Amorphous and low crystallinity polypropylenes were produced by reactive processing of commercial isotactic polypropylenes in the presence of a peroxide (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) and N-bromosuccinimide. Characterization of the modified polypropylene microstructures using C-13 NMR spectroscopy revealed that crystallinity loss is correlated with the epimerization of numerous methynes randomly along the polymer backbone, leading to decreasing isotacticities ([mmmm]) and average isotactic block lengths. Moreover, degradation usually induced by peroxide was shown to be comparatively limited in additional presence of N-bromosuccinimide. This fast and easy process therefore allows the production of polypropylene plastomers and elastomers with controlled and homogeneous crystallinities and isotacticities, and relatively low molecular weight distributions. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4505-4518, 2009