Patent ID: 6034042
Filing Date: 2000-03-07
Classification: C08F,C08L,C10M,C10N

Abstract:
A solid polymeric viscosity index (VI) improver, comprising a star polymer structure selected from the group consisting of(I) (S-EP-EB-EP').sub.n -X(II) (EP-S-EB-EP').sub.n -X(III) (EP-EB-S-EP').sub.n -XwhereinEP is an outer hydrogenated block of polyisoprene having a number average molecular weight (MW.sub.1) between 6,500 and 85,000 before hydrogenation;EB is a hydrogenated block of polybutadiene having a number average molecular weight (MW.sub.2) between 1,500 and 15,000 before hydrogenation and having at least 85% 1,4-polymerization;EP' is an inner hydrogenated block of polyisoprene having a number average molecular weight (MW.sub.3) between 1,500 and 55,000 before hydrogenation;S is a block of polystyrene having a number average molecular weight (MW.sub.s) of 1,000 to 4,000 when the S block is external (I) and 2,000 to 15,000 when the S block is internal (II or III);wherein the star polymer structure comprises from 3% to 15% by weight of the butadiene, the ratio of MW.sub.1 /MW.sub.3 is from 0.75:1 to 7.5:1, X is a nucleus of a polyalkenyl coupling agent, and n is the number of block copolymer arms in the star polymer when coupled with 2 or more moles of the polyalkenyl coupling agent per mole of living block copolymer molecules.