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

Abstract

¹³ C NMR spin–lattice relaxation times T ₁ are used to investigate the effect of low molecular weight diluents, including N,N-dimethylformamide, N-methylformamide, propylene carbonate, γ-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 T 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 T _g . In the presence of alkali metal salts, N,N-dimethylformamide and propylene carbonate are shown to have opposite effects on the local polymer motion, as seen from the T ₁ measurements. In both cases, addition of the plasticizers increases the ¹³ C T ₁ relaxation times for the plasticizer. However, propylene carbonate decreases the polymer ¹³ C T ₁ whilst N,N-dimethylformamide results in the expected increase in polymer ¹³ C T ₁ .