Structure and mobility in poly(ethylene oxide) poly(methyl methacrylate) blends investigated by C-13 solid-state NMR

Solid-state C-13 CP/MAS/DD NMR measurements have been carried out at 300 K on melt-mixed blends of poly(ethylene oxide)/atactic poly(methyl methacrylate) (PEO/alpha-PMMA) in the concentration range 10/90 to 75/25. Several relaxation times for protons and carbons, i.e. relaxation in the rotating frame (T-1 rho(H-1) and T-1 rho(C-13)) and in the laboratory frame (T-1(H-1) and T-1(C-13)), have been studied. From the carbon relaxations, we conclude that mixing is intimate enough to cause a reduction in local chain mobility for amorphous PEG. Although intermolecular spin diffusion contributes to the proton relaxations in accordance with homogeneity, T-1(H-1) and T-1?rho(H-1) data show signs of incomplete averaging. The proton relaxation behavior indicates the existence of heterogeneous domains with shortest dimensions in the nanometer range, which is further supported by the carbon relaxation decays and equilibrium C-13 MAS/DD spectra.