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US6110880A - Polyolefin block copolymer viscosity modifier- Google Patents US6110880A - Polyolefin block copolymer viscosity modifier- Google Patents Polyolefin block copolymer viscosity modifierInfo Publication number US6110880A US6110880A US08/881,171 US88117197A US6110880A US 6110880 A US6110880 A US 6110880A US 88117197 A US88117197 A US 88117197A US 6110880 A US6110880 A US 6110880A Authority US United States Prior art keywords wt block viscosity modifier polymer ethylene Prior art date 1997-06-24 Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.) Expired - Lifetime Application number US08/881,171 Inventor Gary William VerStrate Charles Cozewith Thomas John Pacansky William Myers Davis Pratima Rangarajan Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)ExxonMobil Chemical Patents IncOriginal Assignee ExxonMobil Chemical Patents Inc Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.) 1997-06-24 Filing date 1997-06-24 Publication date 2000-06-24 Application filed by ExxonMobil Chemical Patents Inc filed Critical ExxonMobil Chemical Patents Inc 1997-06-24 Priority to US08/881,171 priority Critical patent/US6110880A/en 1997-12-04 Assigned to EXXON CHEMICAL PATENTS, INC. Reassignment EXXON CHEMICAL PATENTS, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS).
The present invention relates to novel block copolymers particularly useful as oil viscosity modifiers that display an improved balance of thickening efficiency and shear stability. These block copolymers comprise blocks of substantially pure polyethylene, and blocks of copolymers containing ethylene and at least one other α-olefin.
Lubricating oils containing the unique viscosity modifiers and the process for producing the block copolymers are also provided. BACKGROUND OF THE INVENTIONEthylene-propylene copolymers are important commercial products and are widely used as viscosity modifiers (VM) in lubricating oils. A motor oil should not be too viscous at low temperatures so as to avoid serious frictional losses, facilitate cold starting, and provide free oil circulation at engine start-up. On the other hand, too thin an oil at high temperature will cause excessive engine wear and oil consumption.
It is most desirable to employ a lubricating oil which experiences little or no viscosity change in response to changes in oil temperature.Over the last thirty years, efforts have been made to improve the thickening efficiency (TE) and shear stability (SSI) performance of lubricating oil viscosity modifiers. The thickening efficiency is a measure of the thickening power of the polymer, and is defined as:TE=(2/C) ln ((kv of polymer+oil)/(kv of oil))/ln (2)wherein kv is the kinematic viscosity at 100° C., C is the concentration in grams/100 grams of solution, and the log is consistently either natural or base 10.The TE of a viscosity modifier depends somewhat on the particular base oil and other formulating components in the base oil, as well as the polymer concentration. For the purposes of this application, the oil is designated to be a solvent 100N, such as FTN135 (a product of Exxon Chemicals) containing no components other than the viscosity modifier of the present invention, with a polymer concentration sufficient to double the viscosity of the base oil at 100° C.The shear stability is a measure of how well the polymer resists degradation due to the mechanical stresses applied by an engine. The SAE-ASTM-DIN test used to measure this tendency for degradation is the Kurt Orbahn Shear Stability Test (ASTM D3945-86, hereinafter 'KO SSI').Previous efforts to simultaneously improve TE and SSI of ethylene, α-olefin copolymers have involved increasing the ethylene content of the polymer and narrowing the molecular weight distribution (MWD). The upper limit for ethylene content is determined by the requirement that the dilute polymer has to be soluble, or remain in suspension with no macroscopic gellation,in oil down to a temperature of at least -40° C.
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Thus, pure polyethylene is beyond the limit. For simple statistical copolymers, the average ethylene content cannot be made higher than about 76 wt.% (determined in accordance with ASTM D3900-95) without causing the copolymer to become insoluble in oil. At these levels, however, pour point problems are encountered. However, it has been demonstrated that even when the ethylene content exceeds only about 61 wt.%, many of the methylene sequences in the viscosity modifier are of a length which allows them to co-crystallize with paraffin waxes in the oil, thereby leading to undesirably high viscosities and gellation of the oil. Typically, conventional ethylene, α-olefin viscosity modifiers that can be employed to formulate lubricating oils having pour points of -30° C.
Or below are restricted to an average ethylene content of no greater than about 56 wt.%, unless the molecules possess an intramolecular compositional distribution (CD) tailored to improve such properties, as is disclosed in U.S. 4,900,461.The present inventors have developed a unique viscosity modifier, formed of a block copolymer comprising a first block of substantially pure polyethylene and a second block of a copolymer of ethylene and another α-olefin; such that the block copolymer has a high average ethylene content so as to provide an excellent balance of thickening efficiency and shear stability.
More importantly, however, is the fact that this unique block copolymer viscosity modifier of the present invention possesses unusual solubility characteristics, agglomerating above wax crystallization temperatures, thereby preventing its co-crystallizing with paraffin waxes in the oil and the undesirable formation of high viscosities or gellation of the oil. Furthermore, the present inventors have discovered that when blocks of substantially pure ethylene are used as the A block of a block copolymer, the ethylene sequences in the B block, even in the 50 wt.% range of B block ethylene content, will not crystallize with paraffins and cause high oil viscosity at temperatures below about 0° C.
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