Amine-quinone polyimides – High temperature polymers that protect iron against corrosion - Polyimides and Other High Temperature Polymers - page 493

Figure 8. Plot of coating resistance (filled circles) and coating capacitance (open circles) for AQPI-
2 on iron as a function of exposure time to 0.1 M NaCl electrolyte.

creased, indicating that the electrolyte was diffusing into the coating. The AQPI-2
coating (Figure 8) had a higher initial resistance (1.2 x 10 9 ·cm 2 ) and a lower

initial capacitance (2.5 nF/cm 2 ), indicating that AQPI-2 was acting as a good di-
electric. After a year of exposure to the electrolyte, there was little change in the
coating resistance and the coating capacitance for AQPI-2.
A model for the cathodic disbondment of a polymer coating on a metal surface
during blister formation includes the disbondment stress and the elastic modulus
of the coating [16]. A weakness of this model is that the viscoelastic properties of
the polymers are not included. Nevertheless the amine-quinone polyurethanes and
the amine-quinone polyimides provide an opportunity to test this model. We have
already shown that amine-quinone polyurethanes promote adhesion of epoxy to
steel [10]. We speculate that the amine-quinone polymers chemisorb onto the iron
surface, providing a strong adhesion bond. The adhesion bond strength should be
measured and we expect that it would depend on the nature of the amine-quinone
functional group and the number of groups adsorbing onto the iron surface. The
elastic moduli for a series of amine-quinone polyurethanes were in the range of 3
to 250 Mpa [10], while the moduli of the polyimides reported here were 0.9 to 1.5
GPa. The range of moduli provided by the amine-quinone polyurethanes and the
amine-quinone polyimides offer an opportunity to test the effect of elastic
modulus on the rate of blister formation.

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