Determination of domain sizes in heterogeneous polymers by solid‐state NMR

Abstract

Abstract Advanced solid‐state NMR techniques exploiting 1 H spin diffusion are described, which rely on selecting 1 H magnetization of one of the components on the basis of 1 H chemical shift or mobility differences under multiple‐pulse irradiation. To monitor the progression of 1 H spin diffusion, the higher resolution of 13 C 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 1 H 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 nm 2 /ms is expected to be typical for rigid organic systems. The domain sizes investigated range from approximately 1 nm to ca. 100 nm.