Matrix assisted laser desorption/ionization (MALDI) mass spectrometry is a powerful tool for the analysis of synthetic polymers. This technique, when combined with a high-resolution time-of-flight mass spectrometer, can be used to identify differences in monomer, polymer end groups, and their molecular weight distributions. The molecular weight distribution is often expressed as number average molecular weight (M n ), weight average molecular weight (M w ), and dispersity (D). More recently, MALDI mass spectrometry imaging (MALDI-MSI) has been used to visualize the locations of compounds on sample surfaces. However, this technique has not been widely used for polymer analysis. Previously in MSTips 306, we reported combining M n , M w and D visualization methods with Kendrick mass defect (KMD) analysis. In this report, we have applied this combined method to analyze a polyethylene terephthalate (PET) that was degraded by ultraviolet (UV) irradiation.