The propensity for covalent organic frameworks to template polymer entanglement
S Ephraim Neumann1,2, Junpyo Kwon3,4, Cornelius Gropp1,2
1Department of Chemistry, University of California-Berkeley, Berkeley, CA 94720, USA.
Science (New York, N.Y.)
|March 21, 2024
Summary
Molecularly woven covalent organic framework (COF) crystals create polymer-COF junctions in polyimide, enhancing composite strength and toughness. This programmable interaction allows for energy dissipation and improved material properties with minimal COF addition.
Area of Science:
- Materials Science
- Polymer Chemistry
- Nanotechnology
Background:
- Covalent organic frameworks (COFs) are crystalline porous materials with tunable structures.
- Integrating COFs into polymer matrices can enhance composite properties.
- Different polymer types interact distinctedly with COF fillers, influencing composite performance.
Purpose of the Study:
- To investigate the formation and impact of polymer-COF junctions in composite materials.
- To explore how molecularly woven COF crystals affect polymer chain arrangement and mechanical properties.
- To understand the role of polymer-filler interactions in enhancing composite performance.
Main Methods:
- Incorporation of 3D woven COF crystals into different polymer matrices (polymethyl methacrylate and polyimide).
- Characterization of filler-polymer interactions, including surface interactions and polymer chain threading.
- Mechanical testing of composite materials to evaluate strength, ductility, and toughness.
Main Results:
- Woven COFs form surface interactions with amorphous polymers but create polymer-COF junctions with liquid-crystalline polyimide.
- Polymer chain threading through COF pores enables programmable unthreading under stress, forming energy-dissipating nanofibrils.
- Small additions (~1 wt%) of COFs significantly enhance composite strength, ductility, and toughness by strengthening interfaces and lowering percolation thresholds.
Conclusions:
- The formation of polymer-COF junctions is crucial for achieving enhanced mechanical properties in COF-polymer composites.
- Polymer chain interaction with the COF framework is the key parameter for junction formation and subsequent property enhancements.
- Woven COF nanocrystals offer a promising strategy for developing high-performance polymer composites.
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