Abstract
Aromatic poly (amide-imide) (PAI) was prepared by the heating of poly (amic acid-amide) (PAAA) obtained by the polycondensation of trimellitic anhydride chloride with 4, 4'-diaminodiphenylether or 4, 4'-diaminodiphenylmethane in mixed solvent of methyl ethyl ketone with water (MEK/H2O) and in N, N-dimethylacetamide (DMAc). The effects of polymerization solvent and polymer structure on the curing of several PAIs were investigated and the following results were obtained.
(1) The carboxyl group content of PAIs from PAAAs prepared in MEK/H2O was larger than those in DMAc. The carboxyl groups of PAIs were completely blocked by esterification with triethyl orthoacetate.
(2) The curing of PAIs prepared in MEK/H2O proceeded easier than that in DMAc.
(3) The curing of PAIs was retarded by esterification of those carboxyl groups.
(4) PAIs having diphyenylmethane structure was easier cured than those having diphenylether structure in air.
Based on the above results, it was concluded that the curing of PAIs by heating was due to the crosslinking reaction between functional groups of PAI, such as carboxyl and amino groups. Furthermore, the oxidation of diphenylmethane structures of PAIs was considered to play important roles in the curing of PAIs in air.
