1-Methyl-4-R-1,2,4-triazolium (R =-CH2CH2OCH3,-CH2COOCH2CH3)-Based Ionic Liquids as Plasticizers for Solid Propellants

In this paper, a series of energetic ionic liquid plasticizers of 1-methyl-4-methoxyethyl-1,2,4-triazolium chloride (1), 1methyl-4-methoxyethyl-1,2,4-triazolium bis(trifluoromethylsulfonyl)imide (1a), 1-methyl-4-methoxyethyl-1,2,4-triazolium nitrate (1b), 1-methyl-4-ethyl acetate-1,2,4-triazolium chloride (2), 1-methyl-4-ethyl acetate-1,2,4-triazolium bis(trifluoromethylsulfonyl)imide (2a), and 1-methyl-4-ethyl acetate-1,2,4-triazolium nitrate (2b) were synthesized and characterized. The results show that compounds 1a, 1b, 2a, and 2b have lower melting points (Tm, -72.60 to -32.67 degrees C) and good thermal stability (Td, 161-348 degrees C) and are suitable as plasticizers for hydroxyl-terminated polybutadiene (HTPB) curing systems. Among these four ionic liquids, esterfunctionalized cations can help to improve the tensile strength (2a, 0.943 MPa; 2b, 1.113 MPa) of the cured system, while etherfunctionalized cations are more beneficial to improve elongation at break (1a, 522.90%; 1b, 484.45%). Ester-functionalized ionic liquids are more beneficial to reduce the glass transition temperature of HTPB elastomers. The storage modulus of HTPB elastomers containing NO3- is higher, while that of HTPB elastomers containing NTf2- is lower. The crosslink densities of HTPB/TDI/2a and HTPB/TDI/2b plasticized by ester-functionalized ionic liquids are larger, which are 9369 and 9616 mol/m3, respectively. There are hydrogen bond interactions between the ionic liquid and the HTPB elastomer, and these interactions changed the distribution of the hard and soft segments in the polymer molecules.

Automated summary

This paper synthesized and characterized a series of energetic ionic liquid plasticizers. The results showed that these compounds, particularly the ester-functionalized cations, were suitable as plasticizers for hydroxyl-terminated polybutadiene (HTPB) curing systems, improving the tensile strength and elongation at break. The ester-functionalized ionic liquids also reduced the glass transition temperature of HTPB elastomers, and the storage modulus varied depending on the anions present. The crosslink densities of HTPB/TDI/2a and HTPB/TDI/2b plasticized by ester-functionalized ionic liquids were larger.