In this work, a postpolymerization surface modification approach is reported that provides pendent thiol functionality along the polymer brush backbone using the photolabile protection chemistry of both o-nitrobenzyl and p-methoxyphenacyl thioethers. Poly(2-hydroxyethyl methacrylate) (pHEMA) brushes were synthesized via surface-initiated atom transfer radical polymerization, after which the pHEMA hydroxyl groups were esterified with 3-(2-nitrobenzylthio)propanoic acid or 3-(2-(4-methoxyphenyl)-2-oxoethylthio)propanoic acid to provide the photolabile protected pendent thiols. Addressing the protecting groups with light not only affords spatial control of reactive thiol functionality but enables a plethora of thiol-mediated transformations with isocyanates and maleimides providing a modular route to create functional polymer surfaces. This concept was extended to block copolymer brush architectures enabling the modification of the chemical functionality of both the inner and outer blocks of the block copolymer surface. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013