By electrochemical and spectroscopic methods the interaction of acrylic acid and vinylbutyl ether, acrylic acid and styrene, vinyl ether of monoethanol amine and styrene copolymers with some anionic (polyacrylic and polymethacrylic acids) and cationic (polyvinyl ether of monoethanol amine and poly-N-methyl-4-vinylethynyl piperidole-4) polymers have been investigated in a solution and on the boundary of two non-mixing liquids. The formation of interpolymer complexes with exact composition occurs. Upon realization of complexation on the liquid-liquid boundary the complex formation reaction has some time, caused obviously by diffusion of interacting macromolecules to the interface layer where the interaction takes place.