Surface initiated radical-promoted cationic photo-polymerization from silica nanoparticles employing a trisacylgermanium photoinitiator

Low-toxic, visible light-sensitive Ge-based photoinitiators have already been immobilized onto inorganic substrates including silicon wafers, quartz, and spherically shaped silica nanoparticles. However, these Ge-mediated grafting-from approaches are dominated by oxygen-sensitive radical pathways. In this contribution, we broaden the scope to cationic brush growth by implementing surface-initiated radical-promoted cationic photopolymerization (SI-RPCP). Chemically induced dynamic nuclear polarization (CIDNP) experiments provide direct mechanistic evidence of the electron transfer between photogenerated germyl radical and iodonium salts, yielding Ge-cation species that initiate chain growth. Under visible-light irradiation (450 nm), this approach enables the cationic polymerization of vinyl ether and epoxy monomers, forming polymer brushes on the surface of silica nanoparticles with diameters of 30 and 180 nm. The grafted polymer structures on the surface were comprehensively characterized using FTIR, solid-state NMR, XPS, SEM, and ToF-SIMS. Comparative analysis with the corresponding homopolymers confirmed the successful grafting, while thermogravimetric analysis (TGA) indicated a polymer loading of up to ∼ 40%. From the grafted mass (TGA) and the number average molecular weight of degrafted chains (GPC), a high brush grafting density was quantified as σ_“chains” = 0.354 chains·nm−2 (p(CHO)) and 0.280 (p(nPVE)) on 30 nm particles. These results prove a mechanistically validated, visible-light grafting-from strategy for generating vinyl ether and epoxy brushes on silica nanoparticles, thereby expanding the scope of Ge-mediated surface-initiated photopolymerization beyond radical systems.