Claims
- 1. A process for improving the viscosity index (VI) of a base oil, comprising the steps of:
- sequentially polymerizing styrene, isoprene, and a polyalkenyl coupling agent to form a star polymer having the formula (A-B).sub.n -X wherein B is a hydrogenated block of polyisoprene having a number average molecular weight (MW.sub.1) between 30,000 and 60,000, A is a block of polystyrene having a number average molecular weight (MW.sub.S) from 3,000 to 4,000, X is a nucleus of the polymerized polyalkenyl coupling agent, and n is the number of block copolymer arms in the star polymer when coupled with 2.5 or more moles of the polyalkenyl coupling agent per mole of living block copolymer molecules;
- recovering the star polymers as a solid crumb; and
- blending a VI improving amount of the star polymer crumb with a base oil.
- 2. The process of claim 1, wherein the molecular weight of the polyisoprene block is 53,400.
- 3. The process of claim 2, wherein the molecular weight of the polyisoprene block is 3,100.
- 4. The process of claim 1, wherein n is the number of arms when coupled with 3 moles of divinylbenzene per mole of living block copolymer molecules.
- 5. The process of claim 1, wherein the combination of the base oil and the star polymer is a 10w-40 multigrade lubricating oil composition.
- 6. The process of claim 1 wherein the polyisoprene blocks are at least 98% hydrogenated.
Parent Case Info
This is a division of application Ser. No. 08/083,857, filed Jun. 25, 1993, now abandoned which is a continuation of application Ser. No. 07/790,610, filed Nov. 8, 1991, now abandoned.
US Referenced Citations (7)
Foreign Referenced Citations (1)
Number |
Date |
Country |
716645 |
Aug 1965 |
CAX |
Divisions (1)
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Number |
Date |
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Parent |
083857 |
Jun 1993 |
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Continuations (1)
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Number |
Date |
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790610 |
Nov 1991 |
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