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.