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. However, there are limitations to doing accurate mass analysis of high molecular weight polymers. For example, as the polymer molecular weight increases, the ionization efficiency, detection sensitivity, and ratio of monoisotopic ions used for accurate mass analysis all decrease. One way to address this is to use an “on-plate alkaline degradation” method  that was previously published in which high molecular weight polyester or polycarbonate are partially hydrolyzed by an alkaline reagent to form smaller oligomers that can then be analyzed by high-resolution MALDI-TOFMS. This degradation into oligomers is not only advantageous for accurate mass analysis but also for structural analysis by using tandem time-of-flight mass spectrometry (TOF-TOF). In this report, we investigated the structural analysis of the polyethylene-terephthalate (PET) polymer exposed to the on-plate alkaline degradation method by using the JMS-S3000 'SpiralTOFTM-plus' with TOF-TOF option. The SpiralTOFTM-plus uses an ultra-high resolution TOF for MS1 which allows monoisotopic precursor selection and a reflectron TOF for MS2 to analyze the product ion spectra produced from high energy collisional induced dissociation (HE-CID).