Bidimensional Response Maps of Adaptive Thermo- and pH-Responsive Polymer Brushes

We depict the collapse transition of adaptive thermo- and pH-responsive copolymer brushes based on poly(di(ethylene glycol) methyl ether methacrylate-co-methacrylic acid) random copolymer chains (P(MEO2MA-co-MAA)) by drawing bidimensional (2D) maps of the swelling ratio versus temperature and pH for different brush compositions. The collapse transition is probed by quartz crystal microbalance measurements with dissipation monitoring (QCM-D). While P(MEO2MA) brushes exhibit a thermo-collapse transition around 22 °C and P(MAA) brushes display a pH-induced collapse transition at pH = 5.5, P(MEO2MA-co-MAA) brushes undergo a collapse transition modulated by either temperature or pH from a swollen state at low temperature and high pH to a collapsed state at high temperature and low pH. By varying the composition of the copolymer in MAA units from 4 to 14 mol %, the brushes switch from a pH-modulated thermo-responsive behavior to a temperature-modulated pH-responsive behavior in water. The 2D maps of swelling ratio also illustrate the complex interplay between pH and temperature, and provide a unique view of the response of adaptive brushes.