A qualitative mathematical model on the oscillating behavior of reactive extrusion is presented. Through the introduction of stagnant volume build up in the die as a result of the on going reactive extrusion process, a variable time dependent die rest. stance emerges. A differential equation for the waxing and waning of stagnant volume in the die is developed. This equation is able to give oscillating behavior for certain extruder parameters and viscosity when coupled to an existing dynamic model of the fully-filled length. The effects of reaction rate, rotational speed, feed rate, die resistance and degree-of-fill are studied.