Separation of high-molecular-weight polymers differing just by one monomeric unit remains a challenging task. Here, we describe a protocol using metal-organic frameworks (MOFs) for the efficient separation and purification of mixtures of polymers that differ only by their terminal groups. In this process, polymer chains are inserted by threading one of their extremities through a series of MOF nanowindows. Selected termini can be adjusted by tuning the MOF structure, and the insertion methodology. Accordingly, MOFs with permanently opened pores allow for the complete separation of poly(ethylene glycol) (PEG) based on steric hindrance of the terminal groups. Excellent separation is achieved, even for high molecular weights (20 kDa). Furthermore, the dynamic character of a flexible MOF is used to separate PEG mixtures with very similar terminal moieties, such as OH, OMe, and OEt, as the slight difference of polarity in these groups significantly changes the pore opening kinetics.

In situ observation is a powerful and interesting technique for the characterization of functional materials in their working states. In this study, we used in situ dispersive X-ray absorption fine structure (DXAFS) measurements to observe the lattice oxygen dynamics in SrFeO3−δ and Sr3Fe2O7−δ during NO oxidation. The white-line intensities of Sr K-edge XAFS reflect the concentration of oxygen vacancies, and the lattice oxygen dynamics during NO oxidation are observed. Using a kinetics model, the rate-determining step (RDS) for NO oxidation was found to be an oxygen migration step. The activation energy obtained from the Arrhenius plots for Sr3Fe2O7−δ is much smaller than that obtained for SrFeO3−δ. Sr3Fe2O7−δ with a Ruddlesden–Popper-type layered perovskite can release oxygen with relatively small structural rearrangements. In contrast, SrFeO3−δ requires a significant rearrangement of oxygen vacancies to form the brownmillerite phase and the transformation restricts the oxygen release rate. The oxygen storage profiles with O2 also show that the RDS is the oxygen migration step, although the dissociative adsorption of O2 suppresses oxygen storage at low temperatures. The lattice oxygen dynamics obtained from the DXAFS measurements, which cannot be obtained from steady-state kinetics experiments, reveal the importance of the perovskite structure for NO oxidation.