Structural modifications of a commercial polypropylene (PP) sample are studied by IR spectroscopy. Aging this sample under an ambient atmosphere with or without the presence of ambient light shows the oxidation process to be the most predominant. Spectral analysis reveals that the commercial sample is isotactic and also indicates that, for the new sample, oxygen establishes single bonds with carbon. However, through the aging process, spectral changes essentially occur in the regions of similar to 3400, similar to 1712, and 1170 cm(-1) which correspond to hydroxyl and/or hydroperoxide groups, a carbonyl group, and C-O, respectively. The deconvolution of the bands corresponding to a carbonyl group reveals the presence of a complicated mixture of oxidation products: aldehydes, ketones, esters, acids, peresters, and peracids. Spectral analysis also shows that the most favorable site for oxidation is at the methylene group.