Selective sorting of polymers with different terminal groups using metal-organic frameworks

Abstract

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.

Enhancement of orientation of rigid polymer blocks by incorporating rod–coil block copolymer chains into metal–organic frameworks

“…It should be noticed that this simulation work has introduced an exemplary copolymer chain into a MOF, only to show the feasibility of our proposed strategy for enhancing the orientation of rigid polymer blocks. An experimental realization of this strategy should consider the choice of the copolymer chain and MOF with respect to a more detailed experiment process and the steric hindrance effect . Nevertheless, the findings of this work help to provide theories and predictive methods for the selection of polymers and MOFs that may be ideal for the enhancement of orientation of rigid polymer materials.…”

“…film‐type, polymers, and the polymers might gradually lose their structural order after the external mechanical force is removed. Recently, a new strategy utilizing metal–organic frameworks (MOFs) to align the polymers has been proposed . This strategy is very promising, because MOFs can provide a restricted nano‐space to realize the in situ polymerization of monomers and the alignment of the polymer chains simultaneously.…”

“…However, it is still challenging to precisely control the loading amounts of the monomers, the degree of polymerization and thus the molecular weight of the polymer chains. As an alternative way, the polymer chain could be incorporated directly into the MOF channels by immersing the MOF in the melting polymer or a solution with dissolved polymer . This way is quite effective with respect to the above considerations, especially for those polymers that are not easily polymerized inside the MOF channels.…”

“…Recently, a new strategy utilizing metal-organic frameworks (MOFs) to align the polymers has been proposed. [17][18][19][20][21][22][23][24][25][26] This strategy is very promising, because MOFs can provide a restricted nano-space to realize the in situ polymerization of monomers and the alignment of the polymer chains simultaneously. In the work of Distefano et al, 18 polystyrene (PSt) was prepared by in situ polymerization in a MOF, and the ordered PSt was extracted by washing the composites (MOF including PSt) with Na 2 -EDTA.…”

“…As an alternative way, the polymer chain could be incorporated directly into the MOF channels by immersing the MOF in the melting polymer or a solution with dissolved polymer. [22][23][24][25][26] This way is quite effective with respect to the above considerations, especially for those polymers that are not easily polymerized inside the MOF channels. For instance in the work of Kitao et al, 25 a polysilane (PMPrS) chain was successfully introduced into a MOF, and extracted from the MOF in Na 4 -EDTA solution.…”