STUDY ON THE IMIDIZATION OF PARA-ISOMERIC AND META-ISOMERIC UNITS OF AROMATIC POLY(AMIC ACID)S USING SOLID-STATE HIGH-RESOLUTION NMR-SPECTROSCOPY

The content of para- and meta-isomeric units in the products formed at different stages of thermal imidization of the poly(amic acid) prepar ed by condensation of para-phenylene diamine with dianhydride of diphe nyloxidide(3,3',4,4'-tetracarboxylic acid) was estimated using solid-s tate high-resolution C-13 NMR Spectroscopy. Contrary to the procedure used in previous studies, the polymer was not dissolved prior to the s pectra registration; nevertheless, in accordance with the earlier data , it was found that para- and meta-isomeric amic acid units were almos t equally involved in the imidization during the middle stages of the process. It was also found that the solid-state imidization does not c ome to a stop upon cooling of the poly(amic acid) to room temperature, but it continues during the middle and late stages, at a rate of seve ral percent a year.