Synthesis and characterization of iron carbonyl-modified hydroxyl-terminated polybutadiene: A catalyst-bound propellant binder for burn-rate augmentation

Iron was coordinately linked to the hydroxyl-terminated polybutadiene (HTPB) backbone using iron carbonyl via a ligand displacement reaction. The modified HTPB thus obtained was reddish brown in color and was characterized by GPC, FTIR, NMR, thermal, and propellant studies. No significant changes in the rheology, molecular weight, and molecular weight distribution were seen in the modified resin when the bonded Fe content was >0.8.0 wt %. However, the hydroxyl value of the resin decreased by 3-7 irrespective of the weight percent of the bonded Fe, and this was more likely due to the Fe-catalyzed oxidation of the -CH2OH moiety, mostly to the -CHO group. Apparently, this has not affected the cure characteristics of the binder, as demonstrated by the good mechanical properties of the gum stock and the propellant. The catalytic efficiency of the bonded Fe on the burn rate of the propellant was more efficient than was the free Fe added to the propellant. The aging characteristics of the resin for the bound iron content of less than or equal to0.8 wt % was apparently good, as its viscosity and molecular weight did not undergo any drastic changes even after 18 months' storage under ambient conditions. (C) 2003 Wiley Periodicals, Inc.