biostudies-literatureKwon Wthe Institute of Civil Military Technology Cooperation funded by the Defense Acquisition Program Administration and Ministry of Trade, Industry and Energy of Korean governmentDefense Acquisition Program Administration and Ministry of Trade, Industry, and Energy of the Korean government695https://www.ebi.ac.uk/biostudies/studies/S-EPMC11902468biostudies-literatureUnknown17(5)Fracture toughness is a key property of epoxy resins with a high glass transition temperature (T_g), used in carbon fiber/epoxy composites for aerospace applications. Conventional toughening methods rely on adding toughening agents, often compromising the processibility and thermal stability. This study introduces a simple self-toughening approach that enhances the fracture toughness without sacrificing other properties by controlling the cured epoxy network structure. Tetraglycidyl 4,4'-diaminodiphenylmethane (TGDDM) epoxy resin was cured using mixtures of structural isomeric curing agents, 3,3'- and 4,4'-diaminodiphenyl sulfone (3,3'- and 4,4'-DDS), at ratios of 7:3, 5:5, and 3:7. The optimal 7:3 ratio produced a resin with 30% higher fracture toughness compared to TGDDM/3,3'-DDS and 100% higher than the TGDDM/4,4'-DDS system. The T_g of the self-toughened resin ranged from 241 to 266 °C, which was intermediate between the T_g values of the TGDDM/3,3'-DDS and TGDDM/4,4'-DDS systems. This improvement is attributed to the higher crosslink density and reduced free volume of the epoxy network. These findings demonstrate that simply mixing isomeric curing agents enables self-toughening, providing a practical and efficient strategy to enhance the performance of high-T_g epoxy resins in advanced composite applications.PolymersSelf-Toughened Epoxy Resin via Hybridization of Structural Isomeric Curing Agents.PMC1190246822-CM-CO-19No. 22-CM-19Jeong ECheon JJeong HJLee SGWon JSKim BJKwon WLee MYfalseSelf-Toughened Epoxy Resin via Hybridization of Structural Isomeric Curing Agents.Fracture toughness is a key property of epoxy resins with a high glass transition temperature (T_g), used in carbon fiber/epoxy composites for aerospace applications. Conventional toughening methods rely on adding toughening agents, often compromising the processibility and thermal stability. This study introduces a simple self-toughening approach that enhances the fracture toughness without sacrificing other properties by controlling the cured epoxy network structure. Tetraglycidyl 4,4'-diaminodiphenylmethane (TGDDM) epoxy resin was cured using mixtures of structural isomeric curing agents, 3,3'- and 4,4'-diaminodiphenyl sulfone (3,3'- and 4,4'-DDS), at ratios of 7:3, 5:5, and 3:7. The optimal 7:3 ratio produced a resin with 30% higher fracture toughness compared to TGDDM/3,3'-DDS and 100% higher than the TGDDM/4,4'-DDS system. The T_g of the self-toughened resin ranged from 241 to 266 °C, which was intermediate between the T_g values of the TGDDM/3,3'-DDS and TGDDM/4,4'-DDS systems. This improvement is attributed to the higher crosslink density and reduced free volume of the epoxy network. These findings demonstrate that simply mixing isomeric curing agents enables self-toughening, providing a practical and efficient strategy to enhance the performance of high-T_g epoxy resins in advanced composite applications.2025-01-01T00:00:00Z2025 Mar2025-04-04T01:28:25.521Z2025-04-04T01:28:25.521ZS-EPMC119024684007618710.3390/polym17050695