Mixing effects on the mid-kilohertz mobility of polystyrene in glassy polystyrene-diluent blends

Abstract

Low molecular weight additive effects on the mid-kilohertz mobility of atactic polystyrene (PS) at 25°C via n.m.r. spin-lattice relaxation experiments in the rotating frame ( T 1 ϱ ) are analogous to the results of a previous study of diluents in glassy bisphenol-A polycarbonate. The diluent with a relatively low glass transition temperature ( T g), dioctylphthalate, increases the spectral density of thermal motions of the chain backbone and the pendant group in PS on the order of 38.5 kHz. Of the 13C nuclei in the glassy polymer, the relaxation behaviour of which can be differentiated by high-resolution, solid-state n.m.r., the T 1 ϱ 's of the aromatic carbons in the side group are affected most by dioctylphthalate. In contrast, the styrene oligomer, which has a higher T g than that of dioctylphthalate, does not significantly alter the ambient temperature mobility of polystyrene at 38.5 kHz. The PS-styrene oligomer and PS-dioctylphthalate blends are examples of athermal and non-athermal mixtures, respectively. However, the effect of the enthalpy of mixing on the T 1 ϱ 's of the polymer is probably obscured by differences in blend mobility due to different blend T g's.