Efficient water-soluble drag reducing star polymers with improved mechanical stability

We describe here the first example of the synthesis of 4-arm star poly(acrylic acid) for use as a water-soluble drag reducing agent, by applying Cu(0)-mediated polymerization technique. High molecular weight 4-arm star poly(tert-butyl acrylate) (Mn = 3.0-9.0 x 10 5 g mol -1 ) was first synthesized using 4,4’-oxybis(3,3-bis(2-bromopropionate)butane as an initiator and a simple Cu(0)/TREN catalyst system. Then, 4-arm star poly(tert-butyl acrylate) were subjected to hydrolysis using trifluoroacetic acid resulting in water-soluble 4-arm star poly(acrylic acid). Drag reduction test rig analysis showed 4-arm star poly(acrylic acid) to be effective as a drag reducing agent with drag reduction of 24.3 %. Moreover, 4-arm star poly(acrylic acid) exhibited superior mechanical stability when compared with a linear poly(acrylic acid) and commercially available drag reducing polymers; Praestol and poly(ethylene oxide). The linear poly(acrylic acid), Praestol and poly(ethylene oxide) all showed a large decrease in drag reduction of 8-12 % when cycled 30 times through the drag reduction test rig whilst, in contrast, 4-arm star poly(acrylic acid) demonstrated much higher mechanical stability.