| 摘要 |
PROBLEM TO BE SOLVED: To provide a viscosity index improver having excellent viscosity index improving effect. SOLUTION: The viscosity index improver is composed of a copolymer (A) containing a monomer (a) satisfying the conditions (I) and (II) and expressed by general formula (1) as an essential constituent monomer. In the formula, R<SP>1</SP>is H or methyl; X is a 2-4C alkylene; (n) is an integer of 0-20; and R<SP>2</SP>is a 16-36C branched alkyl group. The condition (I): the homopolymer of the monomer (a) has a solubility parameter of 8.6-8.9 and a crystallization initiation temperature of≤5°C and the condition (II): the copolymer (A) has a weight- average molecular weight of 5,000-2,000,000, a solubility parameter of 8.6-9.5, a crystallization initiation temperature of≤-15°C and a steric hindrance factor F defined by formula (2) F=4X+Y of≥0 and <15 (X is the total number of the 6th atoms and Y is the total number of the 7th atoms counted from the main chain and positioned on branched chains). COPYRIGHT: (C)2004,JPO |
