Grafting mixed responsive brushes of poly(N-isopropylacrylamide) and poly(methacrylic acid) from gold by selective initiation

Mixed polymer brushes consisting of poly(N-isopropylacrylamide) (PNIPAM) and poly(methacrylic acid) (PMAA) were prepared at room temperature by a sequential combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and iniferter-mediated photopolymerization (SI-IMP). Mixed monolayers of disulfides of ATRP initiator and IMP iniferter on gold substrates were employed for independent initiation of the two polymer components. As the polymerization of PNIPAM and PMAA was performed in successive steps, the chain length and the corresponding brush height of the constituents could be individually controlled. Grazing angle Fourier transform infrared spectroscopy (FTIR) and ellipsometry were performed to monitor the component-specific formation of the grafts. The responsive behavior of the mixed polymer brushes under different pH was investigated by contact angle (CA) measurements, atomic force microscopy (AFM) and in situ ellipsometry. Reversible structural reorganization and variation of brush thickness and of wetting characteristics were monitored.