Synergistic Curing Of Diallyl-Bearing Epoxy Resin/Etramethylthiuram Disulfide

Diglycidyl ether of2,2’-diallyl bisphenol A (DADGEBA) is a novel bifunctional epoxy resin, which has two reactive functional groups-epoxy and allyl groups. DADGEBA can realize dual-curing with a suitable curing agent. Tetramethylthiuram disulfide (TMTD), a common vulcanizing agent, was used as a curing agent to react with DADGEBA in this paper. The curing mechanism, curing behavior and cured performance of DADGEBA/TMTD system were studied further.The active functional group of diglycidyl ether of bisphenol A(E51) is just epoxy group, and compared to DADGEBA, the chemical structure of E51is just less two allyl groups. There is a comparative study between E51/TMTD system with DADGEBA/TMTD system. It is comfirmed that the curing mechanism of E51/TMTD and DADGEBA/TMTD is different by the gel time test and DSC exotherm curve analysis of different systems. Curing of E51/TMTD was studied by Fourier transform infrared spectroscopy (FTIR), and it is found the epoxy groups contects reduced and ether bonds contects increased. It is deduced that the curing mechanism of E51/TMTD is anionic polymerization caused by tertiary amine.Curing of DADGEBA with TMTD was investigated by differential scanning calorimetry (DSC) and FTIR. Exotherms were observed in DSC curves, and the vinyl and epoxy groups contents reduced with the increase of time by FTIR measurement when the DADGEBA/TMTD mixture was heated.’H-NMR was adopted to monitor the mercapto groups in diallyl bisphenol A (DABPA)/TMTD reaction. Mass spectrum was used to detect the molecular weight and their structures formed. Based on the experimental results, the conclusion was drawn that the curing mechanism of DADGEBA/TMTD is a synergistic curing reaction: first, TMTD can cleavage into sulfur radicals at high temperature; then, the a-H of allyl groups can be captured by some sulfur radicals to form mercapto groups and the radicals are transferred to allyl structures, and the other sulfur radicals initiate addition reaction of vinyl groups; finally, resultant mercapto groups react further with epoxy groups through ring-opening reaction. Meanwhile, coupling reactions between different radicals occur.The curing reaction kinetics of E51/TMTD and DADGEBA/TMTD were studied by non-isothermal DSC. The curing processes of different systems were calculated by extrapolation method. The synergistic curing mechanism DADGEBA/TMTD system is consistent with two-step reaction.The cured resins of E51/TMTD and DADGEBA/TMTD systems are brittle. The toughening modification of the systems is studied by blending with reactive liquid rubber, epoxy-terminated butadiene acrylonitrile rubbers (ETBN) in this paper. The bonding strength, mechanical properties and thermal performance of the two systems were tested, and it is concluded that the bonding strenghth of DADGEBA/TMTD is better, the mechanical properties of E51/TMTD system are better, the glass transition of the two systems are decreased, and the thermal decomposition temperature of the two systems are not decreased.