Protection of Fe pigments with amine-quinone polymers

High magnetization iron pigments, protected by amine-quinone polymers are described. The amine-quinone polyurethanes were prepared by melt polymerization of 2,5-bis(N-2-hydroxyethyl-N-methylamino)-1,4-benzoquinone, AQM-1, tolylene diisocyanate, and an oligomeric polyether diol; either poly(1,2-butylene glycol) or poly(1,4-butylene glycol). Depending on the choice of polyether and the relative amount of AQM-1, the polyurethanes were elastomeric or thermoplastic; the thermal and mechanical properties being systematically controlled by the polymer structure. Hydrogen reduction of acicular iron oxide pigments gave pyrophoric Fe pigments with an initial σ_s≈195 emu/g. Treatment with a THF solution of the amine-quinone polymer AQPU-8, under an inert atmosphere, gave stabilized Fe pigments with σ_s≈160 to 180 emu/g; a value significantly higher than 140 emu/g for the best ceramic coated pigments. The treated pigments were exposed to the ambient laboratory atmosphere for more than 3000 hours with no loss in σ _s. This demonstration that quinone polymers can replace the ceramic coatings used to protect iron pigments provides a means of significantly enhancing the performance of metal particle tape