Abstract
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.
Highlights
Titanium dioxide (TiO2) is a widely known pigment used in paints and sunscreens
Dopamine-based atom transfer radical polymerization (ATRP) initiators were used for functionalization of TiO2 NPs with polymer brushes by both grafting from [22] and grafting to [29] approaches
PDA-coated TiO2 NPs were reacted with α-bromoisobutyryl bromide (BiBB) to immobilize the ATRP initiator, following recently published procedures [32,33,34]
Summary
Titanium dioxide (TiO2) is a widely known pigment used in paints and sunscreens. TiO2 exhibits three distinct polymorhps, namely anatase, rutile and brookite; since the discovery of the semiconductive nature of anatase, TiO2 nanoparticles (NPs) have attracted tremendous interest in photovoltaics and photocatalysis [1,2,3]. SARA ATRP has been recently utilized to graft polymer brushes from various metal oxide NPs [27] or planar surfaces [28]. Dopamine-based ATRP initiators were used for functionalization of TiO2 NPs with polymer brushes by both grafting from [22] and grafting to [29] approaches. We report a facile route to polymer-grafted TiO2 NPs by combination of PDA chemistry and SARA ATRP. Grafting poly(butyl acrylate) (PBA) or PMMA from PDA-modified TiO2 particles of two different sizes (< 25 nm and 300 nm) is shown to proceed in a wellcontrolled manner, producing polymer brushes with low dispersities (Mw/Mn = 1.13–1.23), and high grafting densities (0.16–0.25 nm−2).
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