Viscosity studies on solutions of ethylene-propylene copolymers with 5
8 to 80 mol % ethylene in mineral and synthetic oils revealed that cop
olymers with 80% ethylene and slight crystallinity could give lower vi
scosities than expected on the basis of their molecular weights. This
was true for intrinsic viscosities and shear viscosities of solutions
of 1.0% copolymer. All copolymer solutions were lower in viscosity at
about - 10-degrees-C or below than those of copolymers with 60-70% eth
ylene and no crystallinity. In the synthetic base stock, polydecene- 1
, their viscosities were also lower than expected at room temperature
and above. It is believed that this is due to structural domains invol
ving the longer ethylene sequences of the copolymer chains with 80% et
hylene.