Solid-state NMR characterization on the molecular-level homogeneity in lower critical solution temparature mixtures of poly(α-methyl styrene) and poly(2,6-dimethyl-p-phenylene oxide)

The length scale of heterogeneity in blends of poly(2,6-dimethyl-p-phenylene oxide) (PPO) with poly(α-methyl styrene) (PαMS) was investigated using solid state ¹³C NMR. The PPO/PαMS blend system was homogeneous at ambient, but phase separation at or above the lower critical solution temperature (LCST) was confirmed by polarized-light microscopy (PLM) and differential scanning calorimetry (DSC). Fourier-transform infrared spectroscopy (FT-IR) characterization confirmed that there was no specific interaction between PPO and PαMS. The scales of homogeneity in the blend were examined. ¹H spin-relaxation times in the laboratory frame (T₁^H) and in the rotating frame (T_1p^H) were measured for PPO/PαMS blends of various compositions and neat polymer components (PPO, PαMS). T_1p^H data indicated that PPO and PαMS are mixed at the molecular level for all compositions, showing that the miscibility scale is comparable with that of the classical blend system of PPO and polystyrene (PS).