FT-RAMAN INVESTIGATION OF THE THERMAL CURING OF PMDA ODA POLYAMIC ACIDS

The effect of solvent on the curing reactions of PMDA/ODA polyamic aci ds has been investigated using Fourier transform (FT) -Raman spectrosc opy. Films of different thicknesses were cured by: (1) doctor blading 15% solids solutions onto glass slides, (2) removing all but the bound NMP, and (3) removing all the N-methypyrrolidinone (NMP). The rate of cure and final degree of conversion of the PMDA/ODA polyamic acid to polyimide increased substantially in the presence of NMP, and this eff ect was attributed to the plasticizing effect of the solvent. Below a critical solvent concentration, which was estimated to be approximatel y 40% of the NMP concentration in the bound-solvent limit, the rate of imidization slowed down considerably. Comparison of FT-Raman data for PMDA / ODA polyamic acid: (1) in solution in NMP, (2) complexed with NMP in the solid state, and (3) in the solid state after all the NMP h ad been removed with water, indicated that intermolecular interactions were greatest in the latter case and weakest in solution. Spectra of PMDA / ODA in NMP solution provide strong evidence for binding of NMP to the amide carbonyl in solution.