A mathematical model for the reactive extrusion of methyl methacrylate (MMA) is presented. Key variables, such as pressure, temperature, residence time, filling ratio, number-average, and weight-average molecular weights (M-n and M-w) along the extruder length can be calculated using the model. The flow in the extruder is modeled using a simplified approach; however, this approach is versatile enough to include any screw profile, such as right-handed and left-handed elements, and kneading disks. A polymerization kinetic model that considers a mixture ("cocktail") of initiators is coupled to the flow equations. An effective model for the auto-acceleration effect is used. Second-order thermal self-initiation of MMA is considered in the reaction mechanism. The model can be easily performed on a personal computer, and a wide range of process conditions can be modeled, because of its flexibility.