Miscibility of an oligo(p-phenylenevinylene) with polystyrene studied by solid-state nuclear magnetic resonance

Molecular proximity of cis/trans mixtures of 2,5-dimethoxy-1,4-bis[2-(3,4,5-trimethoxyphenyl)vinyl]benzene (MPV, 1) and polystyrene (PS) in mixtures of different MPV/PS weight ratios up to 60/40 is shown by 1H combined rotation and multiple pulse spectroscopy (CRAMPS) using 2D exchange experiments. The MPV/PS mixtures up to a weight ratio 60/40 are homogeneous, whereas the mixture with a weight ratio MPV/PS = 80/20 is heterogeneous. The comparison of the cross polarization/magic angle spinning (CP/MAS) 13C NMR spectra of pure MPV and of MPV mixed with PS shows significant linebroadening in case of intimate mixing, while the heterogeneous mixture shows some extra finestructure. The miscibility results were confirmed by proton spin-locking relaxation time measurements (T1ρH) on the mixtures. On intimate mixing, T1ρH is averaged out and varies linearly as a function of the composition of the mixture. CRAMPS-spectra and T1ρH measurements show that iodine-doped MPV/PS mixtures (weight ratios 40/60 and 60/40) are heterogeneous. Furthermore, doping causes a slight proton chemical shift change and reduces the T1ρH-values of those oligomer-polymer systems.