AbstractThis work brings a new insight into the structural transformation and stabilization of polydopamine (PDA) surfaces induced by thermal treatment. Taking advantage of the isotopic enrichment, 15N CP/MAS NMR experiments produce significant signal enhancements for PDA, allowing detection of a range of nitrogen structural units—the reaction products of the conversion of NH3+ units of 15N‐dopamine·HCl. In addition, 1H‐15N cross‐polarization polarization‐inversion profiles measured for each of the detected 15N NMR signals and 1H‐15N FSLG HETCOR NMR spectra allow revisions and extensions to be made in a structural elucidation of PDA. Combining the NMR data thermogravimetric analyses and an FTIR analysis, several competitive processes that occur during the thermal conversion of dopamine are identified.