Spontaneous degrafting of weak and strong polycationic brushes in aqueous buffer solutions

Polymers grafted to substrates have usually been considered to be stable because of the covalent bonds that anchor the macromolecules to the substrate. Several recent reports have reported on degrafting polymers from substrates under specific conditions. We have conducted a systematic study of degrafting polycationic brushes with different degrees of quaternization (DQ), molecular weight, grafting density, which have been incubated in buffer solutions (pH 4, 7.4, and 9) with the same ionic strength (0.05 M). We also explored the effect of the bonding environment at the anchoring point of the polymer graft on the overall stability of polymer assemblies on the substrate. The major findings in this study are: 1) Degrafting of polycationic grafts from flat silica substrate increases with increasing DQ of the polymer, 2) Polymer degrafting likely occurs both in the initiator ester group and the silane head-group at the silicon substrate, 3) The degrafting kinetics can be described by time-dependent rate constant modeled by stretched exponential function.