A laboratory exercise for the synthesis of a sulfonated styrene-"co"-maleic anhydride polymer and its application as a stain blocker on nylon-6,10, is described. The effectiveness of the sulfonated polymer to prevent the conjugate base of an acid dye from staining the polyamide is demonstrated. This experiment is designed for second-semester, second-year undergraduate organic chemistry students. Specifically, this laboratory experiment focuses on providing experience with radical chain and step-growth polymerizations, interfacial reactions, electrophilic aromatic substitution (sulfonation), and the importance of intermolecular forces.