| abstract |
The invention provides cyclone-finishable polymeric viscosity index improvers, produced by the process comprising the steps of:n (a) preparing by anionic polymerisation a copolymer having a number average molecular weight in the range from 125,000 to 275,000, an isoprene content from 90 to 98 per cent by weight, wherein at least 85% of the isoprene units have a 1,4-configuration, and a monoalkenyl aromatic hydrocarbon content from 10 to 2 per cent by weight; and comprising a block structue A-A/B wherein A is a homopolymer block of the isoprene and A/B is a copolymer block of the isoprene and the monoalkenyl aromatic hydrocarbon, the homopolymer block A comprising at least 60% of the copolymer by weight; and (b) hydrogenating at least 95% of the isoprene and at least 5% of the monoalkenyl aromatic hydrocarbon; a process for their preparation; and oil compositions containing them. |