The characteristics of thermal degradation, peroxide induced degradation, and maleation of polypropylene have been modeled in a modular intermeshing twin screw extruder for a range of screw configurations and screw speeds. The models use the Akro-co-Twin Screw(R) formulation and account for starvation and fully filled pressurized regions including the effects of viscosity reduction along the screw axis by both degradation and viscous heating. The results are compared with experiments.