The in situ “grafting from” approach for the synthesis of polymer brushes on upconversion nanoparticles via NIR-mediated RAFT polymerization

We report the first example of in situ polymer brush growth on the surface of upconversion nanoparticles (UCNPs) in a one-pot near-infrared (NIR) light mediated reversible addition–fragmentation chain transfer (RAFT) polymerization. In the process of polymerization, the surface growth of polymer brushes was realized through an efficient in situ ligand exchange between a photo-activated chain transfer agent (CTA) and the ligand groups on the surface of UCNPs. BF₄⁻ was found to be the most efficient ligand in comparison with oleic acid and pyridine. The 980 nm NIR-mediated RAFT polymerization exhibits good temporal control with a low dispersity (M_w/M_n < 1.30), and the thickness of the polymer brushes can be easily adjusted by changing the polymer molecular weight and light exposure time. Moreover, the growth of polymer brushes can proceed even if there is a barrier (e.g. chicken skin) outside the reactor due to the excellent penetration ability of the NIR light.