Synthesis And Evaluating The Deblocking And Curing Performance Of Isocyanate Modified Imidazole Using As Harderner

Imidazole compounds is a very important kind of curing agent used for epoxy resin. Imidazole has high reactivity at middle temperature and low toxicity and the resin system with imidazole exhibits excellent mechanical properties after curing process. However, there are obvious disadvantages for unmodified imidazole, such as mostly solid at room temperature and difficult mixture with epoxy resin, a certain amount of volatile at high temperature, short shelf life of resin system etc. To overcome these defects of imidazole and take full advantages of it, chemical modification is a feasible and scientific way. Isocyanate is an effective kind of modifier.In this paper, hexamethylene diisocyanate(HDI), trimethylhexamethylene diisocyanate (TMHDI) and diphenyl methane diisocyanate (MDI) were used to synthesis three kinds of isocyanate modified 2E4MI with high structure purity as curing agent successfully. And on this basis we systematically studied the deblocking and curing performance of the synthesized isocyanate modified 2E4MI and found the relationship between their structure and fundamental properties of epoxy resin to provide data support and theory guidance on making high performance imidazoles curing agent.The results of TG, hot-stage FTIR and simultaneous TG-DSC showed that the thermal stability of isocyanate modified 2E4MI decreased in the following order:MDI-2E4MI>HDI-2E4MI>TMHDI-2E4MI and all isocyanate modified 2E4MI showed two steps deblocking behavior. HDI-2E4MI and TMHDI-2E4MI2 went through melting process before deblocking, however MDI-2E4MI deblocked directly without melting. Then we studied the curing performance of three kinds of isocyanate modified 2E4MI and found that there were two different curing mechanisms. MDI-2E4MI had highest curing activity and went through only one step curing. For HDI-2E4MI and TMHDI-2E4MI, there were three curing steps. The first step curing was the reaction between 2E4MI from the first step deblocking and epoxy resin. The second step curing was the reaction between isocyanate from the first step deblocking and hydroxyl group generated by the first step curing. The third step curing was that 2E4MI and isocyanate from the second step deblocking reacted with epoxy resin together. The curing rate of HDI-2E4MI was lower than that of TMHDI-2E4MI in the initial stage (?<0.1), then exceeded because HDI started to take part in curing process. The activation energy of HDI-2E4MI had a higher starting point at a=0.1 and then was lower than that of TMHDI-2E4MI. As a whole, the activation energy of MDI-2E4MI decreased slowly with the increase of degree of curing, however the activation energy of HDI-2E4MI and TMHDI-2E4MI increased gradually.Finally we systematically studied the relationship between the structure and cured products fundamental performance of three kinds of isocyanate modified 2E4MI/AFG90 systems. The results showed that storage modulus, tensile modulus, flexural modulus, glass transition temperature and vicat softening temperature of the cured resin systems decreased in the following order:MDI-2E4MI/AFG90>TMHDI-2E4MI/AFG90>HDI-2E4MI/AFG90. The trend was in accordance with the stiffness trend of three kinds of isocyanate.