Synthesis of Binary Polymer Brushes via Two-Step Reverse Atom Transfer Radical Polymerization

Well-defined poly(n-butyl acrylate) (PnBA)/poly(acrylic acid) (PAA) binary brushes grafted from silicon surfaces have been successfully prepared via a two-step reverse atom transfer radical polymerization (reverse ATRP) of n-butyl acrylate and tert-butyl acrylate initiated from tethered diazo groups and subsequent hydrolysis of poly(tert-butyl acrylate) (PtBA). The final molar ratio of PnBA/PAA brushes was well-controlled by limiting the time allowed for the initial decomposition of a fraction of the diazo-initiator at higher temperature. After initiating growth of polymer chains from the surface-tethered initiator and deactivation by the Cu(II) complex, ATRP was carried out at 40 °C to achieve desired molecular weight while preventing further decomposition of the remaining unreacted diazo-initiator from which the PtBA brushes were grown in the second step. Measurement of film thickness, contact angle, and surface morphology of the resulting surfaces confirmed the PnBA/PAA binary brush structures and demonstrated how surface properties changed with composition. The morphologies of the surfaces were affected by treatment with a selective solvent, such as water or toluene, and a nonselective solvent, chloroform/methanol (1:1 by volume).