Isotactic polypropylene (iPP) is a thermoplastic with several desirable properties as it can be modified by additives and processing, making it one of the most versatile and popular polymers. In this context, we present a detailed study of morphological and mechanical properties of non-additivated iPP produced by reactive processing, mainly concerning the effect of controlled radicalar degradation on polymer structure in molten and solid states. Melt rheology and size exclusion chromatography analyses evidenced the reduction on viscosity and moduli in dependence of molecular weight by the addition of commercial peroxide. The behavior in solid state showed that smaller chains of degraded iPP at high temperatures exhibited greater mobility resulting in a more viscous response upon a mechanical loading. Moreover, beta-form crystals were suppressed by molecular weight reduction as suggested by X-ray diffraction. This finding suggests that smaller chains have higher mobility, and consequently are less susceptible to shear deformations during processing.