Synthesis of adaptive polymer brushes via "grafting to" approach from melt

We report a simple method to synthesize binary polymer brushes from two incompatible polymers of different polarity. The synthetic route is based on a subsequent step-by-step grafting of carboxyl-terminated polystyrene and poly(2-vinylpyridine) to the surface of a Si wafer functionalized with 3-glycidoxypropyl-trimethoxysilane. The end-functional polymers were spin-coated on the substrate, and grafting was carried out at a temperature higher than the glass transition temperature of the polymers. The composition of the binary brushes can be regulated based on grafting kinetics of the first polymer by the change of time or/and temperature of grafting. This method reveals a smooth and homogeneous polymer film on the macroscopic scale, while at the nanoscopic scale the system undergoes phase segregation effecting switching/adaptive properties of the film. Upon exposure to different solvents, the film morphology reversibly switches from "ripple" to "dimple" structures as well as the surface energetic state switches from hydrophobic to hydrophilic. The same switching of hydrophilic/hydrophobic properties was obtained for the different ratios between two grafted polymers in the binary brush.