Comparing Surface and Bulk Curing Processes of an Epoxy Vitrimer

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Vitrimers are advanced polymers with dynamic covalent networks, offering reprocessability.
• Understanding surface versus bulk curing is crucial for optimizing vitrimer performance.
• Bisphenol A diglycidyl ether (DGEBA) is a common epoxy resin used in vitrimer formulations.

Purpose of the Study:

• To investigate and compare the curing processes at the surface and in the bulk of a dicarboxylic acid-cured DGEBA vitrimer.
• To identify the key chemical species responsible for cross-linking in the vitrimer system.
• To analyze the impact of reprocessing on vitrimer properties.

Main Methods:

• Atomic force microscopy-based infrared spectroscopy (AFM-IR) for chemical imaging.
• Nanomechanical mapping (AFM-NM) for surface mechanical characterization.
• Quantitative analysis of IR peaks to assess esterification and curing extent.

Main Results:

• Identified β-hydroxy esters as key cross-linking agents in the DGEBA system.
• Surface curing is gradual and less extensive than bulk curing due to lower concentrations of functionalized β-hydroxy esters.
• Reprocessing leads to the formation of non-exchangeable esters, diminishing flowability and mechanical integrity.

Conclusions:

• Surface curing dynamics differ significantly from bulk curing in DGEBA vitrimers.
• The nanostructure heterogeneity is smaller at the surface compared to the bulk.
• Vitrimer reprocessability and mechanical properties are negatively affected by repeated processing cycles due to esterification changes.