The interaction of a sample of poly(methacrylic acid) with copper ions is investigated using various techniques: light and X-ray scattering, viscosimetry and fluorescence. The measurements were performed in the solubility domains and the regions where phase separation occurs were determined as a function of pH and copper/polymer ratio. We conclude that copper is mainly bound on the polymer through the formation of binuclear complexes implying pairs of adjacent carboxylates far along the chain. This induces a strong collapse of the chain at low ionisation degree and partially hinders the chain expansion at high pH. Fluorescence measurements can be interpreted through the existence of two different transitions: local and global transitions.