2024-03-21 カリフォルニア大学バークレー校(UCB)
Photo: Schematic illustration of the COF structure, polymers, and nanofibrils courtesy of Science Magazine
＜関連情報＞
- https://chemistry.berkeley.edu/news/molecular-weaving-makes-polymer-composites-stronger-without-compromising-function
- https://www.science.org/doi/10.1126/science.adf2573
高分子の絡み合いを鋳型とする共有結合性有機フレームワークの性質 The propensity for covalent organic frameworks to template polymer entanglement
S. EPHRAIM NEUMANN , JUNPYO KWON , CORNELIUS GROPP , LE MA , […], AND OMAR M. YAGHI
Science Published:21 Mar 2024
DOI:https://doi.org/10.1126/science.adf2573
Editor’s summary
Liquid crystalline polymers can thread through covalent organic frameworks (COFs) and create nanofibril bridges that dissipate energy during fracture. Neumann et al. show that a molecularly woven COF stabilized by amide linkages was interpenetrated by polyimide, which was also chemically similar to this COF. However, polymethyl methacrylate, which is a brittle and amorphous polymer, only coated the COF particles and formed surface entanglements. The polyimide composite had greater fracture toughness and formed polyimide nanofibrils at the fracture surfaces. —Phil Szuromi
Abstract
The introduction of molecularly woven three-dimensional (3D) covalent organic framework (COF) crystals into polymers of varying types invokes different forms of contact between filler and polymer. Whereas the combination of woven COFs with amorphous and brittle polymethyl methacrylate results in surface interactions, the use of the liquid-crystalline polymer polyimide induces the formation of polymer-COF junctions. These junctions are generated by the threading of polymer chains through the pores of the nanocrystals, thus allowing for spatial arrangement of polymer strands. This offers a programmable pathway for unthreading polymer strands under stress and leads to the in situ formation of high-aspect-ratio nanofibrils, which dissipate energy during the fracture. Polymer-COF junctions also strengthen the filler-matrix interfaces and lower the percolation thresholds of the composites, enhancing strength, ductility, and toughness of the composites by adding small amounts (~1 weight %) of woven COF nanocrystals. The ability of the polymer strands to closely interact with the woven framework is highlighted as the main parameter to forming these junctions, thus affecting polymer chain penetration and conformation.
