ABSTRACT
In lubricated contacts, oil film thickness is a critical design feature of a lubricant and it is controlled, in large part, by viscosity. Should viscosity drop below a critical value, opposite surfaces can begin to come into contact resulting in premature wear and fatigue damage. High molecular weight polymers, known as viscosity modifiers (VM) or viscosity improvers (VI), are added to lubricating oils to boost viscosity at high temperatures while minimizing thickening contribution at low temperatures. Viscosity increase is proportional to both VM concentration and molecular weight. To preserve lubricant film thickness between the moving surfaces over time, it is desirable to minimize molecular weight degradation of the polymer additive (see Chapter 4).
