Extended Data Fig. 1: The reaction mechanism between o-nitrobenzyl alcohol (NB) groups and methacrylate groups in the presence of LAP.
a, The reaction between nitrosobenzene and LAP in methanol was confirmed by UV-vis spectroscopy. b, The PEGNB in methanol was first irradiated to give PEGNO. LAP (two equivalents) was then added, and the solution was subsequently irradiated. Alternatively, the PEGNB and LAP (two equivalents) in methanol were directly irradiated. c, The reaction between d-NB and LAP in methanol was characterized by HPLC. d, ESR spectra of the reaction products formed between d-NB and LAP (2 equivalents). The ESR signals were recorded immediately after irradiation (left) and 20 minutes later (right) to verify the formation of persistent nitroxides. e, The structural formula and LC-MS spectra of the product (the d-NB nitroxide abstracting a hydrogen). This product was formed by the reaction between d-NB (20 mM) and LAP (20 mM) in methanol under 395-nm light irradiation. f, The general structural formula and corresponding LC-MS spectra of the photo-polymerization products formed by photo-polymerization of d-NB (1 eq), 2-hydroxyethyl methacrylate (10 eq), and LAP (2 eq) in methanol solution. The n represents the polymerization degree of 2-hydroxyethyl methacrylate. We conducted these experiments to study the details of the reaction between NB groups and methacrylate in the presence of LAP. This reaction mechanism can be divided into two steps: in the first step, NB groups underwent the typical photolytic reaction and were converted to o-nitrosobenzaldehyde groups, which reacted with the LAP radicals to yield the persistent nitroxides (Extended Data Fig. 1a–e). The reaction between NB groups and LAP was thorough and occurred quickly (Extended Data Fig. 1c). In the second step, the nitroxides captured the carbon-centered radicals formed by the polymerization of methacrylate (Extended Data Fig. 1f).
