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

Covalent adaptable networks (CANs) have emerged as a promising class of materials that incorporate dynamic covalent bonds, enabling reprocessability and recyclability while retaining the advantageous properties of traditional thermosets. Herein, we report a class of radical-based vitrimers employing addition-fragmentation chain transfer reactions. The vitrimer was synthesized via crosslinking of an epoxy monomer containing embedded allylic functionalities capable of undergoing exchange through a degenerative transfer mechanism. The generation of thiyl radicals necessary for the exchange is triggered by a disulfide-containing hardener which reversibly generates radicals upon thermal activation. Vitrimers were prepared with varying proportions of the disulfide hardener relative to a permanent hardener. All materials exhibited stress relaxation, with relaxation times dependent on the disulfide content. Incorporation of only 10 mol% of disulfide resulted in a relaxation time of 21 min at 200 °C, demonstrating dynamic behavior. Full reversibility was confirmed after three reprocessing cycles, with no significant change in glass transition temperature (Tg), storage modulus, and FTIR spectra. Additionally, a model reaction was conducted to prove the exchange mechanism, revealing an activation energy in the range of 48 (± 4) kJ.mol^-1. This study introduces a novel approach to thermally activated, radical-based vitrimers, expanding the design for recyclable thermoset materials.