| abstract |
(57) [Problem] To provide a viscosity index improver that further lowers the low-temperature viscosity than a conventional polymethacrylate-based viscosity index improver. SOLUTION: Propylene oxide 29 is added to 1.8 parts of water. 0 parts by addition polymerization, and then butylene oxide 2016 Part of an oil-soluble polyalkylene ether (A) obtained by addition polymerization of (A) having a number average molecular weight of 18,80. 0, a viscosity index improver having a solubility parameter of 8.67, a crystallization onset temperature of -40 ° C or lower by a differential scanning calorimeter, and a steric hindrance factor of 3.1. |