Abstract Polyacids form polymer complexes with polybases (proton acceptors) through hydrogen bonds. This result is well-known for homopolymer/homopolymer mixtures but only a few studies have been devoted to homopolymer/copolymer pairs because of the complexity of such systems. In this study a very simple model is proposed to take into account the influence of uncomplexable groups in the copolymer chain on complex formation. Several polybases (polyoxyethylene, polyvinylmethylether, polyvinylpyrrolidone) are used as homopolymers, and partially neutralized poly(acrylic acid) as copolymer; the acrylate groups are uncomplexable and behave as structure defects. It was found that the degree of complexation increases continuously with the concentration ratio [polybase]/[polyacid]. There is an exponential relation between the degree of complexation and the number of structural defects on the copolymer chain.