The present invention provides a coating additive copolymer comprising, as copolymerized units, by dry weight based on total dry weight of the copolymer, from 20% to 60%, at least one acetoacetoxy or acetoacetamide functional ethylenically unsaturated monomer, and from 40% to 80% at least one water soluble ethylenically unsaturated monomer. It further provides a coating formulation comprising higher than 0.04% by dry weight based on total dry weight of the coating formulation, the acetoacetoxy or acetoacetamide functional ethylenically unsaturated monomer.