Thanks to all who responded and since this question was open to ALL, I thought there might be more responses.
Congratulations to rollinpete who supplied all three answers.
Thickening efficiency, the viscosity-temperature relationship, and shear stability are all Key features of Viscosity Index Improvers.
No one VI Improver can deliver optimum performance in all three areas, which is why new VII's have been developed which enhance overall polymer performance.
For example, the PAMA-OCP VII chemically "grafts" PAMA molecules onto the OCP backbones to improve the performance in all three areas.
Last edited by MolaKule; 06/14/19 04:17 PM.