Swelling and\nDegrafting of Poly(3-sulfopropyl methacrylate)\nBrushes

Upon exposure to a good solvent, polymer brushes prepared\nvia surface-initiated\npolymerization can undergo degrafting via cleavage of bonds that anchor\nthe polymer tethers to the underlying substrate. As polymer brushes\nare often used in a solvent swollen state, this has implications for\nthe longevity of these polymer coatings. Improving the fundamental\nunderstanding of this process is thus also of practical importance.\nIt is believed that degrafting is the consequence of tension amplification\nat the bonds that anchor the polymer grafts, which is driven by swelling\nof the polymer brush film. Taking advantage of the sensitivity of\nthe swelling behavior of poly(3-sulfopropyl methacrylate) (PSPMA)\nbrushes toward changes in ionic strength, this study has investigated\nthe degrafting behavior of these brushes in aqueous media at different\nLiCl and NaCl concentrations. The aim of these experiments was to\ninvestigate whether the rate constant of the degrafting process was\ncorrelated with the swelling ratio of the PSPMA brushes. The experiments\nshow that in aqueous LiCl solutions, the initial rate constant of\nthe degrafting process is correlated with the swelling ratio of the\nPSPMA brush. This observation represents a first example of the correlation\nbetween these two parameters for hydrophilic polymer brushes in aqueous\nmedia and supports the idea that degrafting is a mechanochemical process\ndriven by a swelling-induced tension at the polymer–substrate\ninterface.