PFBT was purchased from Ossila. PFBT from the same batch was treated by Brilliant Matters to remove palladium until it was below the detection limit of 10 ppm. Polystyrene grafted with carboxy-terminated polyethylene oxide (PS-PEG-COOH, backbone chain Mw 8500 g mol -1 , graft chain Mw 4.6 kDa, total chain 36500 g mol -1 ) was purchased from Polymer Source Inc. All solvents and other chemicals are purchased from Sigma-Aldrich and used as received unless stated otherwise.