Polyimide bonded magnets: Processing and properties

We report a new method of polyimide synthesis based on the interaction of dianhydrides with acylated diamines for preparing a melt processable mixture of prepolymer and rare earth magnetic alloy particles in the form of 75–100 μm particles. This mixture can be easily converted to useful thermoplastic polyimide bonded magnets by heating at 300°C. It is shown that the prepolymer based on 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride and the diacetyl derivative of 2,2-bis(4-(4-aminophenoxy)phenyl)sulfone diamine after removing less than 5% by weight of the volatile components can be melted at 220–240°C to give a fluid with a viscosity of 10–20 Pas. This low viscosity of the prepolymer facilitates blending it with magnetic particles at relatively high volume fractions (up to 85 vol %) that are not possible using conventional methods. The resulting polyimide-bonded magnets exhibit excellent thermal stability and a high storage modulus of 10 GPa at 400°C. Magnetic property measurements showed a ≥10% increase in energy products over that of typical commercial bonded magnet materials such as the ones containing thermoplastic poly(phenylene sulfide) or polyamide matrices. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3151–3158, 2003