Ferrocene-based polyethyleneimines for burning rate catalysts

Abstract

Ferrocene-based polymers and their derivatives have the ability to catalyze the burning process of composite solid propellants efficiently. However, the simple and volatile ferrocene migrates to the surface of the solid propellant on prolonged storage, which alters the designed burning parameters and more seriously causes unexpected explosions. To retard migration problems, six novel 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 using ¹H NMR, FT-IR and UV-Vis spectroscopy. The redox properties of the polymers are very important for burning rate catalysts (BRCs). Cyclic voltammetry (CV) revealed that all the PEI-Fcs showed redox properties due to the presence of ferrocene moieties. Migration studies confirmed that the migration of these PEI-Fcs was much slower than that of 2,2-bis(ethylferrocenyl)propane (catocene) and ferrocene. The catalytic effect of PEI-Fcs on the thermal decomposition of ammonium perchlorate (AP) was investigated using thermogravimetry (TG) and differential thermogravimetry (DTG). It was found that in the presence of PEI-Fcs (1–6), the peak decomposition temperature of AP was shifted towards the left (decreased) significantly. The results from the TG and DTG analysis indicated that the novel PEI-Fcs had good catalytic effects of lowering the thermal decomposition temperature of AP and were almost stable up to 220 °C. We expect that these novel PEI-Fcs would have great value as high BRCs for composite solid propellants.