Surface-initiated ATRP from polydopamine-modified TiO₂ nanoparticles

A robust approach for modification of TiO₂ nanoparticles with polymer brushes by atom transfer radical polymerization (ATRP) is presented. TiO₂ surface was first coated with polydopamine (PDA) followed by immobilization of an ATRP initiator, α-bromoisobutyryl bromide (BiBB). Poly(methyl methacrylate) (PMMA) and poly(butyl acrylate) (PBA) were then grafted from the PDA-modified TiO₂ of different size (25 and 300 nm) in DMF at room temperature via supplemental activator reducing agent (SARA) ATRP using only 100 ppm of the copper catalyst. Hybrid core-shell particles with high organic contents (40–88 wt%) and grafting densities (0.16–0.25 nm⁻²) were obtained. Reaction conducted in the presence of sacrificial initiator confirmed excellent control over the polymerization and produced PMMA and PBA with narrow molecular weight distributions (M_w/M_n < 1.25). Obtained particles were tested as lubricating additives in pipe dope compositions. Addition of polymer-grafted TiO₂ to the base grease resulted in a reduced coefficient of friction (COF) and wear over uncoated TiO₂ as revealed by reciprocating pin-on-disc tests. The model pipe dopes with PMMA-grafted particles were found to perform on par with commercial American Petroleum Institute (API) dope.