DETERMINATION OF DOMAIN SIZES IN HETEROGENEOUS POLYMERS BY SOLID-STATE NMR

Advanced solid-state NMR techniques exploiting H-1 spin diffusion are described, which rely on selecting H-1 magnetization of one of the components on the basis of H-1 chemical shift or mobility differences under multiple-pulse irradiation. To monitor the progression of H-1 spin diffusion, the higher resolution of C-13 CP MAS spectra is exploited for NMR detection. For evaluation of the data, full quasi-analytical solutions of the diffusion equation as well as initial-rate approximations are derived, applied, and discussed. In order to obtain quantitative results, the H-1 spin-diffusion constant has to be determined. To this end, the domain sizes in poly(styrene)-poly(methyl methacrylate) systems including symmetrical diblock copolymers have been measured. The comparison of the NMR results with SAXS and TEM data yields the spin-diffusion coefficient for PS and PMMA. The resulting value of D = 0.8 nm2/ms is expected to be typical for rigid organic systems.The domain sizes investigated range from approximately 1 nm to ca. 100 nm.