Disulfide-Initiated Addition-Fragmentation Chain Transfer in Allyl Sulfide-Based Vitrimers.

Area of Science:

• Polymer Chemistry
• Materials Science
• Sustainable Chemistry

Background:

• Covalent adaptable networks (CANs) offer reprocessability and recyclability.
• Traditional thermosets possess desirable properties but lack recyclability.
• Dynamic covalent bonds are key to CANs' adaptable nature.

Purpose of the Study:

• To develop novel radical-based vitrimers.
• To utilize addition-fragmentation chain transfer reactions for dynamic covalent bonding.
• To create recyclable thermoset materials with retained properties.

Main Methods:

• Synthesized vitrimers via crosslinking epoxy monomers with allylic functionalities.
• Employed a disulfide-containing hardener for thermally activated radical generation.
• Varied disulfide hardener proportions and analyzed stress relaxation and reprocessing.

Main Results:

• Achieved stress relaxation in all prepared vitrimers.
• Demonstrated dynamic behavior with a 21-minute relaxation time at 200°C using only 10 mol% disulfide.
• Confirmed full material reversibility over three reprocessing cycles without property degradation.
• Determined activation energy for the exchange mechanism to be 48 (±4) kJ/mol.

Conclusions:

• Successfully developed thermally activated, radical-based vitrimers.
• Established a novel approach for designing recyclable thermoset materials.
• Highlighted the potential of these CANs for sustainable material applications.