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Unimolecularly thick monosheets of vinyl polymers fabricated in metal-organic frameworks

 The University of Tokyo announced on 17 July 2020, that the researchers have developed unimolecularly thick polymer sheets by using nanospaces of metal-organic frameworks as templates. The work was directed by Professor Takashi Uemura at Graduate School of Frontier Science of the University with the support by KAKENHI from MEXT and results were published in Nature Communications *).

 Polymer sheets are widely used in various industrial products and there exist strong requirements for thinner sheets. However, because of the limitations of conventional coating and drawing methods, no technology has been developed to produce polymeric sheets thinned down to the molecular level in a reasonable manner and in large quantity until now.

 In this work, researchers made unimolecularly thick polymer sheet by exploiting the controlled 2D nanospaces of pillar-layer metal-organic frameworks (MOFs). Styrene monomer (thickness:~0.7nm) was inserted into the nanospace (height:~0.8nm) of MOF then the crosslinking radical polymerization was performed. After the removal of the MOFs with acid, unimolecularly thick polystyrene sheet was obtained. The size of the sheet was ~100nm and the molecular weight was ~300,000g・mol-1. Thickness of nanosheets is controlled by selecting the space of MOF as shown experimentally to make 1.2nm-thick sheets.

 Owing to the 2D crosslinked structure and suppressed chain entanglements, the polystyrene sheet exhibits unique properties such as lower glass transition temperature, higher flexibility and higher solubility compared to the conventional linear or 3D crosslinked polystyrene. The method has potential for large scale production and can be universally applied to many radical polymers with various structures of MOFs. The researchers aim to use the unimolecularly thick monosheets as the modifier for polymeric materials.

*) Nobuhiko Hosono, Shuto Mochizuki, Yuki Hayashi, and Takashi Uemura, "Unimolecularly thick monosheets of vinyl polymers fabricated in metal-organic frameworks", Nature Communications, Vol. 11, Article number: 3573 (2020), doi: 10.1038/s41467-020-17392-1; Published: 17 July 2020