A thermosetting composition that includes an ungelled copolymer composition and a crosslinking agent. The ungelled copolymer composition includes a functional group-containing copolymer that includes segments of alternating residues derived from a donor monomer composition comprising an acceptor monomer composition. The donor monomer composition includes one or both of isobutylene and diisobutylene, and the acceptor monomer composition includes acrylic monomers and monomers containing functional groups. The ungelled copolymer composition is substantially free of transition metals and Lewis acids, and the copolymer is substantially free of maleate-type monomer residues and fumarate-type monomer residues. The crosslinking agent has at least two functional groups that are reactive with the functional groups of the copolymer. The thermosetting composition may be in liquid, powder, or dispersed form and may be applied by traditional or electrocoating methods.