Nuclear magnetic resonance approach to the characterization of the phase diagram of polyacrylonitrile in ternary solutions

Abstract

This work deals with the properties of the temperature-concentration phase diagram of ternary poly-acrylonitrile 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.