Molecular Motion in Miscible Polymer Blends. 1. Motion in Blends of PEO and PVPh Studied by Solid-State 13C T1ρ Measurements

Changes in molecular motion in blends of PEO−PVPh have been studied using measurements of 13 C T 1 ρ relaxation times. 13 C T 1 ρ relaxation has been confirmed as arising from spin−lattice interactions by observation of the variation in T 1 ρ with rf field strength and temperature. In the pure homopolymers a minimum in T 1 ρ is observed at ca. 50 K above the glass transition temperatures detected by DSC. After blending, the temperature of the minimum in T 1 ρ for PEO increased, while that for PVPh decreased, however, the minima, which correspond to the temperatures where the average correlation times for reorientation are close to 3.1 μs, are separated by 45 K (in a 45% PEO−PVPh blend). These phenomena are explained in terms of the local nature of T 1 ρ measurements. The motions of the individual homopolymer chains are only partially coupled in the blend. A short T 1 ρ has been observed for protonated aromatic carbons, and assigned to phenyl rings undergoing large-angle oscillatory motion. The effects of blending, and temperature, on the proportion of rings undergoing oscillatory motion are analyzed.