Aspects of the invention include methods for modifying a surface of a non-porous hydrophobic polymer substrate having a backbone containing electrophilic linkages. In practicing methods according to certain embodiments, a liquid composition having a nucleophilic reagent and a catalyst is contacted with the surface of the non-porous hydrophobic polymer substrate and maintained in contact with the surface of the polymer substrate in a manner sufficient to convert at least a portion of the surface from hydrophobic to hydrophilic while retaining the mechanical and optical properties of the polymer substrate. Substrates, including containers, having one or more hydrophilic surfaces and kits suitable for practicing the subject methods are also described.