Copper ion binding to N-phenylphthalamic acid studied by 13C nuclear magnetic resonance and electron paramagnetic resonance: model interaction of polyamic acid with copper
Abstract
The interaction of copper with N-phenylphthalamic acid (PPA) cured at various temperatures was investigated by 13C NMR and EPR spectroscopies, as the model system of polyamic acid on copper. EPR spectra prove that copper is dissolved into the PPA–N-methylpyrrolidone solution, producing paramagnetic Cu2+ ions. The 13C NMR resonances of the phthalic group of PPA are selectively broadened due to the paramagnetic interaction between the 13C nuclei and Cu2+ ions, showing binding of Cu2+ to the carboxylate group. Cu2+ ion has no effect on the amide and phenyl groups. Cu2+ ion exchanges rapidly between the carboxylate groups at an exchange rate > 103 s–1 at 23 °C. PPA is imidized to N-phenylphthalimide (PPI) at 150 °C, accompanied by the dissociation of Cu2+. Paramagnetic effects from the Cu2+ ions is not exerted on PPI. The results obtained are compared with the interfacial interaction between polyamic acid and copper.