Accordingly, the 1 H NMR spectra acquired over time of PCPA-O2, PFPA-O2 and DIPA-O2 stored at 50 °C, showed full recovery of DIPA within < 0.5 h and > 75 % recovery of PFPA and PCPA after 35 h. Moreover, the lack of signals related to potential impurities confirmed that the cycloreversion reaction was the only process happening upon thermolysis. The UV-Vis data were used to calculate the thermolysis rate constants (k, s -1 ) as well as the half-life time (t1/2) of the EPOs, shown in Table for 37,5°C. The Activation Energy (AE) for O2 release was obtained from the Arrhenius plots for each substrate (Figures S14, Figure ).