To identify the monomer composition of the species detected by SEC-UV and elucidate possible chemical composition changes, the degradation products-insoluble in the reaction media-were solubilized in THF and analyzed by SEC-UV/ESI-MS. While UV detection provided information on the entire polymer molecular weight distribution, as shown in Figure , MS hyphenation enabled the identification of the chemical composition of a wide range of oligomers (up to 5300 Da). Due to health hazards and ESI compatibility, we adopted THF as the solvent for the SEC-MS analysis. Similar profiles were observed between SEC in THF and HFIP for this polymer. It has to be noted that MS analysis cannot be considered quantitative as the analysis reflect chemical composition only of the low MW components of the polymers, and as different chemical composition may have different MS ionization efficiency. However, this technique is applied to qualitative capture changes in chemical composition. A systematic data analysis approach was applied to the MS spectra recorded during SEC separation. For clarity, only a fraction of the mass spectra is depicted in Figure (signals sum from 8 to 9 min of SEC elution) and only the results for the samples treated with LCC WCCG and the negative control are reported. Details of the assignments as well as data for PES2 treated with Tc_Cut2NV WCCG are provided in the SI (Fig. and S20; Table ). Results with Tc_Cut2NV are not discussed as we observed a lower level of hydrolysis with this enzyme.