13C c.p./m.a.s. n.m.r. study on the miscibility and phase separation of a polystyrene/poly(vinyl methyl ether) blend

Abstract

We investigate the miscibility of a polystyrene/poly(vinyl methyl ether) (PS/PVME) blend using nuclear magnetic resonance spectroscopy. We examine 1 H spin-lattice relaxation times in both the laboratory ( T 1H ) and rotating ( T 1ρH ) frames at various temperatures. At temperatures lower than the glass transition temperature ( T g ) of the blend, the observed 1 H relaxation time of PS is equal to that of PVME, showing that the 5/5 PS/PVME blend is miscible on a scale of 20–30 A. At temperatures much higher than T g , the observed 1 H relaxation curve ( T 1 ρ H ) of PS apparently differs from that of PVME. They are not single exponentials. The non-exponential decays are analysed taking into account spin diffusion; the 1 H spin diffusion rate between PS and PVME is found to be ∼ 1000s −1 at 38°C. This spin diffusion rate is too slow for the T 1ρH values of PS and PVME to coincide with each other. This is attributed to the fast molecular motion of PVME. The 1 H relaxation curve of the phase-separated blend formed by heating above the lower critical solution temperature is markedly different from that of the homogeneous blend. On the assumption that 1 H spin diffusion does not occur between phase-separated domains, we analyse the 1 H relaxation curve of each component polymer and obtain the stoichiometry of the phase-separated domains. We conclude that the phase separation of the 5/5 PS/PVME blend is initiated by spinodal decomposition; the phase separation rate is 0.5 min −1 at 140°C.