Hexahydrotriazine derivative containing imidazole for fast curing, improved mechanical strength, and flame retardancy of epoxy

Abstract

We synthesized a hexahydrotriazine derivative containing imidazole, 1,3,5‐tris[4′‐(1H‐imidazol‐1‐yl)‐(1,1′‐biphenyl)‐4‐yl]‐1,3,5‐triazinane (HIM) and adapted it as a co‐curing agent for epoxy resin (EP). The curing kinetics of HIM were evaluated using elevated differential scanning calorimetry (DSC) analysis, and the curing speed was determined to be accelerated with HIM. Moreover, when 5 phr of HIM was applied to the epoxy system, the tensile strength of cured EP increased to 50.9 MPa. Because of the high nitrogen content of HIM, when the candidate amount of HIM was increased, the char yield increased. HIM (20 phr) showed a char yield of 36.1%, which is about 74% higher than that of the HIM (0 phr) reference (20.7%). The char layer acts as a barrier between oxygen and polymeric decomposition gases, inducing a high flame‐retardant property.

Imidazole substituted benzothiadiazole derivatives as latent curing agent for epoxy thermosetting resin

“…1 H NMR spectrum of BTD‐MZ 2 is shown in Figure 2. The results of 1 H NMR showed that the three characteristic peaks were 6.40 (2 H), 7.21 (2 H) and 7.23 ppm (2 H), respectively, representing H on imidazole heterocyclic ring 29 and 7.75 ppm (2 H) representing H on BTD. Based on the above analysis, we successfully synthesized BTD‐MZ 2 36 …”

“…However, when the content of BTD‐MZ 2 continues to increase to 20 wt%, the residual carbon rate decreases. This is because when the content of the resin matrix remains unchanged, adding an excessive amount of BTD‐MZ 2 to the resin alone is equivalent to doping, which will cause the dispersion of BTD‐MZ 2 in the resin to deteriorate and cause defects in the EP matrix 28,29 …”

“…This is because when the content of the resin matrix remains unchanged, adding an excessive amount of BTD-MZ 2 to the resin alone is equivalent to doping, which will cause the dispersion of BTD-MZ 2 in the resin to deteriorate and cause defects in the EP matrix. 28,29 3.4 | Rheology behavior of EP/xwt% BTD-MZ 2 and EP/7.2 wt% 2E4MMZ…”

“…Therefore, latent curing agent was developed to overcome the storage stability and rapid curing of onecomponent EP curing system. 23,[27][28][29][30][31][32][33] So far, encapsulation of the imidazole derivatives and introduction of inhibitory activity group into the position 1 of imidazole have been proven as efficient methods for developing imidazole-based latent curing agents. Xing et al 34 prepared a spherical latent microcapsule curing agent, curing reaction in 3 h to complete, as long as 100 days of storage time at room temperature.…”

“…In addition, shortening the curing period of thermosetting resin is also the key to manufacture resin matrix composites efficiently. Therefore, latent curing agent was developed to overcome the storage stability and rapid curing of one‐component EP curing system 23,27–33 . So far, encapsulation of the imidazole derivatives and introduction of inhibitory activity group into the position 1 of imidazole have been proven as efficient methods for developing imidazole‐based latent curing agents.…”