Interpolymer complexation is associated with the formation of hydrogen bonds between pendent and/or grafted groups of a single polymer or copolymers. The degree of complexation can be described theoretically in terms of complexation/decomplexation equilibrium characteristics. Graft copolymer networks of poly(methacrylic acid-g-ethylene glycol) were prepared by free radical solution polymerization of methacrylic acid and poly(ethylene glycol) monomethacrylate. The ensuing gels exhibited drastic network structural changes in response to environmental pH changes due to the formation/dissociation of interpolymer complexes. The molecular level degree of complexation was determined as a function of copolymer composition, PEG graft chain molecular weight and environmental pH. The largest degrees of complexation were observed in gels containing nearly equimolar amounts of the monomeric units and the longest molecular weight poly(ethylene glycol) grafts. These trends were predicted by the equilibrium complexation theory and were in good agreement with the experimental data.