Thanks for your responses and interest in Viscosity Modifiers.
We can think of Viscosity Modifiers as falling into two categories:
2) Viscosity Index Improvers (VII's).
Thickeners increase the viscosity of a lubricant without necessarily increasing the Viscosity Index (VI). One of those thickeners is a high viscosity Bright stock, a thick Group I oil, used as thickeners in engine oils and gear lubes, but is less used today because of less Group I production, and because better and more stable thickeners are available.
Another thickener is Polyisobutene (PIB's). At low treat rates, high viscosity PIB's are often used as viscosity "adjusters" to low-viscosity base stocks. PIB popularity has decreased due to poor oxidative and mechanical stability. However, they are still used in two-stroke engine oils, gear oils, and hydraulic fluids.
Viscosity Index Improvers (VII's) will have a larger effect on solution (bulk) viscosity at higher temperatures than at lower temperatures, thereby increasing the Viscosity Index (VI), which is the most commercially used measure of the rate of change of viscosity with temperature.
Some of the polymer VII's include Olefin Copolymers (OCP's), Polyalkyl Methacylates (PAMA's), Hydrogented Styrene-Dienes (HSD's), and PAMA-OCP polymer Blends.
Last edited by MolaKule; 06/11/19 11:19 AM.