Determination of domain sizes in compatibilized polystyrene (ethylene-propylene rubber) blends by measurements of 1H spin diffusion

The size of domains in a series of compatibilized polystyrene-(ethylene-propylene rubber) blends were measured by solid-state NMR spin diffusion measurements. The average diameter of ethylene propylene rubber (EPR) particles in the blends was observed to decrease as the concentration of interfacial agent was increased up to ca. 15% (weight/volume of EPR) and remained constant upon further addition of interfacial agent. Comparison of the domain sizes obtained from NMR measurements with those obtained from scanning electron microscopy measurements suggests that the NMR technique can be used to confirm large-scale phase separation and investigate the trends in domain sizes in immiscible blends. It was found, however, that in these blends the spin diffusion is slow due to the large size of the domains; as a consequence the uncertainty of the size obtained from H-1 spin diffusion is fairly large. It was also found that mechanical grinding of the NMR samples can produce changes in the phase structure of the blends.