Solid-state NMR and small-angle X-ray scattering study of microphase structure of amorphous and semicrystalline poly(styrene-ethylene oxide) diblock copolymers

The microphase structure of a series of poly(styrene-ethylene oxide) (SEO) block copolymers has been studied by solid-state NMR and small-angle X-ray scattering (SAXS) techniques. The differential scanning calorimetry studies indicate that the majority of SEO samples are semicrystalline. For the com pletely amorphous SEO, solid-state NMR TK spin diffusion was used to determ ine the sizes of various domains, interfacial thickness, and interdomain di stances by the initial-rate approximation and by numerical simulation with a pure spin diffusion model. The results obtained from the above two method s, the initial-rate approximation and the numerical simulation, are general ly in good agreement, but the interdomain distance estimated from NMR is re latively lower than that obtained From SAXS. The discrepancy is probably ca used by the simulation model used in the NMR data interpretation. For the s emicrystalline SEO samples, the relative locations of multiple Bragg peaks and the location of the first-order maximum in the SA;YS data were used to determine the morphology and the size of the interdomain distance of the ma terial. This is a typical example where either NMR or SAXS alone cannot yie ld complete phase structure information for both amorphous and semicrystall ine SEO materials. A combination of the above two techniques is necessary a nd allows us to explore the phase structure of both the amorphous and the s emicrystalline SEO samples and also examine the validity of the pure spin d iffusion model used for the NMR analysis.