Chemical Structure of Aromatic Polyamide Degraded by Chlorine

摘要

Aromatic polyamide is one of the high performance polymers, but deteriorates with chlorine. The precise structure of chlorinated aromatic polyamide and the mechanism of the deterioration had not been clarified well. The aromatic polyamide made from 1,3-phenylene diamine (mPDA) and isophthalic acid (IPA) was investigated. The chlorine absorbed in polyamide was said to substitute the amide N-H proton and then rearranged to aromatic ring of mPDA. Chlorine absorption and degradation of polyamide were faster in acidic condition than basic condition. Chlorine contents were about 1.0(pH5) and 0.4(pH9) per repetition unit of polyamide. The chlorinated polyamide structures were investigated with NMR spectra in detail. NMR signals were assigned with 2D-NMR techniques because the conventional additive rule on chemical shifts of chloro-substituted aromatic ring was invalid. 4,6-dichloro-m-PDA derivatives were the main products. The fraction of C-2-substituted component had been assumed to be predominant but found to be very small. Considerable amount of no-chloro-substituted mPDA unit was remained. It was assumed that chlorine substitution had taken place on the surface of film.