Analysis of gas transport properties of PPO/PS blends by 129Xe NMR spectroscopy

Relationships among variations of microvoids and gas transport properties for miscible poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)/polystyrene (PS) blends in the glassy state have been investigated by Xe sorption, Xe permeation, and 129Xe NMR measurements. Xe sorption isotherms of the blends can be interpreted successfully on the basis of the dual-mode sorption model. Decrease in the permeability of Xe is attributed to the decrease in the diffusivity of that in the Langmuir site. 129Xe NMR spectra of 129Xe in the blends show non-linear low-field shift with increasing sorption amount of Xe because of a fast exchange of Xe atoms between Henry and Langmuir sites. From the analysis of 129Xe NMR chemical shifts, it is found that the mean volume of individual microvoids varies with a negative deviation against volume fraction of PPO in the blend. For PPO/PS blends, it has been clarified that the contraction of individual microvoids occurs by blending and highly affects gas transport properties.