Viscosity modifer polymers

A composition comprising (a) oil;

• and (b) having from 0.01 to 50 wt. percent based on the total weight of the composition of block copolymer comprising monomeric units derived from butadiene and at least one conjugated diene comonomer represented by the formula ##STR29## wherein R.sup.1 is a C.sub.1 to about C.sub.8 alkyl radical and R.sup.2 is hydrogen or C.sub.1 to about C.sub.8 alkyl radical, the copolymer being hydrogenated and comprising at least 10 percent by weight of at least one crystallizable segment comprised of at least eleven methylene units in sequences sufficiently long to impart crystallinity to said segment and having an average 1,4-polybutadiene content of at least about 20 mole percent and more than one low crystallinity segment having a degree of crystallinity of less than about 0.2 percent at 23.degree. C. comprised of methylene units and substituted methylene units and having an average 1,4-polybutadiene content less than about 20 mole percent.