This work deals with the properties of the temperature concentration phase diagram of ternary polyacrylonitrile solutions that were mainly observed from the transverse magnetic relaxation of protons attached to polymer chains, used to disclose the presence of solid-state domains. The binary solvent was a mixture of dimethylformamide (DMF) and water; the molar fraction of monomeric units was varied from 0 to 0.5, while the relative molar fractions of DMF and water were 1:1 or 2:1. The solvent quality was found to decrease upon addition of water. A curve (liquidus) that relates the temperature of formation of solid-state domains to the initial polymer concentration in solution was drawn from nuclear magnetic resonance (n.m.r.). The demixing part of the liquidus, determined as a plateau from n.m.r., was identified on observing a cloud-point curve. The main feature of the phase diagram concerns the specific behaviour of solutions observed whenever the concentration of disordered segments becomes lower than half the initial polymer concentration.