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 (Mw/Mn < 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.