END GROUP AND IRREGULAR STRUCTURE-ANALYSIS IN THERMALLY PREPARED SODIUM POLYASPARTATE BY H-1 AND C-13 NMR-SPECTROSCOPY

Sodium polyaspartate (SPA) was synthesized by the hydrolysis of poly(s uccinimide) (PSI) prepared by the thermal polycondensation of L-aspart ic acid at 260 degrees C for 6 h, and the microstructures of the polym er were analyzed in detail using H-1 and C-13 NMR spectroscopy Several end groups and irregular structures which had most likely been produc ed by deamination and decarboxylation were identified and quantified. The presence of branched units was demonstrated by the detailed analys is of the methine proton region using the specially prepared model pol ymers. The number of the branched units was 3 per 100 monomer units, a nd the average number of monomer units between two adjacent branch poi nts and between a branch point and an end group was estimated to be 13 . The comparison of the quantities of the minor structures in SPA with those of the corresponding ones in PSI revealed that side reactions s carcely occur during the hydrolysis of PSI to SPA.