Investigation of Acetyl Ferrocene Migration from Hydroxyl-Terminated Polybutadiene Based Elastomers by Means of Ultraviolet–Visible and Atomic Absorption Spectroscopic Techniques Alper U ¨ nver, 1 Nursel Dilsiz, 2 Mu ¨ rvet Volkan, 1 Gu ¨ neri Akovalı 1 1 Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey 2 Department of Chemical Engineering, Gazi University, 06570 Ankara, Turkey Received 12 January 2004; accepted 18 October 2004 DOI 10.1002/app.21624 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Migration and leakage of some mobile com- ponents in rocket propellant produces an inhomogeneous composition region at which migration takes place, which can lead to premature detonation, changes in ballistic char- acteristics, and so on. It is, therefore, important to be able to predict the behavior of low-molecular-weight mobile addi- tives and to control the leakage of them from the propellant. At this point, our chief interest was to study the magnitude of the migration and to understand the factors that influence the migration process. In this study, the migration of a ferrocene-based burning-rate catalyst [acetyl ferrocene (AcF)] a from hydroxyl-terminated polybutadiene (HTPB) based elastomer in the presence of a plasticizer (dioctyl adipate) was examined in accelerated aging conditions at 60°C for various time intervals. We also tried to minimize the migration of AcF from the loaded to the unloaded part by using an extra barrier layer consisting of polyfunctional aziridine (AST D45+) in addition to the HTPB–toluene di- isocyanate composition. The migration enhanced with aging of the AcF and the barrier effects of the layer with intensified crosslink density to this migration were studied extensively. The migration was monitored by both ultraviolet–visible and atomic absorption spectroscopy (AAS) methods. A com- parison of the data obtained from both of these methods was also done. The two techniques were found to be in agree- ment, and the Fe determinations from both methods were highly correlated, suggesting that the data were reliable, although the AAS data were found to be symmetrically somewhat higher. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1654 –1661, 2005 Key words: HTPB; burn-rate catalyst; aging; migration; UV– vis INTRODUCTION Solid rocket propellants can be regarded as highly filled polymers. The propellant generally consists of about 85 wt % explosive particulate embedded in about 15 wt % elastomeric binder. So, in these highly filled network systems, the migration of some mobile components from more highly concentrated regions to lower ones is not a surprising situation. In migrational motion, individual molecules of the liquid move by “jumping” into adjacent holes formed in the elasto- meric matrix during random thermal motions, which arise from kinetic energy. The thermodynamic drive is due to a tendency to equalize the chemical potential (i.e., concentration) of the diffusing liquid throughout the elastomer. There is no real force pushing mole- cules down the slope of chemical potential, for that is their natural drift as a consequence of the second law and the hunt for maximum entropy. Migration occurs in elastomeric systems as a result of concentration differences in mobile species across bimaterial interfaces (Fig. 1). If the mobile species are not chemically bonded to a substrate material, they will migrate in the direction of lower concentrations. Fick’s law governs simple migration and is given in eq. (1):  c  t  = D   2 c x 2 (1) where c is the concentration, t is the time, x is the distance, and the parameter D is the diffusivity, which is a measure of the mobility of the migrating species. The migration of low-molecular-weight additives, such as plasticizers and burn-rate catalysts, from the propellant into the insulation during curing and aging processes can be extremely hazardous. Many studies have been done to date on the accel- erated aging of laboratory-scale-produced propellant samples. In these studies, it has been reported that the aging rate is strongly dependent on the used storage conditions. 1–3 Moreover, some predictions have been Correspondence to: A. U ¨ nver (aunver@metu.edu.tr). Journal of Applied Polymer Science, Vol. 96, 1654 –1661 (2005) © 2005 Wiley Periodicals, Inc.