Catalyst-free synthesis of isocyanate-blocked imidazole and its use as high-performance latent hardener for epoxy resin
- PDF / 3,007,473 Bytes
- 21 Pages / 595.276 x 790.866 pts Page_size
- 10 Downloads / 175 Views
Catalyst-free synthesis of isocyanate-blocked imidazole and its use as high-performance latent hardener for epoxy resin Hefeng Li1, Cong Liu1, Xiaole Zhang1, Ke Shi1, Xianhua Huan1, Song Lin3, Sibao Wu1, Xiaolong Jia1,2,*, Qing Cai1, and Xiaoping Yang1,2 1
State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China 2 Key Laboratory of Carbon Fiber and Functional Polymer, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China 3 North China Institute of Aerospace Engineering, Langfang 065000, People’s Republic of China
Received: 19 June 2020
ABSTRACT
Accepted: 7 September 2020
Catalyst-free synthesis in three kinds of isocyanate-blocked imidazole compound was successfully achieved by chemically connecting 2-ethyl-4methylimidazole (2E4MI) with hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI) or 4,40 -diphenylmethane diisocyanate (MDI), which were tested as the latent hardeners for epoxy (EP) resins. The chemical structures of the synthesized HDI-2E4MI, TMHDI-2E4MI and MDI2E4MI were identified with Fourier transform infrared spectroscope (FTIR), 1H and 13C nuclear magnetic resonance (1H NMR and 13C NMR). Based on characterizations including thermogravimetry/differential scanning calorimetry (TG/DSC) simultaneous testing and hot-stage FTIR, it was found that both HDI2E4MI and TMHDI-2E4MI exhibited two-step deblocking behavior, whereas the deblocking process of MDI-2E4MI was completed only via one step. Curing kinetics of HDI-2E4MI/EP, TMHDI-2E4MI/EP and MDI-2E4MI/EP systems were then studied by non-isothermal DSC using Kissinger model. The results revealed that MDI-2E4MI/EP system could be cured via a two-step reaction with the highest curing rate due to the high reactivity of MDI-2E4MI, which was much different from the four-step curing behaviors of both HDI-2E4MI/EP and TMHDI-2E4MI/EP systems. Compared to the reference 2E4MI, noticeably, the three synthesized hardeners showed the outstanding latent features with lower curing activity and longer shelf life and the EP systems cured by the hardeners exhibited desirable mechanical properties and thermal stability. This study provided a feasible approach to synthesize high-performance imidazole-based
Ó
Springer Science+Business
Media, LLC, part of Springer Nature 2020
Handling Editor: Gregory Rutledge.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05331-w
J Mater Sci
latent hardener for wide practical applications in a greenway via the blocking treatment through tailoring the isocyanate structure.
Introduction Epoxy (EP) resins have been increasingly applied in advanced technological fields including bonding adhesives, coatings, encapsulations, prepregs, laminates and fiber-reinforced composites, due to their excellent physical and chemical properties of high specific strength, good thermal characteristics and corrosion resistance, low shrinkage during
Data Loading...
