13 C NMR spin–lattice relaxation times as a probeof local polymer dynamics in plasticized polyethers

¹³C NMR spin–lattice relaxation times <i>T</i>₁ are used to investigate the effect of low molecular weight diluents, including <i>N,N</i>-dimethylformamide, <i>N</i>-methylformamide, propylene carbonate, <i>γ</i>-butyrolactone, triglyme and tetraglyme, on the local polymer segmental motion in polyether–urethane networks. In all cases, an increase in the local mobility is deduced from the increasing <i>T</i>₁ measurements consistent with a decreasing glass transition temperature. The extent of plasticization, however, is dependent on the nature of the small molecules. Those molecules which can either form strong polymer-diluent interactions (for example through dipolar interactions) or are themselves rigid, give the least enhancement of polymer mobility and the greatest deviation from the Fox equation for <i>T</i>_g. In the presence of alkali metal salts, <i>N,N</i>-dimethylformamide and propylene carbonate are shown to have opposite effects on the local polymer motion, as seen from the <i>T</i>₁ measurements. In both cases, addition of the plasticizers increases the ¹³C <i>T</i>₁ relaxation times for the plasticizer. However, propylene carbonate decreases the polymer ¹³C <i>T</i>₁ whilst <i>N,N-</i>dimethylformamide results in the expected increase in polymer ¹³C <i>T</i>₁.<br />