Swelling-Induced Chain Stretching Enhances Hydrolytic Degrafting of Hydrophobic Polymer Brushes in Organic Media

Hydrophilic polymer brushes grown via surface-initiated polymerization from silicon oxide surfaces can detach or degraft in aqueous media. Degrafting of these chain endtethered polymers is believed to involve hydrolysis of bonds at the polymer-substrate interface. Degrafting so far has not been reported for hydrophobic polymer brushes in non-aqueous media. This study has investigated the degrafting and swelling properties of poly(tert-butyl methacrylate) (PtBMA) brushes in different water-miscible, organic solvents, viz. DMF, acetone and THF. In the presence of a sufficient quantity of water in the organic solvent, degrafting was also observed for PtBMA brushes. More importantly, however, the rate of degrafting depended on the nature of the organic solvent and the apparent initial rate constant of the degrafting reaction was found to correlate with the swelling ratio of the polymer brush in the different solvents. This correlation is first, direct evidence in support of the hypothesis that degrafting is facilitated by a tension that acts on the bond(s) that tether the polymer chains to the surface and which is amplified upon swelling of the polymer brush.