Reversible Reactions, Mesh Size, and Segmental Dynamics Control Penetrant Diffusion in Ethylene Vitrimers

Area of Science:

• Polymer Chemistry
• Materials Science
• Physical Chemistry

Background:

• Ethylene vitrimers are dynamic polymer networks with tunable properties.
• Understanding penetrant diffusion in these networks is crucial for material design.
• Borate ester cross-links enable dynamic bond exchange, influencing network behavior.

Purpose of the Study:

• To investigate the influence of network dynamics and penetrant-network interactions on diffusion.
• To quantify the effect of slow chemical reactions on molecular transport in vitrimers.
• To compare diffusion behavior in networks with varying cross-link exchange rates.

Main Methods:

• Fluorescence Recovery After Photobleaching (FRAP) was used to measure dye diffusion.
• Two aromatic dyes of similar size, one reactive and one inert, were employed.
• Kinetic modeling was applied to determine reaction rate constants.

Main Results:

• A reactive dye showed a 50-fold decrease in diffusion due to slow network reactions.
• A network with faster cross-linker exchange (10,000x) exhibited identical diffusion for both dyes.
• Diffusion was found to be dependent on mesh size, bond kinetics, and penetrant-network interactions.

Conclusions:

• Slow reaction kinetics can significantly impede penetrant transport in dynamic networks.
• Rapid cross-linker exchange minimizes the impact of chemical interactions on diffusion.
• Dynamic polymer networks offer tunable control over penetrant transport via synergistic effects.