| 摘要 |
A polymeric blend particularly useful as a VI improver, which polymeric blend comprises a selectively hydrogenated asymmetric radial polymer comprising a plurality of polymeric arms containing hydrogenated conjugated diolefin monomer units and at least one block copolymer arm comprising a single polymeric block containing predominantly monoalkenyl aromatic hydrocarbon monomer units and a single polymeric block containing predominantly hydrogenated conjugated diolefin monomer units and a selectively hydrogenated linear diblock copolymer containing a single polymeric block containing principally monoalkenyl aromatic hydrocarbon monomer units and a single polymeric block containing predominantly hydrogenated conjugated diolefin monomer units. Both polymers in the blend will be selectively hydrogenated so as to convert (saturate) at least 95% of the ethylenic unsaturation initially contained therein. When used as a VI improver, the polymeric blend unexpectedly improves the thickening efficiency over and above the thickening efficiency that would be expected from a consideration of the individual contribution made by each of the polymers separately. The monoalkenyl aromatic hydrocarbon polymer blocks in both polymers is preferably styrene and the conjugated diolefin in both polymers is preferably isoprene. Preferably, both polymers are selectively hydrogenated so as to convert (saturate) at least 99% of the ethylenic unsaturation initially contained therein.
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