Photolabile SI-PET-RAFT Initiators for Wavelength-Selective Grafting and De-grafting of Polymer Brushes

Polymer brushes offer a wide array of applications in surface modification. While recent advances have made these chemistries more user-friendly, scientific questions about fundamental polymer properties often remain unanswered. For example, copolymer brush composition, chain end fidelity, and dispersity often remain prohibitively challenging to characterize. This conundrum produces a need for chemically precise pathways to evaluate polymer brushes. To this end, this contribution describes the synthesis of an o-nitrobenzyl-based photolabile initiator for surface-initiated reversible deactivation radical polymerization. The product can be immobilized on surfaces, enable growth of polymer brushes under visible light, and be cleaved under ultraviolet (UV) irradiation. Wavelength selectivity is confirmed using a combination of ellipsometry, tensiometry, and X-ray photoelectron spectroscopy, and patterning experiments indicate good spatial control over photocleaving. Finally, nuclear magnetic resonance spectroscopy indicates visibility of characteristic peaks for both chain ends after degrafting of the polymer brush.