de-20 sired degree of hydrogenation. It is preferred that 95%
21 of the olefinic unsaturated bonds originally present in the 22 tapered copolymer and less than 5%, of the aromatic unsatura-23 tion is saturated in the final hydrogenated tapered copolymer.
24 The ~ may vary between 104 to 107 and preferably in the 25 r~nge of from 20,000 to 200,000.
26 Other block copolymers include:
27 U . ~ . 3,668,125 is concerned with hydrogenated block 28 copolymers having at least three essentially uniform 29 polymer blocks, wherein one block type is a hydrogenated

30 monovinyl arene, e.g. styrene, polymer block and the other

31 is a hydrogenated conjugated diene, e.g., butadiene or

32 isoprene, polymer block; and, U.S. 3,763,044 is concerned

33 with a block copolymer corresponding to the general formula,

34 A-s, wherein A represents a polymer block of the group

35 consisting of polystyrene and hydrogenated polystyrene

36 products having a MW of from 5,000 to 50,000 and B represents 1 a block of hydrogenated polyisoprene having a ~ of 104 to 106.
3 The above discussed patents are mentioned to identify 4 and to illustrate both general and specific types of hydro-genated alkenylarene-conjugated diene interpolymers useful 6 as viscosity index improvers, which may be used to prepare 7 the additive solutions and lubricating compositions of the 8 present invention. Included herein also are graft copoly-9 mers of polystyrene and 15 to 50 wt.% of a polyisobutylene comprising a polystyrene backbone of molecular weight ll 50,000 to 1,000,000 having joined thereto polyisobutylene 12 groups of molecular weight 1,000 to 20,000 whereby each 13 polyisobutylene group is attached to the polystyrene back-14 bone.
Hydrogenated Coniugated Diolefin Polymers 16 These polymers are derived from conjugated dienes 17 having from 4 to 6 carbon atoms, most usefully, butadiene.
18 Examples are homopolymers of 1,3-butadiene, isoprene, 1,3-19 pentadiene, 1,3-dimethylbutadiene, copolymers formed with at least two of these conjugated dienes and copolymers of 21 the latter with styrene; these homopolymers and copolymers 22 having been hydrogenated up to the above-mentioned residual 23 unsaturation degree. More particularly, the hydrogenated 24 polymer may be obtained from:
Z5 a polymer of 1,3-butadiene, initially containing from 26 25 to 80% of 1,2 units;
27 a copolymer containing from 10 to 90% of butadiene 28 u~its and from 10 to 90% of isoprene urits; or, 29 a copolymer containing from 20 to 80% of units deri~ed from a conjugated diene having from 4 to 6 carbon 31 atoms and 20 to 80% of styrene units.
32 These polymers or copolymers may be prepared, for 33 example, in solution in an aliphatic or cycloaliphatic 34 solvent according to various techniques described in the prior art. They are preferably prepared by catalysis in 36 the presence of alkali metals derivatives in order to 1 1~822;~

1 3~~ei n ?-~cu_ts hav_-~ 2 ?~ar-ow -2nCe Q dist-~ h~u~lor. O
2 ~;~e ~GIe-ul~- weights.
3 The hyarogenatior. mav a;so ~e conauctea a~cording to 4 conventiz~al techr.iques, for example, in the p_esence of catalyst containing Raney nickel, platinu~" or palladium, deposited on carbon, or with systems obtained by 7 reaction of transition metal derivatives, such as nickel 8 or cobalt carboxylates or acetylacetonates, with organore-9 ducing compounds such as organoaluminum or organolithium compounds or their hydrides.
11 Highly useful is a hydrogenated copolymer of 12 butadiene and isoprene wherein the weight ratio of butadiene 13 to isoprene is between about 10:90 and 70:30; from about 14 30% to about 55~ of the precursor copolymer units are in the 1,4-configuration and wherein the olefinic bonds are 16 substantially saturated by hydrogenation, the average 17 molecular weight of the copolymer being from about 40,000 18 to about 225,000. The copolymer may include random, tapered 19 and block components.
The copolymers may be usefully grafted (by reaction 21 in the presence of a compound generating free radicals) 22 with from 1 to 40 wt. ~ more usually 1 to 10 wt. % of a 23 polymerizable vinyl compound such as vinyl acetate, N-vinyl-24 pyrrolidone, various acrylates and methacrylates.
The Ester Based Polymers 26 Usually these V.I.-improving, oil-soluble ester based 27 polymers will have molecular weights in the range of 104 28 to 107, preferably 50,000 to 500,000 and most preferably 29 50,000 to 200,000 Mw. These ester based polymers are derived essentially, e.g., 80 wt.% or more of the total 31 polymer, from C8 to C20, prererably C12 to C18, alkyl 32 esters of a C3 to C8, preferably C3 to C5, mono- or 33 dicarboxylic, monoethylenically unsaturated acid. V.I.
34 polymers of this ester based type are well-known and are usually made by free radical initiation, e.g. using a 36 peroxide in a solvent.

2~3 1 Such esters from which the polymer is derived include:
2 alkyl acrylate; alkyl methacrylate; dialkyl fumarate; and 3 dialkyl itaconate.
4 The most common of these V.I. improvers are polymers of acrylic esters represented by the formula R7 (5) 6 CH2 = c - COOR8 7 wherein R7 represents hydrogen or methyl and R8 represents 8 an oil-s~lubilizing group, especially an alkyl group of 8 9 to 24 carbon atoms. The alkyl group may be essentially straight chain and preferably contains 12 to 18 carbon atoms 11 although methyl and ethyl branching can be tolerated.
12 Representative polyacrylic and polymethacrylic esters that 13 promote oil solubility comprise octyl, decyl, isodecyl, 14 dodecyl, isododecyl, myristyl, cetyl, stearyl, eicoysyl and tetracosyl polyacrylates and polymethacrylates. The 16 term "acrylic ester" in this invention includes both 17 acrylates and methacrylates. Mixtures of both alkyl 18 acrylates and alkyl methacrylates may be used as well as 19 their partial esters.
Lower alkyl acrylic esters, here meaning esters 21 having alkyl groups smaller than 8 carbon atoms and de-22 rived from acrylic or methacrylic acid, are of particular 23 interest, because in general they possess polymerizing 24 characteristics similar to the acrylic esters which supply oil-solubility. Presence of small alkyl groups in co-26 polymers may help improve the property of viscosity index.
27 Typical lower acrylic esters are methyl, ethyl, propyl, 28 butyl, amyl, and hexyl acrylates and methacrylates. These 29 lower alkyl acrylic esters may be employed in amounts rang-ing from 0 to 25 mole %.
31 Ia addition to the one or more of the above vinyl 32 mono- and dicarboxylic esters processing oil-solubilizing 33 groups and the aforementioned lower alkyl acrylic esters, 1 the~e ma~ be use~ 'o for~ the backbone, in minor a~oun~s 2 one or more other miscellaneous free-radical polymer-:3 izable, monoethylenically unsaturated com~ounds , parti-4 cularly monovinylidene compounds, i.e., those having 5 one vinyl group in its structure; for example, vinyl 6 acetate, styrene and alkyl styrenes, vinyl alkyl ethers -7 which are represented by vinyl butyl ether, vinyl dodecyl 8 ether and vinyl octadecyl ether.
g In addition, nitrogen-containing monomers can be co-polymerized with the foregoing monomers, said nitrogen-11 containing monomers include those represented by the 12 formula:

13 Rg - C = C - H (6, Rl o Rll 14 wherein Rlo and Rll can be hydrogen and/or al~yl radicals and Rg is a 5- or 6-membered heterocyclic nitrogen-con-16 taining ring and which contains one or more substituent 17 hydrocarbon groups. In the above formula, the vinyl 18 radical can be attached to the nitrogen or to a carbon 19 atom in the radical Rg. Examples of such vinyl derivatives include 2-vinylpyridine, 4-vinylpyridine, 2-methyl-5-21 vinylpyridine, 2-ethyl-5-vinylpyridine, 4-methyl-5-vinyl-22 pyridine, N-vinylpyrrolidone, 4-vinylpyrrolidone and the 23 like.
24 Other monomers that can be included are the un-sa~urated amides such as those of the formula:

R12 (7) 26 CH2 = C'"' \ CoNHR13 27 wherein R12 is hydrogen or methyl, and R13 is hydrogen or 28 an alkyl radical having up to about 24 carbon atoms. Such 29 amides are obtained by reacting acrylic acid or a low molecular weight acrylic ester with an amine such as butyl-2;~

l amine, hexylamine, tetrapropylene, amine, cetylamine and 2 tertiary-alkyl primary amines. The tertiary-alkyl primary 3 amines referred to conform to the characterizin~ structure c (8) C

wherein a tertiary carbon atom, i.e., one devoid of hydro-6 gen atoms is bonded to a primary amino radical, i.e., 7 -NH2. ~uch tertiary-alkyl primary amines should contain 8 at least about 6 and generally not more than about 24 car-g bon atoms in the tertiary-alkyl substituent. In most in-stances, the tertiary-alkyl substituent will contain from ll about 10 to about 24 carbon atoms. Specific examples of 12 tertiary-alkyl primary amines useful for thepurposes of 13 this invention include tertiary-octyl primary amine, tert-14 iary-decyl primary amine and tertiary-hexadecyl primary amine, tertiary-eicosyl primary amine and tertiary-tria-16 contyl primary amine. It is not necessary to use a single 17 tertiary-alkyl primary amine; in fact, it i8 generally 18 more convenient to use a commercial mixture of such amines 19 wherein the tert~ary-alkyl substituent contains from about 10 to about 24 carbon atoms. A typical mixture of such 21 commercial tertiary-alkyl primary amines, for example, 22 consists of tertiary-alkyl primary amines containing from 23 about 12 to about 14 carbon atoms.
24 Still other monomers that can be included are amines and mixed amides-esters of the vinyl monocarboxylic 26 and dicarboxylic acids earlier referenced herein. These 27 monomers and the earlier discussed lower alkylacrylic 28 esters, monovinylidene compounds, nitrogen-containing 29 monomers and unsaturated amides may be individually or collec-tively employed in total amounts ranging from 0 to 25 mole 31 percent.

~.lt;S~2~;~

1 ~lkvlene Polvethers 2 These polyethers are the products of polymerization 3 or telomerization of cyclic oxides containing from two to 4 eight carbon atoms and having a ring of one oxygen atom and 5 2 or 3 carbon atoms thus conforming to the structural formula 8 ~ ~cb2) ~ Q
10 wherein R5 is an alkyl radical containing from 2 to 18 carbons 11 and z is O or 1 (see U.S. 3,634,244) and Q provides a (Mw) 12 ranging from 104 to 107.
13 Representative of another polyether is a polyoxyal-14 kylene glycol diether having the general formula l7 [RO (CH2 C~O)a(CH2 - C~O)b(CH - CHO)c]2CH2 18 wherein R is a hydrocarbon radical. a+b+c is an interger of 1~ 5-100 and a or b+c be O but a, b and c are not O at the same 20 time.
21 Production is by random or block polymerization of 22 an alcohol of Cl_24OH with propylene oxide or butylene oxide 23 then conversion to a sodium salt and then etherification by 24 means of dihalomethane.
25 Silicones 26 This includes a large group of organosiloxane poly-27 mers based on a structure consisting of alternate silicon and 28 oxygen atoms with various organic radicals attached to the 29 silicon. Silicone polymers can form flexible ring-like struc-30 tures which allow for scission of the first bond resulting in 31 a compensating increase in intrinsic viscosity even though 32 the polymer suffers mechanical shear degradation.

1 Molecular Weight Distribution (MWD) and Topolo~y 2 MWD and topological variations can be produced in 3 polymers of the chemical repeat unit types discussed above.
The variety of polymers produced for a given repeat unit will be governed partially by the catalyst type and kinetics 6 which are active for that unit.
7 Those catalysts and monomers which are ~haracterized 8 as "living" polymerizations may be used to make narrow g (Poisson) distribution (MzMz+l ~ 1) polymers- Further-11 w 12 more, the topological variations of rings, loops, star 13 and comb branched as well as random branched polymers may 14 be formed by appropriate utilization of multifunctional initiators and terminating agents. These are most often 16 anionic polymerizations.
17 Appropriate use of cationic catalysis can be used 18 to prepare saturated hydrocarbon polymers of most probable 19 molecular weight distribution tMZMz+l ~ 3) and with ~ 2 21 Mw 22 appropriate multifunctional initiators for star, graft 23 or randomly branched polymers.
24 Olefin metathesis reaction polymerizations may be used to prepare blends of rings and linear polymers.
26 Ziegler catalysts are appropriate for randomly 27 branched and loop containino polymers.
28 Siloxane ring-chain equilibrium may be used, includ-29 ing copolymers of siloxane and links with other monomers.
Reactor design, e.g. continuous stirred tanks, plug 31 flow or staged stirred tanks may be used to modify MWD
32 during initial polymerization.
33 The above polymers may be altered in their molecular 34 topoloay and molecular weight distribution by a number of chemical or mechanical/chemical reactions conducted on the 36 polymers. These include graft polymerization reactions, 1 inter- and intramolecular crosslinking reactions, chain 2 cleavaqe reactions and combinations of these reactions.
3 Terminally functional polymers may be coupled into rings 4 or branched structures. The reactions may be carried out in solution or in the bulk. Dilute solution will tend to 6 maximize intramolecular reactions, e.g. crosslinking of 7 polymer chains in solution will lead to loops and rings with-8 in the chain.
9 Lubricating Base Stock This invention is applicable to the improvement of 11 the performance of lubricating oil base stoc~s which have 12 been compounded with a V.I. additive and if desired with 13 various other oil additives including ashless dispersants 14 such as the reaction product of polyisobutenyl succinic anhydride with tetraethylene pentamine, detergent type 16 additives such as barium nonyl phenol sulfide, calcium 17 petroleum sulfonate, nickel oleate, antioxidants such as 18 a phenolic antioxidants, extreme pressure additive such as 19 a zinc dialkyl dithiophosphate, antirust agents, etc.
Base stocks for the preparations of lubricating oils 21 can be prepared from vacuum distillation fractions or 22 residues of the vacuum distillation of crude mineral oils.
23 These oils can also be prepared by hydrocracking mineral 24 oils and subsequently hydrogenating the products with the object of increasing their oxidative stability.
26 The lubricating oils to which the polymeric solutions 27 of the invention can be added include not only mineral 28 lubricating oils but also synthetic oils. The nonhydro-29 carbon synthetic oils include dibasic acid esters such as di-2-ethyl-hexyl sebacate, carbonate esters, phosphate 31 esters, halogenated hydrocarbons, polysilicones, poly-32 glycols, glycol esters such as C13 Oxo acid diesters of 33 tetraethylene glycol, etc.
34 Measurement of Compliance Both viscosity and compliance are conveniently 36 measured by a variety of equivalent techniques such as cone and plate rheometry as described in K. Walters "Rheometry"
Wiley NY 1975 p 60ff. Commercial equipment such as the Rheometrics* Mechanical Spectrometer (Rheometrics Inc., Union, NJ) can be employed. For each polymer of a particular repeat unit type and molecular weight Mw, when dissolved in the lubricating fluid at concentration, c, there will be a value of Je Fluids are viscosity modified to produce a given vis-cosity ~. This requires that the product of concentration c and intrinsic viscosity, t~ , for the polymer be a prescribed value. [~ depends on molecular weight and topology. For fixed c and Ln~ there will be a value of Je . For linear polymers this value will have a minimum value if UzM +l is Mw one, i.e. all molecules have the same molecular weight. For polymers with a MWD, Je is increased as described by MzMz+l .
M-w2 Shear stability decreases as this quantity increases, and is generally unsatisfactory when it reaches 10; for this reason, this value should be between 1 and 10, preferably 1-5 and optimally 1-3.
As previously noted Je can be measured or estimated theoretically. By theory, for a linear polymer (Rouse Model) J = 0.4 M ~ ~

Thus, for a fluid at 23 C. with c = 1 gm/100 ml and ~c=
2~s' Je = 4 x 10 10 M cm2/dyne. This relationship is in-dependent of polymer repeat unit type. Due to differences in the dependence of n on M, solutions formulated from different polymer type will have different compliances and it is not possible to specify a single value encompassing all polymer classes. It is apparent that for given chemical stability, polymers which have high capacity to * Trade Mark ....

;*ZZ3 l thicken oil for a given molecular weight will be those 2 that mechanically are most stable. Such properties are 3 attainable by having low molecular weight per backbone 4 bond, good thermodynamic interaction of polymer with the modified fluid or a stiff polymer chain as caused by short 6 range intramolecular interactions, 7 The following examples demonstrate this invention.

g In this Example, it is shown that JeR for solutions of nearly monodisperse linear and four-arm star branched 11 polybutadienes follow the relationship JcRT no2 12 JO = e ~no-n )2 13 with JeR given as calculated in the J.S. Ham reference 14 cited, i.e. that the compliance and thus the normal stres-ses in the solution of the branched polymer at the 16 same n are lower and furthermore that the susceptibility 17 of the branched polymer to sonic degradation is less.
18 Four polybutadiene samples were purchased from 19 L.J. Fetters of the University of Akron. These were pre-pared by standard anionic living polymerization techniques.
21 They were characterized by gel permeation chromatography 22 and membrane osmometry as shown in Table I. MzMz+l is less 23 ~ 2 24 w than 1.4 and the polymers are treated as being monodisperse.

27 PRIMOL (a) SOLUTIONS
28 c g/102s O
2g SamDleType M solution no/ns ~e~
ALinear 2.5 x 10' .74 1.84 .40 6t ~Lr~dc~a~K 40ra~
31 (a) Primol is~white mineral oil.

~i l t;~23 TABLE I (continued) 2 P:RIMOL (a) SOLUTIONS
3 c s/102g JO
4 Sam~le ~Y2~ Msolution ~ eR
5 B Linear 1.5 x 10 1.09 1.96 .44 C 4-arm star3.6 x 10 .77 1.75 .24 D 4-arm star2.1 x 10' 1.06 1.72 .22 8 (a) Primol is white mineral lubricating oil.
9 The molecular weigllts of the polymers were chosen so that solutions could be formulated to approximately the 11 same concentration and viscosity. Solutions were prepared 12 in a white mineral oil, Primol, [containing .5% butylated 13 hydroxytoluene (BHT)]to the concentrations shown in Table 14 I. These solutions were investigated by W. Philippoff using glass capillary viscometers and flow birefringence.
16 The latter technique can be used to measure compliances.
17 Results of these experiments were reported (Bulletin, Soc.
18 of Rheology, Oct. 1978), In Table I are reported the 19 values obtained for JeR which are in essential agreement with the theoretical estimates of .4 and .18 (J.S. Ham.
21 J. Chem. Phy~., 26, 625 (1957)). Thus it is experimentally 22 shown that polymer solutions in this [n]c range yield 23 results in reasonable agreement with theory.
24 These solutions were sonically degraded by procedure ASTM D2603 (10 minutes at .8 Amp and 40C.). Such a 26 technique is known to correlate with in-service oil per-27 formance. Kinematic viscosities of the solutions measured 28 at 210F. were measured before and after sonication and 29 the viscosity loss is calculated as follows:
(nooriginal - n recorded) ~ loo/nooriginal. If this 31 quantity is correlated with the molecular weight of the 32 polymers, it is found that the branched polymers degrade 33 less at a given molecular weight as shown in Table II.

;2 viscositv Normal Stress in Dy~es/cm 3 Polymer Loss,% at Shear Stress of 10 dynes/~-;r 4 A 9.4 247 B 2.3 110 6 C 5.8 180 7 D 1.4 63 8 Instead of correlatina degradation with molecular g weights, use of the normal stresses e,:hihited by the solu-tions at a given shear-stress to calculate maximum stored 11 energy per bond results in a correlation which is inde-12 pendent of molecular topology.

14 In this Example, it is shown that a similar resis-tance to degradation exists for another topological class 16 of polymers that of comb branched polystyrenes. Linear 17 polystyrene samples were purchased from Pressure Chemicals 18 Co. (Smallman St., Pittsburgh, PA) Duke Scientific 19 (California) and branched polystyrenes were obtained from Roovers. Characteristics of the linear polymers are sup-21 plied by the manufacturer whereas those for the comb 22 branched polymer have been published (Macromolecules 11, 23 365 (1978)) and are given in Table III. Solutions were 24 prepared in 1,2,4-trichlorobenzene, containing .05~ inhi-bitor (BHT) to the concentrations shown in Table III.

27 Polystyrene nO37.5C Visc.
28 Sample Molecular Weight Number of Branches cstokes Loss,~
29 A 9.7x104 0 1.5 3.5 B 6.7x105 0 12. 68 31 C 2.0x106 18. 82 32 D 4.1x106 0 42. 94 33 E 3~6x1,6 28 5.2 57 34 F 3.1xlO 29 7.5 68 1 The solutions were tested for viscosity loss as 2 in Example 1 (.8 amp 5 minutes 40C). As was the case in 3 Example 1 the branched polymers degrade significantly less 4 at a given molecular weight. Certain of these solutions had similar viscosities as in Example 1. If the linear and 6 branched structures which have similar viscosity-modif~ing 7 characteristics are compared, it is found that the suscepti-8 bility to degradation is similar. Thus comb polymers with 9 large numbers of branches are not as shear stable as four-arm stars, 12 In this Example, linear polymers are formulated to 13 prescribed MWD by blending polymers of known characteris-14 tics. It is shown that the criterion of MzMz+l C 10 is 16 w 17 a better measure of degradability than is Mw rMn < 8 as 18 previously taught.
19 Four linear ethylene-propylene copolymers were used whose characteristics appear in Table IV. These samples 21 were characterized by vapor phase osmometry, membrane 22 osmometry and gel permeation chromatography (GPC) with 23 on-line low angle laser light scattering (LALLS). All 24 samples had ethylene contents in the 40-50 wt.% range and were prepared by continuous flow stirred reactor processes that 26 results in a most probable distribution of molecular 27 weights to a good approximation.

29 _ - 1 - 1 [n]135C
30 Polymer Mn 2 Mw 3 Mz z+l Decalin 31 A 9.xlO 1.8xlO 2.7xlO 3.6xlO .06 32 B 2.5xlO 5.x104 7.5x104 l.x105 1.0 33 C 6.7x104 1.35x105 2.0x105 2.7x105 2.0 34 D 1.5x105 3.0x105 4.5x105 6.x105 3.5 E 3.7x105 9.10x105 1.2xlo6 1.8xlo6 8.2 36 1. Calculated ~rom distribution and Mw 1 For such a ~D when analysis is done with a GPC
2 which has an approximately linear elution volume log M
3 calibration, the peak in the light scattering chromatogram 4 corresponds to Mz. Thus the power of the technique to detect high m~lecular weight averages is apparent.
6 Blends of the polymers in Table IV were formulated 7 as shown in Table V. Solutions of these blends were 8 formulated in a lubricatmg oil-All had the same [~] = 2.
9 and thus the same thic~ening efficiency. These solutions were tested for kinematic viscosity and degraded as in 11 Example 1 with the results shown in Table V. The cal-12 culated Je for the monodisperse polymer of the same Mw and 13 repeat unit is 0.1 cm2/dyne.
14 It is apparent that the group M~Mz+l is a sensi-16 w 17 tive test of degradability and that Mw/Mn which is taught 18 in previous art fails to predict degradability in both a 19 false positive and negative fashion.
TABLE V
21 z z+lw Calculated 22 Rw2Mn ~e m2/dvne Loss 24 Control Polymer C 3 2 1.6 31.
Blend A A:C:D .06:.9:.04 3.4 11. l.BxlO 31.
26 ~lend B B:E .86:.14 55 5. 29xl9 46.
27 1. Monodisperse pol~mer would have Je=5.xlO cm2/dyne.
28 Since it has been shown that this invention is ~9 applicable to a wide range of polymer types and diverse topology, it is possible to predict the behavior of vary-31 ing comparative polymeric structures and types as illus-32 trated in the following:
33 (A) A sol~tion can be prepared from a polymer which 34 is in the form of large flexible rings. The compliance would be a smaller value than that of a linear polymer I ~ 68~2 3 ~ of the same molecular weight as calculated in Table VI.
2 The ring containing polymer would be more resistant to 3 bond breakage upon mechanical stress compared to the linear counterpart. h7hen bond rupture occurs the viscosity n Q Of ; the ring polymer-containing solution increases.
6 TA~LE VI
-7Polymer Type ~w [~] Jc/(Jc)Linear 8 A Linear l.x105 1.8 g B ring 1.37x105 1.8 .66 (B) ~ polymer solution can oe formulated to be 11 within the rangc .1 < [n]c < 5 from a blend of nolvmers of 12 type A and B of the preceding (A). When the polymer bonds 13 are broken upon mechanical degradation the viscosity of 14 the solution n would remain essentially constant due to a concurrent increase in [n ] of the ring polymer upon bond 16 breakage.
17 (C) A polymer solution can be formulated in the 18 range .1 ~n]c < 5 using a polymer that was intramolecular-19 ly crosslinked in dilute solution forming large loops and branched structures. The resulting solution would be more 21 stable to degradation than the solution of a linear poly-22 meric counterpart of the same [n] and c due to the reduced 23 compliance of the loop containing polymer.
24 (D) A polymer which contains functional groups or repeat units can be partially ionized or otherwise be 26 made particularly compatible with the fluid to be vis-27 cosity-modified resulting in a highly extended conforma-28 tion of the polymer in solution, e.g. a 1 wt.~ of sulfo-29 nated ( ~ 2% sulfonation) polystyrene in dimethyl form-amide. Such polymers are extremely effective at increasing 31 solution viscosity and thus may be used at low Mw and 32 therefore very low Je with resulting good shear stability 33 of the resulting solution.

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A polymer composition comprising a lubricating oil and an oil-soluble polydisperse polymer at a concentra-tion such that the product of the intrinsic viscosity [n]
of said polymer in said oil times the concentration c ranges from one-tenth to five, the oil composition having a com-pliance no larger than twenty times the value exhibited by a linear monodisperse polymer of the same chemical repeat structure and of the same weight average molecular weight (Mw) as said polydisperse polymer whereby said polydisperse polymeric oil composition exhibits an enhanced stability to viscosity loss when subjected to mechanical stress, and wherein said polymer is a linear polymer having a of less than 10 and/or a polymer having a topological non-linearity as evidenced by long-chain branches or large rings or loops and wherein said linear polymer and said polymer containing long-chain branches are of the class consisting of polyisobutylene, ethylene copolymers, ethylene ter- and tetrapolymers, poly(alkylated styrene), polybutadiene, and ester-based polymers.

2. The composition of claim 1 wherein said oil is a mineral lubricating oil.

3. The composition of claims 1 or 2 wherein the compliance of said oil composition is no larger than 5 times said value and said polydisperse polymer has a ?w of from 104 to 107.

4. The composition of claims 1 or 2 wherein said polydisperse polymer is present in said oil composition in an amount ranging from 0.5 to 10 weight percent, based on the total weight of said composition.

5. The composition of claim 1 wherein said polydisperse polymer is characterized by the presence of topological nonlinearity as evidenced by long-chain branches, flexible rings or loops.

6. The composition of claim 5 wherein said long-chain branches are formed by cross-linking, or are the arms of a star-branched polymer or are defined by a comb-branched polymer.

7. The composition of claim 5 wherein said polymer is characterized by rings or loops.

8. The composition of claim 6 wherein said star-branched polymer is polybutadiene having a of less than 1.4.

9. The composition of claim 6 wherein said comb-branched polymer is comb-branched polystyrene.

10. The composition of claim 1 wherein said linear or nonlinear polymer is a copolymer, terpolymer or tetrapolymer of ethylene and propylene.

11. The composition of claim 6 wherein said polymer is star-branched and the degree of branching is between 5 and 16.

12. The composition of claims 1 or 10 wherein said linear polymer has a of 1 to 5.

13. The composition of claims 1 or 10 wherein said linear polymer has a of 1 to 3.