The effect of the addition of carbonyl compounds such as amide, imide, urea, and ester derivatives on the dissolution rate of carboxyl-group-containing polymers in an alkaline solution was investigated. Urea derivatives lowered the dissolution rate of the polymer film more than the ether carbonyl compounds did, and 1,3-diphenylurea inhibited the dissolution of the polymer film much more efficiently than other urea derivatives. Structural studies of the dissolution inhibition led to the proposal of a supramolecular structure, in which the urea functionality hydrogen bonded to two carboxyl groups of the polymer to form a hydrophilic domain surrounded by the hydrophobic substituents of the urea derivatives. The existence of this supramolecular structure is supported by the infrared spectra of the urea additives in the polymer films.