Core-shell particles were prepared using a two-stage emulsion polymerization of styrene and ethyl acrylate. The particle surfaces were modified by introducing an acetal functionality, suitable for acid-catalyzed crosslinking processes. Surface functionalization was performed in two principally different ways : In the first method, 4-aminobutyraldehyde dimethylacetal was used for grafting through transesterification of ethyl acrylate residues at the surface or through reactions with epoxy groups introduced in the second-stage polymerization. In the second method, 4-acrylamidobutyraldehyde dimethylacetal was used as a comonomer to ethyl acrylate in the second-stage polymerization. The reactive particles were used as crosslinking agents in an acid-curing coating system.