1-Methyl-4-R-1,2,4-triazolium (R = -CH 2 CH 2 OCH 3 , -CH 2 COOCH 2 CH 3 )-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 ), 1-methyl-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 ( T m , -72.60 to -32.67 °C) and good thermal stability ( T d , 161-348 °C) and are suitable as plasticizers for hydroxyl-terminated polybutadiene (HTPB) curing systems. Among these four ionic liquids, ester-functionalized cations can help to improve the tensile strength ( 2a , 0.943 MPa; 2b , 1.113 MPa) of the cured system, while ether-functionalized 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 NO 3 - is higher, while that of HTPB elastomers containing NTf 2 - 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/m 3 , 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.