Study On Synthesis,Anti-migration Properties And Burning Rate Catalytic Properties Of Ferrocene-based Branched Compounds

To overcome force of gravity and to fly in the sky, different ways like use of fire balloons, planes, helicopters, rockets, etc. have been discovered. Among different ways, rockets are the fastest way to overcome force of gravity with excellent efficiency. One of the important components that provide driving force to the rocket is the composite solid propellant. Composite solid propellants are the energy sources, which are used in rocket motors for the propulsion of launch vehicles. Usually, composite solid propellant with reduced smoke and excellent burning rate is consisted of an inorganic oxidizer (ammonium perchlorate) (AP), metallic fuel (aluminum) (Al), binder (hydroxyl terminated polybutadiene) (HTPB) and the small amount of other constituents such as, plasticizer, curing agent, stabilizer and burning rate catalysts (BRCs). The characteristics of an excellent composite solid propellant should be low-pressure exponents and stable burning rate. With the development in science and technology, development of high performance composite solid propellant is a growing concern. Generally, there are two approaches to get high efficient composite solid propellant. One approach is to develop a new composite solid propellant and another approach is to improve formulation of the conventional composite solid propellant without changing its composition. Second approach is relatively easy and quick. The commonly used methods to improve the conventional solid propellant formulation include adjustment of size of the main fuel such as use of Al powder, ultrafine nanoscale AP, adjustment of adhesive system (binding agent) and use of BRCs.There are two ways to enhance performance of the composite solid propellant. One approach is the use of BRCs in the composite solid propellant and other approach is the use of high performance binding agent. The addition of efficient BRCs in the composite solid propellant improves instantaneous combustion of the composite solid propellant and facilitates smooth burning, while the addition of an efficient binding agent improves mechanical properties of the adhesive system. Therefore, a promising method to enhance performance of the composite solid propellant is the use of efficient BRCs in the composite solid propellant. The addition of BRCs in the solid propellant changes pressure exponent of the propellant, reduces sensitivity to temperature and pressure, improves ignition performance and combustion stability of the composite solid propellant and adjusts burning rate to achieve the desired engine design thrust.Various kinds of BRCs such as transition metal oxides, nanometal particles, metal chelates and ferrocene-based BRCs have been used to enhance burning rate of the composite solid propellants. Among all BRCs, ferrocene-based BRCs are the most commonly used BRCs for the composite solid propellant due to their better ignitability in the propellant, microscopic homogeneities in distribution and good compatibility with organic binder. Ferrocene-based compounds, polymers and numerous derivatives have attracted much attention of the scientists as ferrocene-based BRCs due to their reversible redox behavior, high thermal stability and their chemical modification possibilities. Burning rate performance of the ferrocene-based BRCs depends on their chemical structures, solubility, molecular mobility and effective iron contents. Ferrocene-based BRCs also show extraordinary effect on burning rate of HTPB propellant containing AP and powder Al, which are the most commonly used oxidizing agent and metallic fuel, respectively. On combustion of ferrocene-based compounds, polymers, dendrimers and derivatives, ferrocene moieties change into nanoscale hematite particles. These produced nanoscale hematite particles possess large surface area and show better performance in increasing burning rate of the composite solid propellant in comparison with powder hematite.Ferrocene, simple ferrocene-based compounds and numerous derivatives are versatile/ migrate easily. When ferrocene-based BRCs are stored in the composite solid propellant, ferrocene and simple ferrocene-based compounds result in the worsening of the composite solid propellant during burning process and become sensitive to electric discharge. These drawbacks lead to poor aging, unstable combustion, increase in mechanical sensitivity toward pressure and temperature, change in designed burning parameters and irreproducible properties of the composite solid propellant, which reduce service life.In order to overcome migration problems of ferrocene-based BRCs, much attention has been paid to improve efficiency of ferrocene-based BRCs. The migration problems of ferrocene-based BRCs can be overcome by extending length of carbon chain on ferrocene ring, introducing polar elements like oxygen and nitrogen which make ferrocene-based BRCs polar, introducing reactive groups in ferrocene ring such as epoxide,-OH,-NH2,-NCO, etc., introducing inorganic groups in ferrocene ring and synthesizing high molecular weight ferrocene-based dendrimers with special topology and containing large number of polar elements like oxygen and nitrogen.A lot of work has been done to synthesize ferrocene-based BRCs but migration problems still exist. Ferrocene-based BRCs with polar elements have been synthesized but such synthesized ferrocene-based BRCs still showed obvious migration on prolong storage. Therefore, study on migration problems of ferrocene-based BRCs is still being continued to find cheap and efficient way to avoid these problems. In our projects, we designed ferrocene-based BRCs (ferrocene-based polymers, compounds and dendrimers) containing large number of oxygen and-NH groups. Incorporation of ferrocene into dendrimers is a challenge of growing interest for the researchers. Such ferrocene-based dendrimers have distinctive redox properties of ferrocene with low viscosity, high molecular weight and high thermal stability. It has been found that grafting of ferrocene on the dendrimers is the one of the effective ways to overcome migration problems of the ferrocene-based BRCs in the composite solid propellant. The presence of oxygen and nitrogen in the ferrocene-based BRCs made them polar, which resulted in the dipole-dipole interactions between ferrocene-based BRCs and AP. The presence of -NH groups resulted in strong hydrogen bonding of these ferrocene-based BRCs with AP and also with binding agent. The formation of strong hydrogen bonding and dipole-dipole interactions resulted in excellent anti-migration properties of ferrocene-based BRCs. AP is the most commonly used inorganic oxidizer in AP-based propellant due to its excellent burning characteristics, good processability and storability. It has been found that combustion performance of AP-based propellant is directly influenced by thermal decomposition of AP. Therefore, thermal decomposition of AP can be accelerated by the addition of ferrocene-based BRCs in AP-based propellant and burning rate catalytic performance of BRCs can be assessed on thermal decomposition of AP.In first project, to overcome migration problems of ferrocene-based BRCs and to enhance burning rate of the composite solid propellant, six ferrocene-based polyethyleneimines (PEI-Fcs) were synthesized by the condensation reaction of branched polyethyleneimine (PEI) with ferrocenecarbonyl chloride. The structures of the synthesized PEI-Fcs were characterized by nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) spectroscopy. Ultraviolet-visible (UV-Vis) absorption studies indicated that PEI-Fc-4 to PEI-Fc-6 showed significant photo-induced charge transfer effect. It was found that with the increase in ferrocene in PEI-Fcs, photo-induced charge transfer effect become more significant. As relatively large number of ferrocene was present in PEI-Fc-6, so it showed more prominent photo-induced charge transfer effect. Several burning rate catalytic mechanisms have been proposed to explain catalytic decomposition of AP catalyzed by ferrocene-based BRCs but electron transfer mechanism is preferred over other mechanisms. Electrochemical properties of the ferrocene-based BRCs are important to investigate their potential application as ferrocene-based BRCs. The combustion process of PEI-Fcs in the composite solid propellant can be studied by studying their electrochemical properties. Among different methods of electrochemical measurements, cyclic voltammetry (CV) is considered as a best method. Therefore, the electrochemical properties of the synthesized PEI-Fcs were investigated by CV. It was found that PEI-Fcs showed redox properties due to the presence of ferrocene and the electrode processes were diffusion controlled over the detected scan range. The effect of solvent and potential scan rate on the electrochemical properties of PEI-Fcs was also investigated. It was found that CV curves of PEI-Fcs were affected by solvent polarity and also by potential scan rate. The increase in polarity of the solvent resulted in the deformation of the peaks shape. Additionally, peak current values of PEI-Fcs (IPA and IPC) were increased with the increase in potential scan rate. Furthermore, the rate of increase in the reduction peak current (IPC) was higher than the rate of increase in the oxidation peak current (IPA). Although, the electrode processes were diffusion controlled, but rate of electron transport between PEI-Fcs and electrodes and electrode reactions were slow. In addition, peak potential in reversible electrode process is independent on the scan rate and peak-to-peak separation (△Ep) is less than 60 mV, while in case of irreversible electrode process, △Ep is more than 60 mV. It can be concluded that the electrochemical processes of PEI-Fcs were neither simple reversible nor totally irreversible. Anti-migration studies confirmed that the migration of PEI-Fcs was much slower than most commonly used ferrocene-based burning rate catalyst,2,2-bis(ethyl ferrocenyl)propane (catocene). The excellent anti-migration behavior of PEI-Fcs was due to the presence of large number of oxygen and nitrogen, which resulted in the interactions of PEI-Fcs with AP and also with binding agent and low vapor pressure due to high molecular weight. Among PEI-Fcs, PEI-Fc-1 showed excellent anti-migration behavior. The excellent anti-migration behavior of PEI-Fc-1 was due to the presence of relative small number of ferrocene. Thermal stability and burning rate catalytic effect of PEI-Fcs on the thermal decomposition of AP was investigated by using thermogravimetry (TG) and differential thermogravimetry (DTG) techniques. It was found that in the presence of 5 wt.% PEI-Fcs, thermal decomposition temperature of AP was significantly decreased. Among PEI-Fcs, PEI-Fc-6 showed excellent burning rate catalytic activity on thermal decomposition of AP and it decreased thermal decomposition temperature of AP form 406.42℃ to 307.17℃. The excellent burning rate catalytic activity of PEI-Fc-6 was due to the presence of relative large number of ferrocene. The burning rate catalytic properties of PEI-Fc-6 were also investigated by changing wt.%(1-5) of PEI-Fc-6. It was found that with the increase in the concentration of PEI-Fc-6, thermal decomposition temperature of AP was significantly decreased. TG and DTG analysis showed that PEI-Fcs have good catalytic effect on thermal decomposition of AP and were almost stable up to 220℃. On the basis of experimental results, it was concluded that PEI-Fcs have great value as excellent BRCs for the composite solid propellant due to their redox behavior, thermal stability, excellent anti-migration and burning rate catalytic properties.In second project, eleven ferrocene-based compounds (1-11) as ferrocene-based BRCs were synthesized by the condensation reaction of ferrocenecarbonyl chloride with corresponding amines and alcohols to investigate the effect of polar elements like oxygen and nitrogen on anti-migration behavior of small ferrocene-based compounds. The synthesis of 1-11 was confirmed by 1H NMR and FT-IR spectroscopy. UV-Vis absorption studies showed that all the synthesized ferrocene-based compounds showed photo-induced charge transfer effect and it was more prominent in multinuclear ferrocene-based compounds. The electrochemical properties of 1-11 were analyzed by CV. The effect of solvent and potential scan rate on the CV curves of 1-11 was also investigated. It was found that CV curves of 1-11 were affected by solvent polarity and potential scan rate. The increase in polarity of the solvent resulted in the deformation of the peaks shape. Additionally, the peak current values (IPA and IPC) of 1-11 were increased with the increase in potential scan rate. Furthermore, the rate of increase in oxidation peak current (IPC) was higher than the rate of increase in reduction peak current (IPA).1-11 showed reversible redox behavior due to the presence of ferrocene and electrode processes were diffusion controlled over the detected scan range. Anti-migration studies showed that migration of 1-11 was slower than catocene and ferrocene due to formation of dipole-dipole interactions and hydrogen bonding with AP and binder. Oxygen-containing compounds showed better anti-migration behavior than nitrogen-containing compounds. Thermal stability and catalytic behavior of 1-11 on thermal decomposition of AP was investigated by TG and DTG techniques. It was found that almost all the synthesized compounds were thermally stable up to 230℃. In the presence of 5 wt.% of 1-11, thermal decomposition temperature of AP was significantly decreased. Among 1-11,11 showed excellent burning rate catalytic activity on thermal decomposition of AP and in the presence of 5 wt.%11, thermal decomposition temperature of AP was decreased to 317.06℃. TG and DTG analysis showed that 1-11 have good catalytic effect on thermal decomposition of AP. Oxygen-containing compounds showed much slower migration and better burning rate catalytic activity on thermal decomposition of AP than nitrogen-containing compounds.In third project, zero to third generation ethylene diamine-based ferrocene terminated dendrimers (0G,1G,2G and 3G) were synthesized by the Michael addition reaction followed by the reaction with ethylene diamine and then by the condensation reaction of amine-terminated dendrimers with ferrocenecarbonyl chloride. In first step,0.5G, 1.5G and 2.5G were synthesized by the Michael addition reaction of ethylene diamine, 0.75G and 1.75G with methyl acrylate. In second step,0.75G,1.75G and 2.75G were synthesized by the reaction of 0.5G,1.5G and 2.5G with ethylene diamine. In third step,0G,1G,2G and 3G were synthesized by the condensation reaction of ethylene diamine,0.75G,1.75G and 2.75G with ferrocenecarbonyl chloride. The synthesis of 0G,1G,2G and 3G was confirmed by 1H NMR and FT-IR spectroscopy. UV-Vis absorption studies indicated that 2G and 3G showed photo-induced charge transfer effect and it was more prominent in 3G due to the presence of relative large number of ferrocene. The electrochemical properties of 0G,1G,2G and 3G were analyzed by CV. It was found that these ferrocene terminated dendrimers showed redox behavior due to the presence of ferrocene. The effect of solvent and potential scan rate on electrochemical behavior of 0G,1G,2G and 3G was also investigated. It was found that electrochemical behavior of0OG,1G,2G and 3G was affected by solvent polarity and potential scan rate. The increase in polarity of the solvent resulted in the deformation of the peaks shape. Additionally, the peak current values (IPA and IPC) of 0G,1G and 2G were increased with the increase in the potential scan rate. Furthermore, the rate of increase in the reduction peak current (IPC) was higher than the rate of oxidation peak current (IPA). It was also found that redox processes of these dendrimers were diffusion controlled. Although, the electrode processes were diffusion controlled, but. rate of electron transport between these ferrocene terminated dendrimers and electrodes and electrode reactions were slow. It can be concluded that the electrochemical processes of 0G,1G,2G and 3G were neither reversible nor totally irreversible. Anti-migration studies indicated that 1G,2G and 3G showed excellent anti-migration properties in AP-based propellant than catocene and ferrocene. The excellent anti-migration behavior of 1G,2G and 3G was due to formation of strong hydrogen bonding and dipole-dipole interactions of 1G,2G and 3G with AP and also with binding agent due to the presence of large number of-NH groups and oxygen, respectively. Among 1G,2G and 3G,1G showed excellent anti-migration properties due to the presence of relatively small number of ferrocene. Thermal stability and burning rate catalytic effect of OG,1G,2G and 3G on thermal decomposition of AP was investigated using TG and DTG techniques. It was found that OG,1G,2G and 3G were almost stable up to 260℃. TG and DTG analysis showed that OG,1G,2G and 3G have good catalytic effect on lowering thermal decomposition temperature of AP. In case of 3G, thermal decomposition of AP was decreased to 327.02℃. Therefore, these dendrimers can be used as ferrocene-based BRCs for AP-based propellant due to their high thermal stability, redox behavior, excellent anti-migration and burning rate catalytic activity.In fourth project, zero to second generation tris(2-aminoethyl)amine-based ferrocene terminated dendrimers (GO, Gl and G2) were synthesized by the Michael addition reaction followed by the reaction with ethylene diamine and then by the condensation reaction of amine-terminated dendrimers with ferrocenecarbonyl chloride. In first step, G0.5 and G1.5 were synthesized by the Michael addition reaction of tris(2-aminoethyl)amine and G0.75 with methyl acrylate. In second step, G0.75 and G1.75 were synthesized by the reaction of G0.5 and G1.5 with ethylene diamine. In third step, G0, G1 and G2 were synthesized by the condensation reaction of tris(2-aminoethyl)amine, G0.75 and G1.75 with ferrocenecarbonyl chloride. The structures of G0, G1 and G2 were confirmed by 1H NMR and FT-IR spectroscopy. UV-Vis absorption studies indicated that Gl and G2 showed photo-induced charge transfer effect. The electrochemical behavior of G0, G1 and G2 was investigated by CV. It was found that G0, G1 and G2 showed redox behavior due to the presence of ferrocene. The effect of solvent and potential scan rate on electrochemical behavior of G0, G1 and G2 was also investigated. The increase in polarity of the solvent resulted in the deformation of the peaks shape. Additionally, peak current values (IPA and IPC) of G0, Gl and G2 were increased with the increase in the potential scan rate. Furthermore, the rate of increase in the reduction peak current (IPC) was higher than the rate of oxidation peak current (IPA). It was found that electrochemical behavior of G0, G1 and G2 was affected by solvent polarity and potential scan rate. It was concluded that redox processes of G0, G1 and G2 were diffusion controlled over the detected scan range and were neither totally reversible nor simply irreversible. Anti-migration studies showed that migration of G0, G1 and G2 was much slower than catocene and ferrocene. The excellent anti-migration behavior of G0, G1 and G2 was due to the presence of large number of oxygen and-NH groups, which are responsible for the formation of dipole-dipole interactions and strong hydrogen bonding of GO, Gl and G2 with AP and also with binding agent, respectively. Thermal stability and burning rate catalytic effect of G0, G1 and G2 on thermal decomposition of AP was investigated by TG and DTG techniques. It was found that G0, G1 and G2 were thermally stable up to 265℃. It was observed that G0, G1 and G2 showed good catalytic effect on thermal decomposition temperature of AP. Among G0, G1 and G2, G2 showed excellent burning rate catalytic activity and thermal decomposition of AP was decreased to 328.57℃. So, these tris(2-aminoethyl)amine-based ferrocene terminated dendrimers can be used as ferrocene-based BRCs for AP-based propellant due to their high thermal stability, redox behavior, excellent anti-migration and burning rate catalytic activity.On the basis of experimental findings, it was concluded that ferrocene-based branched compounds containing large number of polar elements like oxygen and nitrogen can be used as ferrocene-based BRCs for AP-based propellant due to their excellent anti-migration and burning rate catalytic properties.