Investigation of Microstructure and Reagents Ratio on the Properties and Structure of Nitrated Hydroxyl Terminated Polybutadiene (Nitro-HTPB)

Hydroxyl-terminated polybutadiene (HTPB) has been widely used as a binder for energetic composites. This neutral binder contains 10 to 15% by weight of these compounds, which if energized, increase the energy content and maintain the physical and chemical properties of the original HTPB to a large extent. The binding of Nitro to the main chain of HTPB (nitration) is a good way to energize it. Nitration common methods, such as nitration with a mixture of acids, dinitrogen pentoxide, and nitromercuration- demercuration, have led to the destruction of the backbone of the polymer. In this research, Nitration with nitrile iodide reagent has been used for the functionalization of HTPB with nitro groups, in which the double bonds and the backbone of resin are not degraded. In order to maintain the unique physical and chemical properties of HTPB, nitration levels are limited to 10 to 15% of double bonds. The purpose of this research was to investigate the effect of HTPB resin structure and the ratio of reactants used on the HTPB nitration process. For this purpose, four samples of nitrated Hydroxyl-terminated polybutadiene (Nitro-HTPB) were synthesized from two different types of HTPB with different characteristics and using two different proportions of the reactants. Then, samples were characterized by FT-IR and 1HNMR tests, and parameters such as percentage of nitration, microstructure, and their rheological behavior were compared. The results showed that the nitration rate of the synthetic samples was influenced by the ratio of the reactant used and the percentage of trans-microstructure of the initial HTPB resin. Also, samples with higher nitration content have higher viscosity and less pot life. Considering all the parameters, it can be claimed that NHA1 resin with 12.2% nitro content among synthesized resins (among 3.1, 4.1, 12.2, and 17.6%) has the potential to be used as a binder in energetic composites.