High-Resolution Solid-State 13C NMR Study on Effects of Blending on Chain Dynamics in Polystyrene/Poly (Vinyl Methyl Ether) Blends
To clarify effects of blending on motions of the individual polymer components in the compatible blend polystyrene/poly (vinvl methyl ether) (PS/PVME), temperature dependence of the 13C NMR linewidth for the CH carbon in PVME was studied under magic-angle spinning and proton dipolar-decoupling. The observed temperature dependence above the glass transition temperature was satisfactorily explained by assuming that the tempereature dependence is brought about by the effects of molecular motions as follows: (1) the averaging of the dispersion of the isotropic chemical shifts in the glass state, and (2) the interference of the local anisotropic motion and high-power proton decoupling.
The activation parameters for the motion of PVME in each blend could be described by a single Arrhenius equation. No distribution for the pre-exponential factor nor for the activation energy were discernible. Three main effects of blending on motion are appreciable: with increasing the PS content, (I) the characteristic temperature for the onset of the motion of PVME increases, (II) the activation energy E& decreases, and (III) the anisotropy of the motion increases. These lead us to conclude that microscopically homogeneous mixing is achieved for PS/PVME. This conclusion is in accordance with the DSC results, 1 and the observation of the 9fast spin diffusion in polarization-transfer experiments, 2 and the two-dimensional exchange H NMR in solids. 3